Bidirectional relationship between sexual arousal and (sex-related) disgust

Guangju Wen; Caoyuan Niu; Yikang Zhang; Pekka Santtila

doi:10.1371/journal.pone.0285596

Abstract

Sexual stimuli provoke both sexual arousal and disgust, and the coaction between these emotions determines sexually behavioral outcomes. The current research includes two experiments to explore the bidirectional relationship between sexual arousal toward erotic stimuli and disgust induced by sexual body fluids. Study 1 presented 234 participants (117 women) with sexual body (vs. neutral) fluids followed by erotic stimuli, and Study 2 presented 235 participants (117 women) with erotic (vs. neutral) videos followed by sexual body fluids (and a non-sex-related stimulus). Study 1 showed that exposure to sexual body fluids reduced sexual arousal and the likelihood of sexual engagement toward erotic stimuli in participants with high sexual disgust sensitivity but increased sexual arousal and the likelihood of sexual engagement in participants with low sexual disgust sensitivity, while Study 2 suggested that men exposed to erotic (vs. neutral) stimuli reported lower disgust, stronger sexual arousal state, and higher willingness to interact with the sexual body fluids. There was no relationship between subjective feelings of sexual arousal and disgust in these experiments, while the balance of sexual arousal and disgust toward sexual body fluids and erotic stimuli had a positive association. Also, exposure to erotic stimuli had no effect on reactions to generally disgusting stimulus, but feelings of sexual arousal toward erotic stimuli were positively associated with disgust induced by generally disgusting fluid. These findings suggest that Behavior Immune System regulates disgust to establish a balance between benefit and cost related to sex as well as provide insight into the process underlying sexual dysfunctions.

Citation: Wen G, Niu C, Zhang Y, Santtila P (2023) Bidirectional relationship between sexual arousal and (sex-related) disgust. PLoS ONE 18(5): e0285596. https://doi.org/10.1371/journal.pone.0285596

Editor: José A. Hinojosa, Universidad Complutense Madrid, SPAIN

Received: October 31, 2022; Accepted: April 26, 2023; Published: May 11, 2023

Copyright: © 2023 Wen 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: This research is supported by NYU Shanghai (grant/award number: Startup 10109STARTUPFUND NYU Shanghai; https://shanghai.nyu.edu/) to Pekka Santtila. 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

Sexual dysfunction is a common sexual complaint across different countries and cultures [1–3]. Evidence shows that 25–63% of women and 10–52% of men [4–8] experienced at least one of the sexual dysfunctions and suffered negative outcomes, including depression and anxiety [9]. From an evolutionary perspective, it has been argued that disgust may be involved in sexual dysfunctions given that body fluids such as saliva and semen exchanged during sexual activity involve a contagion risk [10]. Little empirical research has been conducted to explore this hypothesis so far. Thus, the present research explored the associations between disgust induced by sexual body fluids as well as a generally disgusting stimulus and sexual arousal.

Disgust and sexuality

Disgust, one of the basic emotions, is part of the Behavioral Immune System and helps individuals avoid contamination and diseases by eliciting a strong urge to avoid or escape stimuli linked to them [11, 12]. However, sexual activity presents a challenge to the Behavioral Immune System, as it can be considered “disgusting” in at least two ways. First, sexual activity, involving the exchange of body fluids (e.g., saliva, sweat, semen, and vaginal secretions), increases the likelihood of being infected with a sexually transmitted infection [13, 14]. In fact, research shows that fluids, like saliva, are strong disgusting elicitors in non-sexual scenarios [15, 16]. Second, the apertures of the body involved in sexual activities, such as the mouth, vagina, and anus, are also the most sensitive to intrusion and contamination [15].

The information processing model of sexual arousal suggests that the appraisal of sexual stimuli affects the following sexual response [17]. People with negative attitudes toward sexuality experience negative emotions such as fear, shame, and disgust with the occurrence of sexual stimuli, and research has shown that individuals with sexual dysfunctions report higher disgust toward sexual stimuli [18] and pornography use is also related to negative feelings toward erotic stimuli [19]. Brain studies have also found that the presentation of sexual stimuli activates brain networks related to disgust stimuli [20].

Disgust associated with sex is, thus, a powerful emotion that seems to have the function of obstructing sexual activity. This raises the question of how people can engage in sex at all given that it elicits disgust. de Jong et al. (2013) developed a sexual arousal-disgust rival model to elucidate how sexual arousal and disgust induced by sexual stimuli affect the sexual responses of individuals. This model suggests that sexual stimuli elicit both sexual arousal and disgust. The feelings of sexual arousal motivate sexual approach behavior, but the elicited disgust instead facilitates avoidance of sexual stimuli [10]. To make the sexual activity happen successfully, individuals need to down-regulate the feelings of disgust induced by sexual stimuli. On the other hand, a sexually dysfunctional loop would occur in case disgust outweighs sexual arousal [10].

Disgust inhibits sexual arousal

Research has found that disgust inhibits sexual arousal responses and shows a close relationship with sexual problems, especially in women [10]. Supporting this idea that disgust interferes with the development and persistence of sexual arousal [21], research has shown that women with vaginismus (vs. women without vaginismus) report greater overall disgust propensity measured by the Disgust Scale-Revised [22] and stronger disgust responses toward sexual stimuli [23, 24]. Women with female sexual interest/arousal disorder also showed higher heart rate deceleration, suggesting activation of a disgust-related defensive autonomic response, and reported higher feelings of disgust toward erotic stimuli than women without this disorder [18]. Similarly, men with (vs. without) erectile disorder also showed lower willingness to handle sexually contaminated stimuli [24].

