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Open Access

Peer-reviewed

Research Article

Exploring risk and protective factors which distinguish suicidal and self-harm behaviours from suicidal and self-harm ideation in young people: A systematic review

  • Marianne E. Etherson ,

    Roles Conceptualization, Data curation, Formal analysis, Investigation, Methodology, Project administration, Writing – original draft, Writing – review & editing

    Marianne.Etherson@glasgow.ac.uk

    Affiliation Suicidal Behaviour Research Lab, School of Health and Wellbeing, University of Glasgow, Glasgow, United Kingdom

    ⨯
  • Sieun Lee,

    Roles Data curation, Investigation, Writing – original draft, Writing – review & editing

    Affiliations Mental Health & Clinical Neurosciences, School of Medicine, University of Nottingham, Nottingham, United Kingdom, Precision Imaging Beacon, University of Nottingham, Nottingham, United Kingdom

    ⨯
  • Krystyna J. Loney,

    Roles Data curation, Investigation, Methodology, Writing – original draft, Writing – review & editing

    Affiliation Suicidal Behaviour Research Lab, School of Health and Wellbeing, University of Glasgow, Glasgow, United Kingdom

    ⨯
  • Isobel P. Steward,

    Roles Writing – original draft, Writing – review & editing

    Affiliation Mental Health & Clinical Neurosciences, School of Medicine, University of Nottingham, Nottingham, United Kingdom

    ⨯
  • Joey Ward,

    Roles Writing – original draft, Writing – review & editing

    Affiliation Suicidal Behaviour Research Lab, School of Health and Wellbeing, University of Glasgow, Glasgow, United Kingdom

    ⨯
  • Heather McClelland,

    Roles Writing – original draft, Writing – review & editing

    Affiliation Suicidal Behaviour Research Lab, School of Health and Wellbeing, University of Glasgow, Glasgow, United Kingdom

    ⨯
  • Aaron Kandola,

    Roles Writing – original draft, Writing – review & editing

    Affiliation MRC Unit of Lifelong Health and Ageing, University College London, London, United Kingdom

    ⨯
  • Josimar A. De Alcantara Mendes,

    Roles Writing – original draft, Writing – review & editing

    Affiliation Responsible Tehcnology Institute, University of Oxford, Oxford, United Kingdom

    ⨯
  • Chris Hollis,

    Roles Conceptualization, Funding acquisition, Writing – original draft, Writing – review & editing

    Affiliations Mental Health & Clinical Neurosciences, School of Medicine, University of Nottingham, Nottingham, United Kingdom, National Institute of Health Research (NIHR) MindTech HealthTech Research Centre, Institute of Mental Health, School of Medicine, University of Nottingham, Nottingham, United Kingdom

    ⨯
  • Ellen Townsend,

    Roles Conceptualization, Funding acquisition, Writing – original draft, Writing – review & editing

    Affiliation School of Psychology, University of Nottingham, Nottingham, United Kingdom

    ⨯
  • Dorothee P. Auer,

    Roles Conceptualization, Writing – original draft, Writing – review & editing

    Affiliations Mental Health & Clinical Neurosciences, School of Medicine, University of Nottingham, Nottingham, United Kingdom, Precision Imaging Beacon, University of Nottingham, Nottingham, United Kingdom

    ⨯
  • Rory C. O’Connor,

    Roles Conceptualization, Investigation, Methodology, Supervision, Writing – original draft, Writing – review & editing

    Affiliation Suicidal Behaviour Research Lab, School of Health and Wellbeing, University of Glasgow, Glasgow, United Kingdom

    ⨯
  • on behalf of the Digital Youth Research Programme

Abstract

Background

Self-harm and suicidal thoughts and behaviours among young people are significant global public health concerns. Although most young people with thoughts of self-harm or suicide do not act on their thoughts, it is important to identify factors that distinguish thoughts of self-harm and suicide from behaviours. To date, there are no reviews distinguishing self-harm and suicidal behaviours from thoughts of self-harm and suicide in young people or that have synthesised factors distinguishing self-harm behaviours from self-harm ideation. The current review addresses these gaps in the literature.

Methods

We systematically searched: CINAHL, Embase, Medline, PsycINFO, Psychology and Behavioural Sciences Collection, and Web of Science Core Collection for articles published between 2011 and April 2024. Ninety-nine studies met inclusion criteria, with 92 articles examining risk and protective factors that distinguished suicide attempts from suicidal ideation and seven articles examining factors that distinguished self-harm behaviours from self-harm ideation. Using a narrative synthesis approach, studies were grouped by their outcome variable (e.g., self-harm or suicide) and then by risk and protective factors.

Results

While findings were inconsistent, the presence of non-suicidal self-injury, physical, emotional, or sexual abuse, violence, and family factors (e.g., family conflict) distinguished suicidal attempts from suicidal ideation. By contrast, the presence of parental factors (e.g., parental connectedness) and greater academic achievement were protective and distinguished suicidal ideation from suicide attempts. Being female, exposure to self-harm/suicide, and impulsivity distinguished self-harm behaviours from self-harm ideation. There was no evidence of protective factors that distinguished self-harm behaviours from self-harm ideation.

Conclusions

The current review highlights important risk and protective factors that distinguish suicidal and self-harm behaviours from suicidal and self-harm ideation in young people. Our review has important implications for intervention and prevention efforts as identifying key risk and protective factors can improve risk assessment for young people experiencing thoughts of self-harm and suicide and enable more targeted interventions.

Citation: Etherson ME, Lee S, Loney KJ, Steward IP, Ward J, McClelland H, et al. (2025) Exploring risk and protective factors which distinguish suicidal and self-harm behaviours from suicidal and self-harm ideation in young people: A systematic review. PLoS One 20(9): e0326381. https://doi.org/10.1371/journal.pone.0326381

Editor: Alemayehu Molla Wollie, Injibara University, ETHIOPIA

Received: September 26, 2024; Accepted: May 29, 2025; Published: September 24, 2025

Copyright: © 2025 Etherson et al. This is an open access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.

