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Effects of Facial Skin Smoothness and Blemishes on Trait Impressions

People make trait inferences based on facial appearance, and these inferences guide social approach and avoidance. Here, we investigate the effects of textural features on trait impressions from faces. In contrast to previous work, which exclusively manipulated skin smoothness, we manipulated smoothness and the presence of skin blemishes independently (Study 1) and orthogonally (Study 2). We hypothesized that people are particularly sensitive to skin blemishes because blemishes potentially indicate poor health and the presence of an infectious disease. We therefore predicted that the negative effect of blemished skin is stronger than the positive effect of smoothed skin. The results of both studies are in line with this reasoning. Across ratings of trustworthiness, competence, maturity, attractiveness, and health, the negative influence of skin blemishes was stronger and more consistent than the positive influence of skin smoothness (Study 1). Moreover, the presence of skin blemishes diminished the positive effect of skin smoothness on attractiveness ratings (Study 2). In sum, both facial skin blemishes and facial skin smoothness influence trait impression, but the negative effect of blemished skin is larger and more salient than the positive effect of smooth skin.

represents an evaluation of a target's attractiveness (Sutherland et al., 2013). Together, these three dimensions reflect the functional nature of face judgments. Judging a person's intention and ability constitutes an appraisal of their threat potential and determines who is approached or avoided (Oosterhof & Todorov, 2008). Likewise, judging attractiveness constitutes an appraisal of a person's mate value and determines who is sought out as a sexual partner (Rhodes, Simmons, & Peters, 2005). Spontaneous face judgments thus provide perceptual input that guides social behavior. In line with this reasoning, judgments of trustworthiness, competence, and attractiveness influence behavior in a wide variety of domains such as criminal sentencing (Gunnell & Ceci, 2010;Wilson & Rule, 2015), voting (Berggren, Jordahl, & Poutvaara, 2010;Todorov, Mandisodza, Goren, & Hall, 2005), personnel selection (Bo´o, Rossi, & Urzu´a, 2013;Gomulya, Wong, Ormiston, & Boeker, 2016), and social exchange (van't Wout & Sanfey, 2008).
Given the pervasive influence of face judgments on social behavior, it is important to understand which facial cues drive trait perceptions. So far, research has largely focused on the structural (e.g., facial width-to-height ratio, Stirrat & Perrett, 2010) and dynamic (e.g., emotional expressions, Sutherland, Young, & Rhodes, 2016) properties of faces. Relatively, little is known about the role of textural properties or the specific textural properties that influence trait impressions. This is surprising, given that a person's facial skin texture can be a valid indicator of their health and personality (Jones, Kramer, & Ward, 2012).
Existing studies have examined the influence of skin smoothness on perceptions of health and attractiveness. For example, health ratings of skin patches cropped from a face are correlated with attractiveness ratings of the entire face, suggesting that skin surface features contribute to perceptions of attractiveness (Jones, Little, Burt, & Perrett, 2004). Fink, Grammer, and Thornhill (2001) also showed that a statistical measure of skin homogeneity (indexed by the correlation between neighboring pixels in a facial photograph) is positively related to perceived attractiveness. Recently, Tsankova and Kappas (2016) examined the effects of skin smoothness on a wider set of trait impressions. They found that targets whose skin had been smoothed with computer software were seen as more trustworthy, competent, attractive, and healthy which led them to conclude that having smooth skin has a positive influence on trait impressions. 1 Here, we seek to extend their findings by proposing that facial blemishes, more so than smooth skin, play an important role in impression formation.
With their manipulation of facial smoothness, Tsankova and Kappas (2016) eliminated common variations in skin texture such as wrinkles, uneven pigmentation, large pores, or birth marks. However, this manipulation also resulted in the removal of facial skin blemishes, which were present on some individuals. It is thus unclear to what extent the influence of facial skin texture on trait impressions is driven by the presence of facial blemishes as opposed to smooth skin per se. Prior work has shown that people are particularly sensitive to cues connoting poor health in order to prevent contact with sick individuals (Schaller & Duncan, 2007). Thus, people may be particularly sensitive to the presence of blemishes. This view predicts more negative trait impressions of individuals with facial blemishes.
Moreover, the effect of blemishes may be stronger and more salient than the effect of smoothness. To investigate this question, we disentangle the unique roles of skin smoothness and skin blemishes in impression formation. Avoiding sick individuals is crucial for survival (Park, Schaller, & Crandall, 2007) and people rely on facial cues to infer a person's health (Henderson, Holzleitner, Talamas, & Perrett, 2016;Matts, Fink, Grammer, & Burquest, 2007). In fact, prior work suggests that people can identify individuals with an experimentally induced sickness just on the basis of a facial photograph (Axelsson et al., 2018;Regenbogen et al., 2017). Since the cost of a false positive (engaging with a sick individual) substantially outweighs the cost of a false negative (avoiding a healthy individual), even cues that resemble the symptoms of an infectious disease can trigger avoidance (Nesse, 2005; see also Zebrowitz & Rhodes, 2004). For example, individuals with benign facial irregularities (e.g., a port wine stain) are treated as a potential source of contagion (Houston & Bull, 1994;Ryan, Oaten, Stevenson, & Case, 2012). Similarly, we posit that this heightened sensitivity to disease cues might lead people to attribute common facial skin blemishes to the presence of a harmful disease, rather than a more probable noninfectious condition (e.g., acne). Ultimately, this vigilance could lead to more negative impressions of individuals with facial skin blemishes.
Here, we provide a more nuanced test of the influence of facial skin texture on trait judgments by manipulating skin smoothness and blemishes independently (Study 1) and orthogonally (Study 2). Both studies were preregistered, and all data and analysis scripts are available at the Open Science Framework (https://osf.io/6drqn/) We report how our sample sizes were determined and all data exclusions, manipulations, and measures in the studies.