Evidence from healthy populations also shows that disgust is associated with decreased sexual arousal. For instance, women reported lower sexual arousal toward the erotic film after being exposed to disgusting pictures [25], while men showed decreases in subjective and genital sexual arousal after smelling a disgusting odor [21]. These inhibiting effects also occurred unconsciously in men and women when a priming paradigm was adopted [26].

Although previous research provides evidence regarding the effects of disgust on sexual arousal, no studies have so far explored whether upregulation of specifically sex-related disgust, that is, disgust induced by sexual body fluids, would affect sexual arousal. Thus, the present study adopted sexual body fluids as sex-related disgusting stimuli, with the idea that these would adequately mimic the actual contamination-related stimuli associated with sexual activity, to explore if sex-related disgust would inhibit feelings of sexual arousal and sexual approach behavior toward subsequent erotic stimuli.

Sexual arousal inhibits feelings of disgust

To engage in sexual activity, humans need to downregulate their feelings of disgust in order to make inherently disgusting sexual activities possible. Previous research has looked at the role of sexual arousal in inhibiting feelings of disgust toward sexual stimuli. Though several experiments have been conducted to explore the effects of sexual arousal on both sex-related disgust and non-sex-related disgust, the results remain somewhat contradictory.

Stevenson et al. (2011) found that male undergraduates reported lower feelings of disgust toward sex-related elicitors but not toward non-sex-related disgust cues after receiving a manipulation that upregulated their level of sexual arousal [27]. Women who received sexual arousal manipulation rated sex-related stimuli as less disgusting (decreases in disgust toward the non-sex-related stimuli were also found) and reported more willingness to finish both sex-related and non-sex-related disgusting tasks [16].

On the other hand, Pawlowska et al. (2020) used an emotion regulation strategy to explore if up-regulating sexual arousal or down-regulating disgust could affect feelings toward erotic videos, but the results showed that up-regulating sexual arousal had no effect on disgust and vice versa [28]. Similarly, evidence from individuals with obsessive-compulsive disorder related to contamination fear found no differences in behavioral or verbal responses to sex-related and non-related disgusting tasks after viewing sexually arousing films [29]. Lee et al. (2014) explored whether the upregulation of sexual arousal affected self-reported measures of trait disgust. Results showed that sexual arousal only reduced sexual disgust but increased pathogen disgust in women and had no effect on male responses [30]. Thus, the second aim of the present research was to explore if sexual arousal would inhibit both sex-related and non-sex-related disgust to explore if the suppressing effects of sexual arousal would be specific to sexual activity.

Understanding how the Behavior Immune System is designed to organize disgust to establish a balance between disgust and sexual arousal helps to understand the occurrence of sexual encounters and problems. The Behavior Immune System triggers disgust to induce avoidance behavior when individuals perceive pathogen cues, but it is also sensitive to the costs and benefits to adjust responses to these disgusting stimuli. For example, disgust temporarily decreases when sexual encounters occur in order for mating and reproduction. However, maladaptive disgust leads to sexual problems. Specifically, excessively high disgust reactions to sexual stimuli reduced individuals’ sexual desire, sexual arousal, and increased sexual avoidance [25, 31, 32]. On the other hand, excessively low disgust caused by sexual arousal might facilitate the development of unusual sexual interest (e.g., urophilia or coprophilia). Previous evidence has shown that men in the sexual arousal group (by imagery or self-stimulation) reported higher willingness to engage in uncommon sexual behaviors (e.g., “sex with extremely fat people”, “getting sexually excited from contact with animals”, “find the 12-year-old girl attractive”) [33]. Individuals’ willingness to engage in such behaviors and not experience feelings of disgust may have been inhibited by sexual arousal [27].

Factors affecting the bidirectional relationship between sexual arousal and disgust

Previous results regarding the bidirectional relationship between sexual arousal and disgust are conflicting [16, 17]. One possibility is that individual differences moderate this bidirectional relationship. According to the sexual arousal and disgust rival model developed by de Jong et al. (2013), sexual stimuli elicit sexual arousal and disgust, while individuals’ trait characteristics may moderate the strength of the feelings elicited by sexual stimuli [10]. Specifically, disgust propensity may moderate the intensity of disgust generated by sexual stimuli, while sexual excitability may moderate the feelings of sexual arousal. Evidence has shown that people with high disgust sensitivity reported higher feelings of disgust toward disgusting stimuli, while those with high sexual inhibition and lower sexual excitability showed less sexual arousal toward erotic stimuli and may have a higher possibility of experiencing sexual difficulties [34, 35].

Gender differences, which show close relations with trait differences, also make contributions to individuals’ feelings toward stimuli and affect the interplay between sexual arousal and disgust. The parental investment theory suggests that women and men have a fundamental difference in obligatory costs related to reproduction [36]. Also, women have a higher risk of being infected by sexually transmitted diseases and of being assaulted sexually, resulting in them being more disgust sensitive and less excitable sexually [12, 37–39]. Similarly, previous research has found that, compared to men, women showed lower sexual excitation, higher sexual inhibition, and higher disgust sensitivity. Thus, these trait differences as well as gender differences may affect the effects of any manipulation of disgust and sexual arousal.