Data Availability: All relevant data are within the paper and its Supporting Information files.

Funding: The authors acknowledge the support of the UK Research and Innovation (UKRI) Digital Youth Programme award which is part of the AHRC/ESRC/MRC Adolescence, Mental Health and the Developing Mind programme. Grant number: MR/W002450/1 The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript.

Competing interests: The authors have declared that no competing interests exist.

Introduction

Self-harm and suicidal behaviours in young people are significant public health concerns. Despite challenges in defining self-harm and suicide attempts, self-harm can be broadly defined as self-injurious behaviour irrespective of motive; self-harm is a broad term that can include non-suicidal self-injury (self-injurious behaviour without intent to die) [1,2]. By contrast, self-harm ideation depicts thoughts of self-harm without self-injurious behaviour [2]. Suicide attempts are defined as self-injurious, non-fatal behaviours with at least some evidence of intent to die [1]. Whereas, suicidal ideation is defined as thoughts of ending one’s life, where the risk of suicide can progress from relatively passive thoughts to more active thoughts [1]. Globally, suicide is the third leading cause of death among 15- to 29-year-olds [3]. In addition, a recent meta-analysis examining the global prevalence of self-harm among non-clinical adolescents, found that 22% of adolescents engaged in self-harm behaviours at least once in their lifetime [4]. Evidence also suggests that self-harm and suicidal behaviours are on the rise in young people [5,6]. While many young people experience thoughts of self-harm and suicide, approximately only a third act on their thoughts [7]. It is, therefore, important to better understand the risk and protective factors associated with whether young people with thoughts of self-harm or suicide will engage in self-harm or suicidal behaviours.

Suicide is complex and manifests from an interplay of biological, psychological, social, existential, and cultural factors [8]. Though our understanding of the risk factors for suicide has grown exponentially in recent decades [8], our ability to predict suicide is no better than it was 50 years ago [9]. One possible reason for this it that many common risk factors for suicide did not distinguish between risk factors for suicidal ideation and risk factors involved in the transition from suicidal ideation to suicide attempts [10]. For instance, evidence suggests that many previously identified risk factors for suicide (e.g., depression, hopelessness) are risk factors for suicidal ideation, but not attempts and/or do not significantly distinguish between those with thoughts of suicide and those who attempt suicide [11–13]. The distinction between the development of suicidal ideation and the transition from suicidal ideation to suicide attempts is now widely accepted among researchers and is incorporated into current theoretical models of suicidal behaviour [14,15].

Building on earlier models, Joiner [16] made a critical advance in the literature by proposing that suicidal ideation and attempts have their own distinct risk factors. Since the emergence of Joiner’s Interpersonal Psychological Theory of Suicide [IPTS [16,17];], more contemporary theories of suicide, such as the Integrated Motivational-Volitional Model of suicidal behaviour [IMV [18,19];] and the Three Step Theory [20], have adopted an “ideation-to-action framework” (see Table 1). This framework acknowledges that suicidal thoughts and suicide attempts are separate processes with distinct risk factors [14]. Research has largely supported these theoretical models and the role of acquired capability, volitional factors, and contributors to the capacity for suicide involved in the transition from ideation-to-action [21–23]. Notably, while the “ideation-to-action” framework was developed to better understand suicidal behaviour, it can also extend to self-harm behaviours [ [24]] and is instrumental to better understand those at risk of both self-harm and suicide.

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Table 1. An overview of the main theoretical models based on the ‘ideation-to-action’ framework.

https://doi.org/10.1371/journal.pone.0326381.t001

Two existing reviews have examined the risk factors that distinguish suicide attempts from suicidal ideation through an ideation-to-action framework [10,25]. In the earlier review, May and Klonsky [10] meta-analysed 27 cross-sectional studies comparing risk factors for suicide attempts versus suicidal ideation. Anxiety disorders, post-traumatic stress disorder, drug use disorders and sexual abuse history were the only risk factors to distinguish suicide attempts from suicidal ideation. More recently, Bayliss et al. [25] conducted a systematic scoping review of suicide capability (i.e., a factor by which an individual feels capable of making a suicide attempt). Factors which distinguished suicide attempts from suicidal ideation included painful and provocative events (e.g., abuse, maltreatment), genetic polymorphisms, interoceptive deficits (i.e., decreased ability to perceive bodily sensations), neuroticism, and impaired cognitive functioning.

Although these reviews have been valuable in advancing our understanding of suicide enaction, they are limited to adult populations only, while no reviews have focused on young people [10,25]. Bayliss et al. [25] suggested there may be unique factors involved in the transition from ideation to action in young people (e.g., decision-making capabilities). In addition, because adolescence is a period defined by increased interpersonal sensitivity, impulsivity, and risk-taking behaviours [26], young people are likely to differ from adults in their motivations for attempting suicide. It is possible, therefore, that previously identified risk or protective factors implicated in the transition from ideation to attempts in adults, may not be relevant in young people and there may be unique factors which are specific to younger populations. Consequently, a review identifying the factors involved in this transition in young people is warranted.

Despite research extending the ideation-to-action framework to self-harm [24], to date, no reviews have synthesised the distinct risk or protective factors that distinguish self-harm behaviours from self-harm ideation. Self-harm behaviours are one of the strongest predictors of suicide attempts and are prevalent in young people [27], therefore it is important to synthesize evidence of the factors that may be involved in the transition from self-harm ideation to self-harm behaviour in young people. Thus far, no reviews have synthesised existing work on the distinct risk and protective factors that distinguish young people who have thoughts of self-harm or suicide from those who act on their thoughts. The current review addresses these existing limitations by being the first to synthesise the distinct risk or protective factors which distinguish suicide attempts from suicidal ideation and distinguish self-harm behaviours from self-harm ideation in young people. This comprehensive review provides an important touchstone, synthesising the most up-to-date evidence on the ideation-to-framework in young people, which can be utilised to guide future research, highlight knowledge gaps, and inform future preventative and treatment efforts.