Interestingly, beyond the model from de Jong et al. (2013), research has also shown that disgust sensitivity, especially sexual disgust sensitivity, moderates the strength of sexual arousal elicited by sexual stimuli [40, 41]. This raises a question about whether sexual excitability moderates the disgust response toward disgusting stimuli as well as the effects of disgust on sexual arousal. Thus, the present research explored the effects of disgust sensitivity, sexual excitability, and gender to see if and how these factors affect the interplay between sexual arousal and disgust.

Another key feature of this model is that sexual stimuli induce both sexual arousal and disgust, and the balance between sexual arousal and disgust rather than the sole activation of sexual arousal or disgust determines individuals’ decision-making toward sexual stimuli [10]. Obviously, the use of experimental manipulation (e.g., being exposed to erotic stimuli) would include both of these emotions in the analysis, and the results might be counterintuitive when considering the side emotion elicited by the same stimuli (e.g., disgust elicited by erotic stimuli). Thus, the present research measured the subjective feelings of both sexual arousal and disgust toward each stimulus to explore how sexual arousal and disgust interplay with each other across stimuli.

Given that it is difficult to separate the activation of sexual arousal from disgust toward sex-related disgusting stimuli (and also the activation of disgust from sexual arousal toward erotic stimuli), and given the importance of the effects of the coactions between these two emotions on the behavioral outcomes toward erotic, sex-related, and non-sex-related stimuli, developing a variable that indicates the coaction between sexual arousal and disgust on behavior intention would be an alternative approach. The current study created a new variable named “sexual arousal state” that calculates the balance between sexual arousal and disgust toward the same stimuli to explore how this arousal state affected their reactions toward the subsequent stimuli.

The current study

Previous research has found a bidirectional relationship between sexual arousal and disgust. However, the manipulations of previous experiments used to induce feelings of sex-related disgust (e.g., pictures of naked women with scars or behavioral tasks like lubricating a vibrator) might not adequately represent the actual stimuli present during sexual activity [16, 27]. To improve the ecological validity of the manipulations, sexual body fluids were adopted in the present research. In Study 1, participants first received a sex-related disgust (vs. neutral) manipulation and then rated erotic stimuli to explore if such disgust would adversely impact sexual arousal and sexual approach behavior. Study 2 presented an erotic (vs. neutral) video manipulation first and then sex-related disgust stimuli to explore if sexual arousal can suppress disgust to solve the question of how people can engage in “disgusting” sexual behavior. To explore if the effects of sexual arousal would be specific to sexual body fluids, we also included a non-sex-related disgusting stimulus as a control in Study 2.

The main hypotheses in Study 1 were:

H1.1: Exposing participants to sexual body (vs. neutral) fluid tasks would result in more disgust, higher sexual arousal, and weaker sexual arousal state toward the tasks, as well as lower willingness to finish the tasks. This disgust-inducing effect as well as the inhibiting effect on sexual arousal state and on willingness to finish the tasks would be more pronounced in women, whereas the sexual arousal-enhancing effect would be more pronounced in men.
H1.1b: Women would report more disgust, lower sexual arousal, weaker sexual arousal state, and lower willingness to finish the tasks compared to men.
H1.2: Sexual arousal, sexual arousal state, and the likelihood of sexual engagement elicited by subsequent erotic stimuli would be reduced, whereas disgust elicited by erotic stimuli would be increased after prior exposure to sexual body (vs. neutral) fluid tasks. These effects would be more pronounced in women than men.
H1.2b: Women would report more disgust, lower sexual arousal, weaker sexual arousal state, and lower likelihood of sexual engagement toward the erotic stimuli compared to men.
H1.3: The effects of sexual body fluid tasks on feelings toward subsequent erotic stimuli would be more pronounced in participants with less (vs. more) sexual excitability as well as those with more (vs. less) sexual disgust sensitivity.
H1.4: Feelings of disgust toward sexual body fluids would be negatively related to feelings of sexual arousal and the likelihood of sexual engagement toward erotic stimuli, while sexual arousal toward sexual body fluids would show positive association with these two variables.
H1.5: Sexual arousal state toward sexual body fluids would be positively related to sexual arousal state and the likelihood of sexual engagement toward the erotic stimuli, while sexual arousal state toward the erotic stimuli would mediate the association between the other two variables.

Our main hypotheses in Study 2 were:

H2.1: Exposing participants to erotic (vs. neutral) stimuli would result in higher feelings of sexual arousal, more disgust, and stronger sexual arousal state toward these stimuli. The inducing effects on sexual arousal and sexual arousal state would be more pronounced in men, whereas the disgust-inducing effect would be more pronounced in women.
H2.1b: Men would report higher sexual arousal, stronger sexual arousal state, and less disgust toward the erotic stimuli compared to women.
H2.2: Disgust elicited by subsequent sexual body fluid tasks would be reduced, whereas sexual arousal, sexual arousal state, and willingness to finish the tasks elicited would be increased after prior exposure to erotic (vs. neutral) stimuli. Also, disgust elicited by the generally disgusting fluid task would be reduced, whereas willingness to finish the generally disgusting fluid task would be increased after prior exposure to erotic (vs. neutral) stimuli. The effects of erotic stimuli on feelings toward subsequent sexual body fluid tasks and the generally disgusting task would be more pronounced in men compared to women.
H2.2b: Women would report more disgust, lower sexual arousal, weaker sexual arousal state, lower willingness toward the sexual body fluid tasks, as well as more disgust and lower willingness toward the generally disgusting task compared to men.
H2.3: The effects of erotic stimuli on feelings toward subsequent sexual body fluids tasks and the generally disgusting fluid task would be more pronounced in participants with more (vs. less) sexual excitability and those with less (vs. more) sexual disgust sensitivity.
H2.4: Sexual arousal toward erotic stimuli would be negatively related to disgust but positively related to the willingness to finish both sexual body fluids and generally disgusting fluid tasks, while disgust toward erotic stimuli would be positively related to feelings of disgust but negatively related to the willingness to finish both sexual body fluids and generally disgusting fluid tasks.
H2.5: Sexual arousal state toward erotic stimuli would be positively related to sexual arousal state toward sexual body fluid tasks and the willingness to finish these tasks, while sexual arousal state toward sexual body fluids tasks would mediate the relationship between these two emotions. Also, sexual arousal state toward erotic stimuli would be negatively related to disgust toward generally disgusting fluid task and positively related to the willingness to finish this task, while disgust toward the generally disgusting fluid task would mediate the relationship between sexual arousal state toward erotic stimuli and the willingness to finish the generally disgusting fluid task.

Study 1. The effect of disgust induced by sexual body fluid tasks on reactions to erotic stimuli

Materials and methods

Participants.

The final sample in Study 1 included 234 participants (117 women) with a mean age of 23.19 (SD = 3.67). Demographic information regarding the participants is provided in Table 1.

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Table 1. Demographic variables of the sample.

https://doi.org/10.1371/journal.pone.0285596.t001

Participants were recruited at East China Normal University and through social media (e.g., QQ, WeChat) and received 35CNY for their participation. Participants were included if they met the following criteria: 1) adult; 2) Chinese; 3) heterosexual; 4) not a psychology student or researcher; 5) not pregnant or breastfeeding; 6) no drinking (alcohol), coffee, or other drugs and no masturbation or other sexual activity for at least 12 hours before participating in the experiment.

Fluid type manipulation.

Sexual body fluid and neutral fluid tasks. Eight 30-second videos depicting research assistants completing sex-related behavioral approach tasks were used to induce feelings of disgust related to sexual body fluids (also see Wen et al., 2023) [42]. Four kinds of sexual body fluids including sweat (sweat from the head and neck), saliva, body odor (sweat from an armpit), and genital secretions (semen for female participants and vaginal secretions for male participants) were used. These four ostensibly disgusting body fluids were all fake. Specifically, sweat and body odor was made of a mixture of water and an odorless, watery, and yellowish skin care product. Water sprayed from a plastic spray bottle was used for fake saliva. Semen-like lubricant (white) gel used frequently in adult videos was used to achieve the effect of fake semen, while colorless and transparent lubricant was used for vaginal secretions.

Four of the eight videos presenting a female research assistant completing the male-related body fluids were presented for female participants, while the other four videos presenting a male research assistant completing the female-related body fluids were presented for male participants. All these stimuli were put in a dish with a label indicating the type of fluid. Each video recorded the process where the assistant finished one of the behavioral tasks with three steps: 1) Observe the fluid in the dish, 2) Lift the dish and smell the fluid, and 3) Touch the fluid using their finger (while wearing a plastic glove).

In contrast, eight 30-second videos presenting the research assistant finishing the neutral behavioral approach tasks were used in the control group. The fluids used were sweet water, saline water, soda water, and water.

Introductory videos for fluids. Additionally, to increase the credibility of the fluid videos, we prepared two 30-second introductory videos to introduce information concerning how we obtained each of the fluids. The content of each of the two videos was the same with the only difference being the gender of the research assistant featured in each video. We presented the female version of the videos, recorded by a female research assistant, to the male participants, while we showed the male version of the videos, recorded by a male research assistant, to the female participants.

For the sweat introductory videos, the procedure involved wiping the assistants’ forehead, face, and neck with a cotton ball, which was then deposited into a dish for further use. The introductory videos for body odors, on the other hand, entailed placing a cotton ball under the assistants’ armpit for 15 seconds before removal (with a written notification to participants that the cotton ball had been under the armpit for 5 minutes), followed by depositing the cotton ball into a dish. Semen and vaginal secretions were collected sampling cups. The introductory video for the semen sample featured a research assistant who utilized a pipette to transfer and deposit a sample of “semen” from the sampling cup into a dish. For the introductory video of the vaginal secretions, a research assistant removed the secretions from a sampling cup using a cotton swab.

The introductory videos provided factual information about the preparation of the neutral fluids. Specifically, for water and soda water, the research assistants poured these liquids into a beaker and carefully used a dropper to add small amounts of the fluid into the dish. For saline water and sweet water, the assistants combined salt or sugar with water in a beaker, stirred the mixture with a glass rod, and then deposited a small amount of the solution into the dish using the dropper.

Erotic stimuli. Ten one-minute videos presenting static pictures of nude and semi-nude Asian models (four versions presenting pictures of male models for female participants and four presenting pictures of female models for male participants were created) were created to elicit sexual arousal in individuals. Each video included 15 pictures (7 ~ 8 nude pictures) and each picture was shown for 4 seconds. These pictures were selected from a Chinese erotic picture database randomly and have been shown to induce sexual arousal in the Chinese population [43]. Eight videos (four male versions and four female versions) were used in Experiment 1.

Psychometric instruments.