Research question

What risk and protective factors distinguish young people (aged 13–25 years) who have thoughts of self-harm or suicide from those who act on them?

Methods

Search strategy

The current review was registered on PROSPERO (CRD 42022332224) where the search strategy was predefined. The search strategy followed Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) guidelines [28]. The following databases were systematically searched: CINAHL, Embase, Medline, PsycINFO, Psychology and Behavioural Sciences Collection, and Web of Science Core Collection. The original search was conducted on 3rd May 2022 and updated on 11th April 2024. The search was restricted to English language, peer-reviewed articles, and articles published between 2011–2022. The start date of 2011 was chosen based on the publication of the updated IPTS [17] and emergence of the IMV model [18], both ideation-to-action frameworks. Separate searches were conducted independently for each database using the following search terms and Boolean phrases: (i) Thought* OR thinking OR ideat* AND behavi* OR enact* OR attempt*, (ii) self-harm* OR self-injur* OR self-mutilat* OR suicid* OR ideation-to-action, (iii) young people OR youth OR adolescen* OR young adult* OR teen*. The final search combined searches 1–3.

Inclusion and exclusion criteria

For inclusion in the review, studies had to: (a) be a peer-reviewed primary empirical paper of any study type (e.g., quantitative, qualitative, mixed methods); (b) be available in English language (c) include a sample of young people aged between 13–25 years or include a sample with a broader age range than 13–25 years, but where the Mage of participants fell into this range; (d) examine risk or protective factors that distinguished suicide attempts from suicidal ideation or self-harm behaviour from self-harm ideation; and (e) include at least two distinct groups (e.g., a suicidal ideation group with no previous history of suicide attempts vs a suicide attempt group or a self-harm ideation group with no previous history of self-harm behaviour vs a self-harm group) or track the transition from suicidal ideation at baseline (with no prior history of suicide attempts) to suicide attempts or self-harm ideation at baseline (with no prior history of self-harm) to self-harm behaviour over time. While there is no universally established age range for young people, based on various definitions and because suicide attempts are rare below age 13 years [29], and as adolescence is thought to extend until the mid-twenties [30], our classification of young people ranged from 13–25 years.

Conversely, studies were excluded if they: (a) were not a peer-reviewed primary empirical paper (e.g., a review article, case study or commentary); (b) were not available in English language (c) did not include a sample of young people within the age range of 13–25 years or where the majority of participants fall into this range; (d) did not examine risk or protective factors that distinguished suicide attempts from suicidal ideation or self-harm behaviour from self-harm ideation and (e) did not examine two distinct groups (e.g., a suicidal ideation group with no previous history of suicide attempts vs a suicide attempt group or a self-harm ideation group with no previous history of self-harm behaviour vs a self-harm group) or track the transition from ideation to behaviours over time.

Screening

Search results from each database were exported to Endnote. Duplicates were removed electronically in Endnote and manually when articles were exported into an Excel document. The first author assessed the retrieved studies’ titles and abstracts for inclusion. In cases where it was unclear if a study met the inclusion criteria, the study was retained to be screened by its full text. To check for accuracy of the screening process, a second assessor screened a random 10% sample of title and abstracts and a random 20% sample of full-text papers. The two reviewers reached excellent agreement for title and abstract screening (Κappa (K) = 0.81) and substantial agreement for full-text screening (K = 0.65). Any disagreements were resolved through discussion.

Data extraction

Data were extracted by the first author and 10% were cross-checked by a member of the research team. The first author contacted authors of included studies to request any relevant data not reported within manuscripts or supplementary material. The data extracted included author and date of publication, sample type and demographics, study design, country, risk and protective factors examined, outcome measure, significant risk or protective factors found and study results.

Quality assessment

The final studies were assessed for quality. Each study was assigned an overall methodological quality score. The characteristics assessed were guided by a methodological quality assessment instrument, tailored for the current review (see S1 Table for a quality assessment tool and scoring guide). The methodological characteristics evaluated included: (1) methodological design, (2) power calculation of sample size, (3) assessment of suicide and self-harm measures (4) assessment of risk/protective factor measures and (5) confounding variables controlled for. Quality assessments were classified as: 0–2 = very low quality, 3–4 = low quality, 5–6 = reasonable quality, 7–8 = good quality, and = 9–12 excellent/very good quality. Higher scores indicated a lower likelihood of methodological bias and were used to aid interpretation of the study findings. The first author conducted the quality assessment, and a member of the research team assessed 20% of the methodological quality scores for inter-rater reliability. Any disagreements in scores were resolved via discussion with 100% post-discussion concordance. When comparing studies rated low quality (≤ 2; e.g. [31–33],) vs excellent/ very good quality (≥ 9; e.g. [34–36],), there was no evidence of an association between study quality and the nature or significance of the findings.

Data analysis and synthesis

A narrative synthesis was conducted, based on guidelines for reporting a systematic review synthesis, without meta-analysis [37]. Studies were grouped by their outcome variable (e.g., self-harm or suicide) and then by risk and protective factors.

Results

A total of 22,518 articles were retrieved from the initial search and the updated search. Following deduplication, there were 7,070 articles. After applying eligibility criteria at the title and abstract screening stage, 1,176 articles remained. The full text of 1,176 articles were then screened. The main reasons for exclusion included: not being a primary empirical paper (e.g., narrative reviews, systematic reviews, meta-analyses, commentaries), participants not being in the required age range (based on the Mage), examining self-harm/suicidal ideation only or self-harm/suicidal behaviours only, not examining risk or protective factors for self-harm and suicidal ideation and behaviours, and examining ideation and behaviours together as one outcome (e.g., suicidality). Most excluded studies examined risk or protective factors for self-harm ideation and self-harm behaviour or suicidal ideation and suicide attempts, but did not examine risk or protective factors distinguishing between ideation and behaviours. Studies that compared a suicidal ideation group to a control group or a suicide attempt group to a control group, were also excluded. In addition, in line with May and Klonsky’s [10] meta-analytical review, studies examining factors that distinguished between a self-harm ideation group and a self-harm behaviour group or a suicidal ideation group and a suicide attempt group, but did not include a true ideation group (i.e., a proportion of the ideation group had previous history of self-harm or suicidal behaviour, respectively) were excluded.

After screening the full text of 1,176 articles, 96 studies met the inclusion criteria. An additional three articles were identified through handsearching. Therefore, 99 articles were included in this review, with 92 articles examining factors that distinguished suicide attempts from suicidal ideation, and seven articles examining factors that distinguished self-harm behaviour from self-harm ideation (see Fig 1; see Table 2 and 3). All studies that met the inclusion criteria and thus included in the review were quantitative.

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Table 2. Study summary table for suicidal ideation and attempts.

https://doi.org/10.1371/journal.pone.0326381.t002

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Table 3. Study summary table for self-harm ideation and behaviour.

https://doi.org/10.1371/journal.pone.0326381.t003

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Fig 1. PRISMA diagram.

https://doi.org/10.1371/journal.pone.0326381.g001

Narrative synthesis

Study characteristics of studies examining risk and protective factors distinguishing suicide attempts from suicidal ideation

Ninety-two studies examined factors that distinguished suicide attempts from suicidal ideation. The sample size of included studies ranged from 41 to 73,238. Most studies included both female and male samples alongside a small percentage of gender minorities in some studies, whereas two studies were in female only samples [63,124]. The included studies were conducted in the United States (US; N = 52), China (N = 9), Australia (N = 6), United Kingdom (N = 5), Canada (N = 3), Italy (N = 3), Korea (N = 3), Germany (N = 2), Portugal (N = 1), New Zealand (N = 1), Turkey (N = 1), Ethiopia (N = 1), Lebanon (N = 1), Iran (N = 1), Thailand (N = 1) and Brazil (N = 1). One study was conducted across eight countries (Australia, Belgium, Germany, Mexico, Northern Ireland, South Africa, Spain, and the US). All studies were quantitative; seventy-five studies were cross-sectional, 16 were longitudinal and one was experimental [34]. No qualitative studies met the inclusion criteria. Fifty-four studies utilised validated multi-item measures of suicidal ideation and attempts, 36 studies utilised non-validated scales or single item questions. Two studies did not include how suicide ideation/ behaviour was assessed. Most suicide measures were self-report, however one study identified suicidal ideation and attempts through a retrospective analysis of medical records [35].

Methodological quality

Quality assessment criteria and scores for studies examining suicidal ideation and behaviour are reported in the supplementary material (see S2 Table). The maximum score obtainable was 12. The mean score across studies was 5.80 ± 2.03 (range 1–10). The lowest scoring domain was power calculation.

Risk factors distinguishing suicide attempts from suicidal ideation

Sex/ gender

Twenty-nine studies examined gender. Sixteen of these found that suicide attempt groups had a significantly greater number of females, relative to suicidal ideation groups (e.g. [59,66,68],). Whereas, thirteen studies found that gender did not significantly distinguish suicide attempts from suicidal ideation (e.g. [44,69,75],). Conversely, one study found male gender to significantly distinguish suicide attempts from suicidal ideation [144].

Non-suicidal self-injury (NSSI)

Fifteen studies examined NSSI. Of these, 12 identified NSSI to be a risk factor that distinguished suicide attempts from suicidal ideation (e.g. [69,71,113],). Three cross-sectional studies did not find NSSI to significantly distinguish suicide attempt groups from suicidal ideation groups (e.g. [68,83,96],). In addition, two studies reported that a greater number of NSSI methods was also a risk factor (e.g. [12,137],).

Substance use

Thirty studies examined substance use as a risk factor. Eighteen studies found greater substance use (e.g., cocaine use) to significantly distinguish between the suicide attempts and suicidal ideation groups [59,84,136], However, when individual substances were examined in some studies, findings were significant for specific substances only (e.g., marijuana use [59]). Of the eighteen studies, one study examined substance use as one of seven indicators of suicide capability and found that the relationship between suicidal ideation and suicide attempts varied as a function of suicide capability [136]. Conversely, 11 studies found that substance use did not distinguish suicide attempts from suicidal ideation (e.g. [121],). One additional cross-sectional study of American Indian youth found those with a greater proportion of their social network that use alcohol or drugs or that they use alcohol or drugs with significantly distinguished suicide attempts from suicidal ideation [77].

Alcohol use

Twenty studies examined alcohol use. Five studies found greater alcohol use and alcohol-related disorders to significantly distinguish suicide attempts from suicidal ideation [31,35,59,81,142]. The remaining fifteen studies found that alcohol use did not significantly distinguish between suicide attempts and suicidal ideation (e.g. [84,95,127],). One of these studies, however, found that the interaction between major depressive disorder (MDD) severity and frequency of alcohol use significantly distinguished suicide attempts from suicidal ideation [47].

Tobacco use/ smoking

Fourteen cross-sectional studies examined smoking. Eleven studies found greater cigarette smoking to significantly distinguish suicide attempts from suicidal ideation (e.g. [61,83,140],). Whereas, three studies found no significant differences [80,81,84].

Emotional, physical or sexual abuse

Twelve studies examined abuse as a risk factor. Ten studies found at least one form of emotional, physical or sexual abuse (including childhood, recent, or lifetime abuse) to significantly distinguish suicide attempts from suicidal ideation (e.g. [44,92,135],). However, the type of abuse that significantly distinguished between suicide attempts and suicidal ideation were inconsistent across studies. In contrast, two studies found no forms of abuse to significantly distinguish suicide attempt and ideation groups [11,12].

Suicidal ideation frequency, severity and suicidal plans

Fourteen studies examined suicidal ideation, frequency and severity and suicidal plans. Nine cross-sectional studies found greater suicidal ideation severity and duration and suicide plans to significantly distinguish suicide attempts from suicidal ideation (e.g. [40,42,96],). Conversely, four cross-sectional and one longitudinal study did not find greater suicidal ideation/ presence of suicide plans to distinguish suicide attempts from suicidal ideation (e.g. [11,113,132],).