Socio-demographic data. Socio-demographic data including gender, age, relationship status, sexual orientation, education, occupation, relationship length, monthly income, general physical health, and the total number of sexual partners was collected (see Table 1 for response options).

The Three-Domain Disgust Scale (TDDS). The TDDS [44] including 21 items is designed to measure participants’ disgust sensitivity in three subscales: pathogen disgust (referring to avoidance of infectious microorganisms; e.g., “Seeing a cockroach run across the floor”), sexual disgust (referring to avoidance of sexual partners and behaviors that are detrimental to long-term reproductive success; e.g., “Finding out that someone you don’t like has sexual fantasies about you”), and moral disgust (referring to avoidance of social norm violators; e.g., “Deceiving a friend”). Participants rated the items on a 7- point Likert-type scale ranging from 0 (not at all disgusting) to 6 (extremely disgusting). The internal consistency reliability of the pathogen disgust, sexual disgust, and moral disgust subscales were good in both Study 1 (.67, .76, and .76 respectively) and Study 2 (.66, .81, and .74, respectively).

The Disgust Propensity and Sensitivity Scale-Revised (DPSS-R). The DPSS-R [45] including 16 items measures people’s disgust propensity (the general tendency to respond with the emotion of disgust) via items such as “I avoid disgusting things” and disgust sensitivity (the impact of experiencing the emotion of disgust) via items such as “It scares me when I feel nauseous”, respectively on a 5-point Likert scale ranging from never (1) to always (5). In the current research, the disgust propensity subscale and sensitivity subscale had good internal consistencies in Study 1 (.73 and .76) and Study 2 (.78 and .79).

The Disgust Scale-Revised (DS-R). The 25-item DS-R [22] measures individual differences in disgust sensitivity in terms of core (including food, animals, and body products), animal-reminder (including death and envelope violations), and contamination-based disgust (concerns about interpersonal transmission of essences). Participants circle true or false or rate how much they agree with statements pertaining to their tendencies regarding disgusting stimuli on a 3-point Likert scale (1 = not, 3 = very). The current experiment used total scores, with higher scores referring to higher disgust sensitivity. The Cronbach’s α of the whole scale in Study 1 and Study 2 were .80 and .77, respectively.

The Sexual Desire Inventory (SDI). The 13-item SDI [46] includes two subscales measuring dyadic sexual desire (the expression of desire to behave sexually with another person; e.g., “During the last month, how often have you had sexual thoughts involving a partner?”) and solitary sexual desire (the interest in behaving sexually by oneself; e.g., “How strong is your desire to engage in sexual behavior by yourself?”). Participants were asked to answer questions regarding frequency on an 8-point Likert scale from 0 (not at all) to 7 (more than once a day) and rate other questions on a 9-point Likert scale from 0 (not at all important; much less desire; no desire) to 8 (extremely important; much more desire; strong desire). The Cronbach’s αs of the dyadic sexual desire, solitary sexual desire, and the total scale were good in Study 1 (.91, .87, and .94) and in Study 2 (.91, .86, and .93).

The Sexual Inhibition/Sexual Excitation Scales – Short Form (SIS/SES-SF). SIS/SES-SF [47] consists of 14 items rated on a 4-point scale (1 = strongly agree to 4 = strongly disagree). Six items measure sexual excitation (SES; e.g., “When I think of a very attractive person, I easily become sexually aroused”), four items measure sexual inhibition scale 1 (SIS1; Inhibition because of the threat of sexual performance failure; e.g., “I cannot get aroused unless I focus exclusively on sexual stimulation”), and four items measure sexual inhibition scale 2 (SIS2; Inhibition because of the threat of sexual performance consequences; e.g., “If I realize there is a risk of catching a sexually transmitted disease, I am unlikely to stay sexually aroused”). Cronbach’s αs of SES, SIS1 and SIS2 were .82, .41, and .62 in Study 1, respectively, and .78, .50, and .62 in Study 2.

The Positive and Negative Affect Schedule-Revised (PANAS-R). The PANAS-R [48] includes two 10-item scales measuring positive and negative effects on a 5-point scale of 1 (not at all) to 5 (very much). We selected 9 items randomly (including 4 positive items, 4 negative items, and 1 neutral item) and added two additional items (disgusting and sexually arousing). Only items measuring disgust and sexual arousal after viewing fluid task videos and erotic stimuli were used in the data analyses, while measurement of other items was used to disguise our experiment’s purpose.

Willingness to finish the task. A single item (“Please, imagine that you are the person in the video, to what extent would you be willing to finish this task”) rated on a 9-point scale (1 = not at all, 9 = very) was used to measure participants’ willingness to finish the task.

Likelihood of sexual engagement. A single item (“If an attractive opposite-sex person you met in the videos now wants to have sex with you, to what extent would you accept this invitation”) was rated on a graphic slider ranging from 0 (not at all) to 10 (very likely) was used to indicate their likelihood of sexual engagement.

Sexual arousal state. As mentioned before, we expected that the likelihood of sexual engagement would be affected by the coaction between sexual arousal and disgust. Thus, we developed a new variable named sexual arousal state describing the balance (difference) between sexual arousal and disgust toward the tasks (sexual arousal toward the fluid tasks minus disgust toward the fluid tasks) as well as toward erotic stimuli (sexual arousal toward erotic stimuli minus disgust toward erotic stimuli) measured via PANAS-R. A positive number indicated that sexual arousal was larger than disgust, while higher scores indicated a stronger arousal state.