Exposure to suicide or self-harm in friends, family, or significant others

Nine studies examined exposure to suicide or self-harm in others. Four cross-sectional studies and one longitudinal study identified that exposure to suicide or self-harm in others significantly distinguished suicide attempts from suicidal ideation [11,44,95,134,143]. However, three cross-sectional studies [77,105,122] and one longitudinal study [103] found no significant differences.

Violence

Nine cross-sectional studies of adolescents examined violence as a risk factor. Of these, seven found that various forms of violence (e.g., weapon violence victimization; being physically attacked) significantly distinguished suicide attempts from suicidal ideation [47,59,85,97,119,127,133]. However, notably not all forms of violence were significant across studies (e.g., dating violence [97,127,133]). Vélez‐Grau et al. [136] found that no measures of violence significantly distinguished suicide attempts from suicidal ideation. One additional study found that receiving treatment for violent experiences significantly distinguished the suicide attempt group from the suicidal ideation group [31].

Impulsivity

Eleven studies examined impulsivity. Four cross-sectional studies found that higher levels of state or trait impulsivity significantly distinguished suicide attempts from suicidal ideation [66,80,95,143]. However, six studies (five cross-sectional and one longitudinal) did not find impulsivity to distinguish suicide attempts from suicidal ideation [11,31,68,96,98,133]. Valderrama et al. [135] in a cross-sectional study of undergraduates, found that only lack of perseverance distinguished suicide attempts from suicidal ideation, whereas no other impulsivity dimensions distinguished between groups.

Depression

Twelve cross-sectional studies found that depressive disorders/symptoms significantly distinguished suicide attempts from suicidal ideation (e.g. [31,65,119],). Of these, studies suggest the severity of depression is important (e.g. [42],) and identified more severe diagnoses, e.g., MDD/ major depressive episodes as risk factors (e.g. [80],). However, twenty-two studies did not find that depressive disorders/symptoms significantly distinguished suicide attempts from suicidal ideation (e.g. [103,104,121],). One study found that the interaction between frequency of alcohol use and MDD significantly distinguished suicide attempts from suicidal ideation [47]. Conversely, Stewart et al. [132] found less severe depressive symptoms to distinguish suicide attempts from suicidal ideation.

Family functioning

Across nine studies, family factors (e.g., lower parental care and worsening recent relationship quality with parents) significantly distinguished suicide attempts from suicidal ideation (e.g. [83,125,126],). However, one study found that lower parental care predicted suicide attempts in a psychiatric inpatient sample, but not in a high school sample [120]. Four cross-sectional studies found that family factors (e.g., living with a single parent), did not significantly distinguish suicide attempts from suicidal ideation (e.g., family living together, family involvement [69,81,84,125];).

Stressful life events

Four cross-sectional studies examined stressful life events. Two studies of adolescents found that various stressful life events (e.g., serious illness, accident, abuse) significantly distinguished suicide attempts from suicidal ideation [105,106]. Stewart et al. [132] found only interpersonal loss life events to distinguish suicide attempts from suicidal ideation in adolescent inpatients. By contrast, Macrynikola et al. [93] found that stressful life events did not significantly distinguish suicide attempts from suicidal ideation in college students.

Bullying experiences

Nine studies examined bullying experiences. Of these, four studies found that bullying experiences (i.e., being a perpetrator or victim, being kicked, pushed or shoved or made fun of about sex, and being cyberbullied) significantly distinguished suicide attempts from suicidal ideation [59,84,117,137]. However, other types of bullying experiences (e.g., being left out of activities, verbal bullying) examined in these studies did not significantly distinguish suicide attempts from suicidal ideation. By contrast, five cross-sectional studies found no significant differences (e.g. [31,96,97],).

Emotion dysregulation

Four cross-sectional studies [68,80,120,145] examined emotion dysregulation. Of these, two studies found that emotion dysregulation significantly distinguished suicide attempts from suicidal ideation [80,145], whereas two studies found no such difference [68,120].

Physical health

Two cross-sectional studies examined physical health problems and found that cardiovascular disease distinguished suicide attempts from suicidal ideation [60,148].

Brain structure and function

One study examined markers of brain structure [75] and four studies examined markers of brain function [42,104,109,128] using MRI. Of these studies various markers of neural functioning (e.g., amygdala connectivity, amygdala functioning, lower bilateral caudate activity during positive self-processing) and structure (e.g., right lateral orbitofrontal thickness, left fusiform thickness, and left temporal pole volume) significantly distinguished suicide attempts from suicidal ideation, whereas others did not (e.g., caudate activity during negative vs. positive self-appraisals; left caudal anterior cingulate thickness and right rostral anterior cingulate volume).

Biological markers

Five studies examined additional biological markers [38,92–95]. Various biological markers, including greater monocyte count, blunted cortisol reactivity, and lower eosinophil percentages, significantly distinguished suicide attempts from suicidal ideation. However, several other biological markers (e.g., GR-β mRNA, GR sensitivity, and 1L-1β mRNA) did not (e.g. [99],).

Protective factors distinguishing suicide attempts from suicidal ideation

Academic achievement/ Intelligence

Three cross-sectional studies examined academic achievement in adolescent students and found that greater academic achievement significantly distinguished suicidal ideation from suicide attempts [33,133,140]. Likewise, Kwon et al. [31] found low academic performance to significantly distinguish suicide attempts from suicidal ideation. One study examining IQ found no significant differences [122].

Parental factors

One cross-sectional study of adolescent students found that parental factors (e.g., parental connectedness) significantly distinguished suicidal ideation from suicide attempts [105].

Help-seeking

One longitudinal study of adolescents found that for those reporting suicidal ideation, help-seeking behaviours at baseline reduced the onset of suicide attempts over time [62]. However, this finding emerged in Black males and Latinas only.

Anxiety sensitivity

A cross-sectional study of adolescents found that anxiety sensitivity reduced the likelihood of making a suicide attempt among adolescents reporting suicidal ideation [98].

Summary of factors distinguishing suicide attempts from suicidal ideation

Overall, findings were mixed across studies. The most consistent risk factors that distinguished suicide attempts from suicidal ideation included being female, NSSI, physical, emotional, or sexual abuse, violence, and family factors. Although inconsistent, other risk factors identified included age, emotion dysregulation, stressful life events, impulsivity, substance use, bullying, biological markers (e.g., blunted cortisol reactivity), physical health problems (e.g., cardiovascular disease), preferential information processing, affective instability, mental health disorders, psychological distress, suicidal ideation frequency, severity and planning, and unhealthy coping strategies, among others. Protective factors identified included parental connectedness, academic achievement, neighbourhood safety, White ethnicity (in males only) and living with both biological parents (in females only).

Study characteristics of studies examining risk and protective factors distinguishing self-harm behaviours from self-harm ideation

Seven studies distinguished self-harm behaviour from self-harm ideation. Sample sizes ranged from 185 to 30,477. Studies were conducted in the UK (N = 2; Scotland and Northern Ireland), China (N = 1), Southern Ireland (N = 1), and Spain (N = 1). One study was conducted across seven countries (Belgium, England, Hungary, Ireland, Netherlands, Norway and Australia). All studies were quantitative; five studies were cross-sectional, and two were longitudinal [149,157]. No qualitative studies met the inclusion criteria. Three studies employed single-item measures to assess self-harm ideation and behaviour, two did not report a specific measure, and two utilised a validated multi-item measure of self-harm.

Methodological quality

Quality assessment scores for studies examining self-harm ideation and behaviour are reported in the supplementary material (see S3 Table). The maximum score obtainable was 12. The mean score across studies examining self-harm ideation and behaviours was 5.43 ± 2.15 (range 2–9). The lowest scoring domain was power calculation, followed by study design.

Risk factors distinguishing self-harm-behaviours from self-harm ideation

Gender

Two cross-sectional studies of adolescents found that being female significantly distinguished self-harm behaviours from self-harm ideation [24,156].

Exposure to self-harm/ suicide

Three studies in adolescents found that exposure to suicide or self-harm of others distinguished self-harm behaviours from self-harm ideation. Madge et al. [156] examined exposure to suicide/self-harm of others, whereas two other studies examined exposure to self-harm in family or friends [24,149]. O’Connor et al. [24] found that exposure to self-harm in a family member or close friend significantly distinguished self-harm behaviours from self-harm ideation. Whereas, Del Carpio et al. [149] found that only exposure to self-harm in family significantly distinguished self-harm behaviours from self-harm ideation in univariate analyses (no multivariate analyses was conducted). However, this finding did not replicate when examined prospectively.

Impulsivity

Two cross-sectional studies examining trait impulsivity in adolescents found greater impulsivity to significantly distinguish self-harm behaviours from self-harm ideation [24,156]. No studies examined state impulsivity.

Early maladaptive schemas

One study examined early maladaptive schemas and found that the self-harm behaviour group had significantly greater early maladaptive schemas of emotional deprivation, mistrust/abuse, social isolation, defectiveness, failure, dependence and insufficient self-control, compared to the self-harm ideation group [157].

Summary of factors that distinguish self-harm behaviours from self-harm ideation

While research was lacking on risk factors that distinguished self-harm behaviours from self-harm ideation, the most identified risk factors included being female, exposure to self-harm/ suicide, and impulsivity. Additional risk factors included internalization of anger, worse overall functioning, lower self-compassion, lower problem-oriented coping and greater emotion-oriented coping (in females only), worries about sexual orientation and greater life stress. No included studies on self-harm examined protective factors.

Discussion

The aim of this review was to synthesize findings from existing research studies which have examined risk or protective factors in young people that distinguish between those who have thoughts of self-harm or suicide from those who act on their thoughts. Findings were inconsistent across studies. Risk factors that distinguished suicide attempts from suicidal ideation included being female, NSSI, emotional, physical and sexual abuse, violence, and family factors (e.g., conflict). There was also some evidence which found substance/alcohol use, suicidal severity, frequency and planning, emotion dysregulation, and life stress to distinguish suicide attempts from suicidal ideation. Protective factors, including parental factors (e.g., parental connectedness) and academic achievement, distinguished suicidal ideation from suicide attempts. In contrast to the vast number of studies examining factors that distinguish suicide attempts from suicidal ideation, only seven studies examined factors that distinguish self-harm behaviour from self-harm ideation. Here, being female, exposure to self-harm/suicide, and impulsivity significantly distinguished self-harm behaviour from self-harm ideation; however no protective factors were examined.

Notably, the presence of NSSI emerged as the most consistent risk factor that distinguished suicide attempts from suicidal ideation. This finding aligns with a meta-analytical review which found self-harm ideation and behaviours to significantly predict suicide attempts and deaths over time and with research suggesting that self-harm is one of the strongest predictors of future suicide [159,160]. Here, NSSI may represent a clear indication of distress, which if not dealt with, can increase over time. The repeated act of inflicting pain and physical damage on oneself may also desensitise individuals to pain and increase fearlessness of death, particularly because NSSI in young people often escalates in severity over time (e.g. [161],). Consistent with this, while only examined in two studies, Bayliss et al. [25] found interoceptive deficits to distinguish suicide attempts from suicidal ideation. This decreased ability to perceive bodily sensations may increase one’s capacity to engage in NSSI and more lethal self-injury, and subsequently increase the likelihood of transitioning from suicidal thoughts to behaviours (see [16]). Given the prevalence of NSSI in young people (e.g. [4],) and evidence from the current review, NSSI remains an important target for preventative efforts to prevent escalation to suicidal behaviours.