Procedure.

All the measurements were conducted online via Qualtrics© (www.qualtrics.com). Participants were assigned to the experimental group (videos related to sexual body fluids) or the control group (videos related to neutral fluids) randomly by Qualtrics and then viewed the corresponding videos. For each trial, participants were first asked to finish the PANAS-R measuring their baseline emotions. Then they were informed of the type of fluid in this round and viewed the corresponding introductory video (e.g., “In this round, you will watch a volunteer smell and touch the water; now watch the video below and learn how we got this fluid”) as well as the fluid task video (e.g., “Now please watch how the volunteer completes the task”). PANAS-R and one single item measuring their willingness to finish this task were then answered again. After this, they would view an erotic stimulus aimed at eliciting sexual arousal and again rate the PANAS-R and their likelihood of sexual engagement.

Following this, participants needed to finish all four tasks in their group and then finish an online survey measuring their trait characteristics via Wenjuanxing (www.wjx.cn) the next day. A flowchart of the experiment is presented in Fig 1.

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Fig 1. A flowchart presenting the procedure of Study 1.

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Data analysis.

Mixed linear models using SPSS v25.0 were used to explore whether fluid type affected reactions to fluid videos and erotic stimuli. In these mixed linear models, the participants’ index was used as a Subjects variable and the different task types in each trial were used as Repeated variables. P-values (alpha level < .05) and 95% confidence intervals (not overlapping with zero) were used to indicate statistical significance.

First, a series of 2 (Fluid type: Sexual body fluid tasks vs. Neutral fluid tasks) x 2 (Gender: Women vs. Men) mixed linear models were conducted on reactions to fluid tasks to explore a) whether sexual body fluids tasks successfully induced feelings of disgust and lower willingness (and affected feelings of sexual arousal and sexual arousal state), b) whether these reactions showed significant gender differences, and c) whether the effects of fluid type would be different in men and women.

Second, a series of 2 (Fluid type: Sexual body fluid tasks vs. Neutral fluid tasks) x 2 (Gender: Women vs. Men) mixed linear models on reactions to erotic stimuli were conducted to explore a) whether sexual body fluids tasks would inhibit feelings of sexual arousal and the likelihood of sexual engagement (and feelings of disgust and sexual arousal state) toward erotic stimuli, b) whether these reactions showed significant gender differences, and c) whether the effects of fluid type would be different in men and women.

Third, a series of 2 (Fluid type: Sexual body fluid tasks vs. Neutral fluid tasks) x 2 (Traits: Low vs. High) x 2 (Gender: Women vs. Men) mixed linear models on reactions to erotic stimuli were conducted to explore a) whether the effects of fluid task type on reactions to erotic stimuli would be different in participants with low or high traits and b) whether the moderating effects of traits would be different in men and women. To limit the number of analyses, traits with the best reliability from disgust-related trait characteristics (sexual disgust, moral disgust, and pathogen disgust) and sexual-related trait characteristics (SES, SIS1, SIS2, sexual desire) were used in these analyses. In this case, sexual disgust and SES were included. The means of the traits were used as threshold values for high and low grouping. Participants scoring above the means on traits were allocated to the high group, whereas others were allocated to the low group.

Next, subjective ratings of sexual arousal and disgust of individuals were used to examine if there was a negatively bidirectional relationship between these two emotions. Data from the experimental group was used because no disgust or sexual arousal was expected to be experienced in the control group. Feelings and reactions toward the same question from four different trials were merged into one latent variable and SmartPLS 3.0 was used to do the regression and mediation analyses.

Fourth, we examined if disgust toward sexual body fluids was negatively related to sexual arousal and the likelihood of sexual engagement toward erotic stimuli. We were also interested in if sexual arousal toward sexual body fluids was positively related to sexual arousal and the likelihood of sexual engagement toward erotic stimuli.

Fifth, to explore the coaction between sexual arousal and disgust toward sexual body fluids on reactions to erotic stimuli, we explored if a) sexual arousal state toward sexual body fluids was positively related to sexual arousal state and the likelihood of sexual engagement toward erotic stimuli and b) if sexual arousal state toward erotic stimuli mediated the relationship between sexual arousal state toward sexual body fluids and the likelihood of sexual engagement toward erotic stimuli.

Ethical statement and pre-registration.

The current study involving human participants received approval from the Institutional Review Board of NYU Shanghai (Approval Number is 2021-020-NYUSH-Zhongbei). Written informed consent for participation was waived for this study in accordance with national legislation and institutional requirements. Before completing the experiment, participants were required to read and acknowledge an electronic consent form that displayed all details of the experiments (e.g., eligibility criteria, experiment procedures, the contact information of the Institutional Review Board), and indicate their decision to participate in the experiment by clicking on the "Yes, I agree to participate (and confirm that I am eligible for the study)" button to proceed with the survey. Before the data collection began, a pre-registration was submitted to ASPREDICTED.COM (https://aspredicted.org/WG2_3PD).

Results

Do sexual body fluids induce feelings of disgust and lower willingness?

Table 2 presents the effects of fluid type and gender on reactions to fluid tasks and erotic stimuli from the mixed linear models.

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Table 2. The effect of fluid type and gender on reactions to fluid videos and erotic stimuli.