While inconclusive, substance abuse, in addition to physical, emotional, and sexual abuse, were often identified as significant risk factors in distinguishing suicide attempts from suicidal ideation in young people. This finding aligns with May and Klonsky’s meta-analytic review [10] where both drug use disorder and sexual abuse distinguished suicide attempts from suicidal ideation in adults, albeit with modest effect sizes. Likewise, this finding also aligns with Bayliss et al.’s systematic review [25] that found painful and provocative events (e.g., abuse, maltreatment) to significantly distinguish suicide attempts from suicidal ideation in adults. Both substance abuse and physical, emotional, and sexual abuse are associated with increased provocative and painful events which may increase the likelihood of moving from suicidal thoughts to a suicide attempt [17]. Substance abuse may also alter logical thinking and increase the likelihood of engaging in impulsive behaviours. In addition, May and Klonsky [10] suggest that drug use disorders may play a role in the transition due to greater painful physical symptoms (e.g., withdrawal), involvement in risky situations and tolerance to self-inflicted pain (e.g., injecting drugs, overdose), increasing capability of suicide. A departure to May and Klonsky’s review [10], however, is that in the current review, physical and emotional abuse appeared to be a risk factor for suicide attempts in young people, whereas alcohol use did not. These findings indicate possible differences in risk factors between adults and young people.

The severity and frequency of suicidal ideation and the presence of a suicidal plan to distinguish suicide attempts from suicidal ideation emerged as inconsistent across studies in the review (e.g. [11,42],). While suicidal ideation and suicidal plans are well-known predictors of suicide, only suicidal planning has been proposed as a risk factor involved in the transition from suicidal ideation to attempts in some theoretical models [19]. In contrast, all theoretical models of suicide suggest that suicidal ideation progresses to suicide attempts only when one has the capacity to attempt suicide [17,19,20]. Here, it is likely the case that the severity or frequency of suicidal ideation or the presence of a suicide plan alone is not sufficient to transition from thoughts to attempts. It is, therefore, important to consider other contributors, particularly those in regard to capability for suicide, alongside the severity and frequency of suicidal ideation, and suicidal planning.

The ideation-to-action framework is important given that many previously identified risk factors for suicide (e.g., depressive disorders/symptoms) are considered risk factors for suicidal ideation, but not suicide attempts and do not distinguish between these two groups (see [9]). In the current review, findings with depressive disorders/symptoms were mixed. This finding is not surprising based on previous meta-analyses (e.g. [10,162],). Ribeiro et al.’s [162] review, for instance, found that depression conferred risk for suicide ideation, suicide attempts, and suicide death, but found greatest support for depression as a predictor of suicidal ideation. In line with this, May and Klonsky’s meta-analytic review [10] suggests that depression does play a small role in distinguishing suicide attempts from suicidal ideation, but likely plays a bigger role in distinguishing suicidal ideation from control groups given that differences in the prevalence of mental disorders are often much greater between suicidal ideation and control groups, than between suicidal ideation and attempt groups. Depressive disorders/symptoms may, therefore, be somewhat important in facilitating the transition from suicidal ideation to attempts, but alone may not be a key risk factor, and should be considered in combination with other factors.

In this review, findings of state and trait impulsivity were mixed. In studies that found impulsivity to play a role, both state and trait impulsivity distinguished suicide attempts from suicidal ideation (e.g. [95],). While impulsivity is an oft-cited risk factor involved in the transition from suicidal ideation to attempts (e.g. [19],), its role is not consistently supported (see [14]). This inconsistency in findings may be partly explained by the variation in its conceptualization and measurement (see [163]). Impulsivity, for instance, is a multidimensional construct which can refer to both trait and state components and distinct dimensions (e.g., cognitive, behavioural and mood-based impulsivity; see [163]). More attention should be placed on the distinct dimensions of impulsivity given that dimensions vary in their relation to suicidal behaviour (e.g. [164],).

There was, however, no clear pattern to explain why some studies found impulsivity to be important in this transition and other studies did not. Regarding state impulsivity, the timing of measurement seems to be particularly important (i.e., whether impulsivity was measured close to an attempt). For example, Liu et al. [165] found that the length of time between measurement of impulsivity and suicide attempts moderated the relationship between impulsivity and suicide attempts, where the closer the timing of measurement, the stronger the effect. Similarly, using sequence analysis, Townsend et al. [166] have shown that impulsivity is the only factor (from a wide range of risk factors) that is directly proximal to an act of self-harm in young people. Future research is required to disentangle the nature of various dimensions of impulsivity in the transition from suicidal ideation to attempts in young people. Ecological momentary assessment studies may be particularly useful in examining changes in state impulsivity prior to a suicide attempt.

This review offered some indication that exposure to self-harm or suicidal behaviours in family or friends may be a risk factor distinguishing suicide attempts from suicidal ideation, however findings were inconsistent [44,105,143]. Exposure to self-harm and suicidal behaviour has previously been identified as an important risk factor involved in the transition between suicidal ideation and attempts (see [19]). While one study included in this review found that exposure to suicide in friends (but not family) was significantly associated with suicide attempts [143], no consistent patterns emerged across studies in the review. Prior research suggests that exposure to self-harm or suicide in friends may play a more important role in young people who tend to be greatly influenced by their peers and are prone to social contagion. Future research contrasting adolescent and adult samples’ exposure of suicide and self-harm in friends, family, and significant others is warranted. Hawton et al. [167] has noted concerns regarding online exposure to self-harm/ suicide and social contagion in young people. This was evident in Liu et al.’s [86] study included in the review where the suicide attempt group reported significantly greater suicide-related social media use behaviours (i.e., attending to suicide information, commenting on or reposting suicide information or talking about suicide), relative to the suicidal ideation group. Future research should prioritise examining whether online exposure to suicide/ self-harm plays an important role in distinguishing suicide attempts from suicidal ideation in this population.

While interpersonal problems are largely considered to be risk factors for suicidal ideation in theoretical models that incorporate an ideation-to-action framework (e.g., perceived burdensomeness [16];), some interpersonal factors in the current review did distinguish suicide attempts from suicidal ideation. For instance, various interpersonal factors involving family (e.g., family conflict) were found to distinguish suicide attempts from suicide ideation across studies (e.g. [125],). Because adolescence is associated with heightened interpersonal sensitivity, interpersonal problems may increase the likelihood of suicide attempts in this population. Future research comparing adult and adolescent samples on various interpersonal factors within the ideation-to-action framework will be informative. Comparison of other samples (e.g., clinical and non-clinical adolescents) is also warranted given that some interpersonal factors (e.g., lower parental care) only distinguished between suicide attempts and suicidal ideation in a psychiatric sample, but not in a non-clinical sample [120].

In comparison to research examining factors that distinguish suicide attempts from suicide ideation, much less research has focused on factors that distinguish between self-harm behaviours and self-harm ideation. Risk factors for self-harm often overlap with risk factors for suicide (see [2]). This was seen in the current review, where some evidence indicated that being female, exposure to self-harm or suicide, and impulsivity distinguished self-harm behaviours from self-harm ideation and suicide attempts from suicidal ideation. Moreover, the risk factors identified here align with considerable evidence suggesting that self-harm is more prevalent in female adolescents [155], and that factors such as social contagion and impulsivity tend to be more specific to youth (see [26,146]). That said, given the lack of research examining factors that distinguish self-harm behaviours from self-harm ideation, the extent to which these findings would replicate across studies is unclear. Future research examining risk and protective factors that distinguish between self-harm behaviours and self-harm ideation is warranted to provide more conclusive evidence.

Our review found that some protective factors including parental factors (e.g., parental connectedness) and academic achievement distinguished between suicidal ideation and suicide attempts [33,133], whereas we found no evidence for protective factors that distinguished self-harm ideation from self-harm behaviours. Hence, for the most part, findings of the review offer support for a selection of risk factors as important in the transition from suicidal thoughts to suicidal behaviour, rather than protective factors. It is important, however, not to over interpret this finding as relatively few studies focused on protective factors. In this regard, the absence of evidence is not the same as finding that protective factors do not play a role. Future research is needed to determine whether protective factors significantly distinguish between ideation and behaviour groups.

Limitations of the review and future directions

Despite the novel contribution of this review, there are limitations. For example, relevant studies not written in English will have been excluded, limiting generalizations of the findings. In addition, the search was conducted between 2011–2024, therefore relevant studies published before 2011 would not have been retrieved (e.g. [168],). Most studies examining the “ideation-to-action” framework, however, were likely published after 2011 and this review synthesizes more contemporary evidence on this framework. In addition, we excluded studies that did not represent a true ideation group (i.e., where all or some of participants reported previous history of self-harm/ suicidal behaviours; e.g. [38,169–171],). It is possible that ideation groups with previous history of self-harm/ suicidal behaviour differ from true ideation groups on risk factors (e.g., see [170]). Future research should investigate factors that distinguish those who have history of self-harm/suicidal behaviour but experience current ideation only and those who report current ideation and behaviours. Furthermore, there was considerable heterogeneity of variables, including measurement of risk and protective factors and outcome variables and the timescale of measures (e.g., present, lifetime). Therefore, it was not deemed appropriate to conduct a meta-analysis.

Our review was also limited by most eligible studies utilising cross-sectional designs. Future research examining the ideation-to-action framework should employ prospective designs. In addition, only a few studies included in the review recruited samples from low and middle-income countries (e.g. [59,65,107,121,168],). Given that three quarters of the world’s suicides occur in low and middle-income countries and that the greatest burden of self-harm is felt in low-and-middle income countries [172,173], future research examining risk and protective factors that distinguish self-harm behaviours from self-harm ideation or suicide attempts from suicidal ideation in low and middle-income countries is warranted. Our review was also limited by the lack of protective factors examined and by the lack of literature examining risk/protective factors that distinguish self-harm behaviours from self-harm ideation. Future research on the ideation-to-action framework should examine protective factors more broadly and risk/protective factors that distinguish self-harm behaviour from self-harm ideation. Additionally, most included studies relied on self-report measures of psychosocial variables. Future research should examine the role of neural (e.g., adolescent brain maturation) and biological markers in distinguishing between suicidal and self-harm behaviours and suicidal and self-harm ideation. Finally, given the complexity of self-harm and suicidal behaviours, as well as the inconsistencies found in this review, future research should consider examining various combinations of risk and protective factors involved in the transition from thoughts to behaviours.

Conclusion

The ideation-to-action framework has gained momentum in the suicide and self-harm research literature and is recognised as an important framework to identify factors that distinguish between those with thoughts of self-harm and suicide from those who act on their thoughts. This review was the first to synthesise literature examining risk and protective factors that distinguish suicide attempts from suicidal ideation and self-harm behaviours from self-harm ideation in young people. While findings were mixed, the review identified key risk factors distinguishing suicidal attempts from suicidal ideation, predominantly NSSI, physical, emotional and sexual abuse, family factors (e.g., conflict), and violence. Although research was lacking on risk factors distinguishing self-harm behaviours, some risk factors included being female, exposure to self-harm/suicide, and impulsivity. Protective factors distinguishing between suicidal ideation and suicide attempts included parental factors (e.g., parental connectedness) and academic achievement; however, there was no evidence for protective factors distinguishing self-harm ideation from self-harm behaviours. Future work should target and incorporate empirically supported factors into intervention and prevention efforts.

Supporting information

S1 Table. Quality assessment tool and scoring guide.

https://doi.org/10.1371/journal.pone.0326381.s001

(DOCX)

S2 Table. Quality assessment for suicidal ideation and suicide behaviours.

https://doi.org/10.1371/journal.pone.0326381.s002

(DOCX)

S3 Table. Quality Assessment for self-harm ideation and self-harm behaviours.

https://doi.org/10.1371/journal.pone.0326381.s003

(DOCX)

S4 Table. Preferred reporting items for systematic reviews and meta-analyses (PRISMA 2020 Checklist).

https://doi.org/10.1371/journal.pone.0326381.s004

(DOCX)

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