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H1.1: Exposing participants to sexual body (vs. neutral) fluid tasks would result in more disgust, higher sexual arousal, weaker sexual arousal state toward the tasks, and lower willingness to finish the tasks. This disgust-inducing effect and inhibiting effects on sexual arousal state, willingness to finish the tasks would be more pronounced in women, whereas the sexual arousal-enhancing effect would be more pronounced in men.

There was an effect of fluid type on feelings of disgust, sexual arousal state toward the tasks, and the willingness to finish them (ps < .001). Participants viewing sexual body (vs. neutral) fluid tasks reported more disgust (M_BATBodyfluid = 2.17, SD_BATBodyfluid = 1.21; M_BATNeutral = 1.19, SD_BATNeutral = 0.50), weaker sexual arousal state toward the tasks (M_BATBodyfluid = -0.92, SD_BATBodyfluid = 1.39; M_BATNeutral = -0.04, SD_BATNeutral = 0.60), and a lower willingness to finish them (M_BATBodyfluid = 3.82, SD_BATBodyfluid = 2.41, M_BATNeutral = 7.36, SD_BATNeutral = 2.11). However, there was no effect of fluid type on feelings of sexual arousal toward the tasks (M_BATBodyfluid = 1.25, SD_BATBodyfluid = 0.60; M_BATNeutral = 1.15, SD_BATNeutral = 0.47; p = .159) even though the means were in the expected direction.

There was a significant interaction between gender and fluid type on sexual arousal toward the tasks (p = .006). Men viewing sexual body (vs. neutral) fluid tasks reported higher sexual arousal (M_BATBodyfluid = 1.39, SD_BATBodyfluid = 0.71; M_BATNeutral = 1.21, SD_BATNeutral = 0.57; p = .003), while there was no significant fluid type effect in women (M_BATBodyfluid = 1.08, SD_BATBodyfluid = 0.37; M_BATNeutral = 1.11, SD_BATNeutral = 0.37; p = .344). There were significant interactions between gender and fluid type on feelings of disgust (p = .013), sexual arousal state (p = .001), and willingness to finish the tasks (p = .031). Post hoc analyses showed that both men and women who viewed sexual body (vs. neutral) fluid tasks reported more disgust, weaker sexual arousal state toward the tasks, and a lower willingness to finish the tasks (ps < .001). Instead, men viewing the sexual body fluid (vs. women viewing the sexual body fluid) reported less disgust (M_Men = 2.03, SD_Men = 1.12; M_Women = 2.33, SD_Women = 1.29; p = .001), higher sexual arousal state toward the tasks (M_Men = -.64, SD_Men = 1.38; M_Women = -1.24, SD_Women = 1.33; p < .001) and higher willingness to finish the tasks (M_Men = 4.07, SD_Men = 2.38; M_Women = 3.53, SD_Women = 2.41; p = .013), while there was no significant gender effect on feelings of disgust, sexual arousal state toward the tasks and willingness to finish the tasks (ps > .278) in participants viewing the neutral fluid.

H1.1b: Women would report more disgust, lower sexual arousal, weaker sexual arousal state, and lower willingness to finish the tasks compared to men.

Gender had a main effect on feelings of disgust (p = .018), sexual arousal (p < .001), and sexual arousal state toward the tasks (p < .001). Women reported more disgust (M_Men = 1.63, SD_Men = 0.96; M_Women = 1.70, SD_Women = 1.11), weaker sexual arousal state toward the tasks (M_Men =-0.33, SD_Men = 1.15; M_Women = -0.60, SD_Women = 1.12), and lower sexual arousal toward the tasks (M_Men = 1.30, SD_Men = 0.66; M_Women = 1.10, SD_Women = 0.37). There was no gender difference in the willingness to finish the tasks (p = .157).

Do sexual body fluids affect reactions toward erotic stimuli?

H1.2: Sexual arousal, sexual arousal state, and the likelihood of sexual engagement elicited by subsequent erotic stimuli would be reduced, whereas disgust elicited by erotic stimuli would be increased after prior exposure to sexual body fluid (vs. neutral) tasks. The effects of sexual body fluid tasks on feelings toward subsequent erotic stimuli would be more pronounced in women than men.

As presented in Table 2, fluid type did not affect sexual arousal, disgust, sexual arousal state, or the likelihood of sexual engagement toward erotic stimuli (ps > .351).

There was no significant interaction between gender and fluid type on sexual arousal, disgust, sexual arousal state, and the likelihood of sexual engagement with the erotic stimuli (ps > .320).

H1.2b: Women would report more disgust, lower sexual arousal, weaker sexual arousal state, and lower likelihood of sexual engagement toward the erotic stimuli compared to men.

Gender had main effects on feelings of sexual arousal, disgust, sexual arousal state, and the likelihood of sexual engagement (ps < .001). Men reported higher sexual arousal (M_Men = 2.63, SD_Men = 1.19; M_Women = 1.99, SD_Women = 1.00), less disgust (M_Men = 1.28, SD_Men = 0.58; M_Women = 1.92, SD_Women = 1.07), stronger sexual arousal state (M_Men = 1.35, SD_Men = 1.32; M_Women = 0.06, SD_Women = 1.61), and higher likelihood of sexual engagement with the erotic stimuli (M_Men = 5.66, SD_Men = 3.10; M_Women = 3.26, SD_Women = 2.70).

Do sexuality and disgust-related trait characteristics moderate the effects of disgust induced by sexual body fluids on reactions to erotic stimuli?

Table 3 presents the results of the interactions between fluid type, trait characteristics, and gender on reactions to erotic stimuli.

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Table 3. The interaction between fluid type, trait characteristics, and gender on reactions to erotic stimuli.

https://doi.org/10.1371/journal.pone.0285596.t003

H1.3 The effects of sexual body fluid tasks on feelings toward subsequent erotic stimuli would be more pronounced in participants with less (vs. more) sexual excitability as well as those with more (vs. less) sexual disgust sensitivity.

Regarding the moderating effect of sexual excitability, there was no interaction between fluid type and sexual excitability (ps > .103) or interaction between fluid type, sexual excitability, and gender (ps > .463) on sexual arousal, disgust, sexual arousal state, or the likelihood of sexual engagement with the erotic stimuli.

Regarding the moderating effect of sexual disgust sensitivity, there was a significant interaction between fluid type and sexual disgust sensitivity on sexual arousal (p < .001; See Fig 2A) and the likelihood of sexual engagement (p = .009; See Fig 2B). Participants with low sexual disgust sensitivity viewing sexual body fluid (vs. neutral) tasks reported higher sexual arousal (M_BATBodyfluid =2.85, SD_BATBodyfluid =1.32; M_BATNeutral = 2.29, SD_BATNeutral = 0.97; p < .001) and higher likelihood of sexual engagement (M_BATBodyfluid = 5.83, SD_BATBodyfluid = 3.15; M_BATNeutral = 5.02, SD_BATNeutral = 3.16; p =.094), while participants with high sexual disgust sensitivity viewing sexual body fluid (vs. neutral) tasks reported lower sexual arousal (M_BATBodyfluid = 1.96, SD_BATBodyfluid =1.05; M_BATNeutral = 2.16, SD_BATNeutral = 1.14; p = .081) and lower likelihood of sexual engagement (M_BATBodyfluid = 3.33, SD_BATBodyfluid = 2.89; M_BATNeutral = 3.69, SD_BATNeutral = 2.77; p = .043). There was no interaction between fluid type and sexual disgust sensitivity on disgust or sexual arousal state toward erotic stimuli (ps > .052).

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Fig 2. The interaction between fluid type and sexual disgust sensitivity on reactions to erotic stimuli.

Note: + p < .10, * p < .05, *** p < .001.

https://doi.org/10.1371/journal.pone.0285596.g002

There was also a significant interaction between task type, sexual disgust sensitivity, and gender (p = .017) on the likelihood of sexual engagement. Men with low sexual disgust sensitivity viewing sexual body fluid (vs. neutral) tasks reported higher likelihood of sexual engagement (M_BATBodyfluid = 6.46, SD_BATBodyfluid = 3.05; M_BATNeutral = 5.63, SD_BATNeutral = 3.08; p = .018), while men with high sexual disgust sensitivity viewing sexual body fluid (vs. neutral) tasks reported lower likelihood of sexual engagement (M_BATBodyfluid = 3.66, SD _BATBodyfluid = 3.38; M_BATNeutral = 5.20, SD_BATNeutral = 2.52; p = .007). There was no fluid type difference in women with low (p = .599) or high (p = .554) sexual disgust sensitivity.

Are the subjective feelings of disgust and sexual arousal induced by sexual body fluid tasks associated with sexual arousal and the likelihood of sexual engagement toward erotic stimuli?

Fig 3 presents the associations between subjective feelings toward sexual body fluids and reactions to erotic stimuli.

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Fig 3. The associations between subjective feelings toward sexual body fluids and reactions to erotic stimuli.

Note: Number outside the brackets = β; Number in the brackets = p-value.

https://doi.org/10.1371/journal.pone.0285596.g003

H 1.4.1 Feelings of disgust toward sexual body fluids would be negatively related to sexual arousal and the likelihood of sexual engagement toward erotic stimuli.

As presented in Fig 3A, feelings of disgust toward sexual body fluids had no relationship with sexual arousal and the likelihood of sexual engagement toward erotic stimuli (ps > .118).

H 1.4.2 Feelings of sexual arousal toward sexual body fluids would be positively related to sexual arousal and the likelihood of sexual engagement toward erotic stimuli.

Results showed that feelings of sexual arousal toward sexual body fluids were positively related to sexual arousal and the likelihood of sexual engagement toward erotic stimuli (ps < .001)

Does sexual arousal state toward sexual body fluids affect sexual arousal state and the likelihood of sexual engagement toward erotic stimuli?

H 1.5.1 The sexual arousal state toward sexual body fluids would be positively related to sexual arousal state and the likelihood of sexual engagement toward erotic stimuli.

Regression analyses showed that sexual arousal state toward sexual body fluids was positively related to sexual arousal state toward erotic stimuli (β = 0.41, p < .001) but not related to the likelihood of sexual engagement (β = 0.18, p = .146)

H 1.5.2 Sexual arousal state toward sexual body fluids would affect the likelihood of sexual engagement toward erotic stimuli via its effect on sexual arousal state toward erotic stimuli.

As presented in Fig 3B, sexual arousal state toward sexual body fluids was positively related to sexual arousal state toward erotic stimuli (p = .007), and sexual arousal state toward erotic stimuli was positively related to the likelihood of sexual engagement toward erotic stimuli (p < .001). Sexual arousal state toward erotic stimuli mediated the relationship between sexual arousal state toward sexual body fluids and the likelihood of sexual engagement and the standardized indirect effect was 0.23 (95% CI [.18, 1.45]).