Study 1
In our first study, we replicated earlier work by Tsankova and Kappas (2016) by comparing people's judgments of individuals with smooth facial skin against an unmanipulated baseline version. Crucially, we also compared judgments of individuals with facial skin blemishes to an unmanipulated baseline version. We hypothesized that the effect of facial skin texture on people's trait judgments is primarily due to more negative evaluations of blemished faces, rather than more positive evaluations of smooth faces. In addition to judgments of trustworthiness, competence, and attractiveness, we also assessed health judgments (in a pretest) and maturity judgments of the faces. Tsankova and Kappas (2016) raised the possibility that more positive trustworthiness judgments of individuals with smoothed skin are driven by more positive judgments of other traits, such as maturity, which are related to trustworthiness. This argument contrasts previous findings showing that individuals with smooth skin are perceived to be younger (Tiddeman, Burt, & Perrett, 2001). Therefore, we tested whether smooth skin has a positive or negative effect on perceived maturity. Prior work has also shown that averaging (i.e., morphing) faces leads to a healthier and more attractive appearance, and one proposed explanation for this effect is that averaging creates a smooth skin texture free of blemishes (Fink et al., 2001;Little & Hancock, 2002). We tested this explanation directly by comparing the independent effects of blemishes and smoothness on health and attractiveness judgments.

Methods
Participants. Our sample size was based on the number of students who participated in the study within two weeks, with a minimum set at 150. This provided us with at least 25 independent judgments for each face (cf. Oosterhof & Todorov, 2008). We recruited 233 Tilburg University students on campus. The study was administered on a tablet, and participants who completed the study were entered in a raffle for one of three vouchers for a local cafe´. It was ensured that participants completed the study in a quiet environment without any distractions. In line with our preregistered exclusion criteria, we excluded six participants (2.58%) who always gave the same rating, 10 participants (4.29%) who indicated that they had noticed our manipulation of facial skin texture, and 14 participants (6.01%) who indicated that they had seen the unmanipulated faces in a previous experiment. This resulted in a final sample of 203 participants (58.1% females; M age ¼ 22.16, SD age ¼ 4.66).
Materials. Similar to Tsankova and Kappas (2016), we used photos from the Radboud Faces Database (Langner et al., 2010). We selected 10 male and 10 female individuals with a frontal gaze and a neutral facial expression. In contrast to Tsankova and Kappas (2016), no individuals with skin blemishes were included. Targets' average estimated age ranged from 20 to 30 years (M age ¼ 23.81, SD age ¼ 3.67), and we ensured that there were no gender differences in age, t(13.25) ¼ 0.92, p ¼ .38. 2 Drawing on Langner et al. (2010) validation study of the face database, we also ensured that there were no gender differences in perceived attractiveness of the individuals, t(15.46) ¼ 0.42, p ¼ .68.
The images were cropped to an oval shape measuring 500 Â 600 pixels, and three different versions of each face were created (for a total of 60 stimuli): an unmanipulated baseline version, a smoothed version, and a blemished version (see Figure 1). The images were manipulated using the GNU Image Manipulation Program (GIMP) 2.8.22 (Free Software Foundation Inc, 2017). For the smoothed version, we first created a duplicate layer of the face image and applied a Gaussian blur filter (level 10) to the bottom layer. We then removed the target areas of the top layer so that the smoothed bottom layer became visible. This ensured that only the relevant skin areas of the face would appear smoothed. For the blemished version, we first downloaded images of individuals with acne from the Internet. We cropped the blemished areas from the faces to create different patches of blemished skin. These patches were then added to our target faces to mimic the presence of mild acne. Different numbers and combinations of acne patches were applied, and their rotation, transparence, and contrast were varied to ensure that the manipulated faces looked realistic. As can be seen from the sample stimuli shown in Figure 1, the manipulations were subtle and meant to reflect common variations in skin texture.
Pretest of face stimuli. We conducted a pretest to check whether our manipulation of the faces was strong enough to influence participants' health judgments, but not too strong, so that they would be suspicious of our manipulation. We recruited 61 MTurk workers (45.9% females; M age ¼ 35.20, SD age ¼ 12.77) to rate the perceived health of the faces in exchange for 50 cents. Participants were randomly allocated to one of three different stimulus sets. After providing written informed consent, they rated the health of 20 faces (six or seven blemished, baseline, and smoothed faces) on a scale from 1 (not healthy at all) to 9 (extremely healthy). Specifically, participants were shown one face at a time and asked how healthy they think the person in the photo is. Importantly, they only saw one version of each individual. In other words, each of the 20 faces was rated by all participants but which of the three versions of the face was shown varied between sets. We calculated the intraclass correlation coefficient (ICC) as a measure of interrater consistency. Participants showed significant consensus in their health ratings (ICC mean ¼ .259, all ps < .001).
We estimated a linear mixed-effects regression model with random intercepts per participant and face to test for the effects of skin smoothness and blemishes on health ratings. We found a negative effect of blemished skin on health ratings, b ¼ À0.842, SE ¼ 0.086, t(1,138.5) ¼ 9.75, p < .001, 95% confidence interval (CI) ¼ [À1.017, À0.663], and a positive effect of smoothed skin, b ¼ 0.530, SE ¼ 0.086, t(1,139.5) ¼ 6.13, p < .001, 95% CI [0.342, 0.698]. We also found a significant difference in the magnitude of the two effects, z ¼ 2.55, p ¼ .011, showing that the effect of blemished skin on health ratings was significantly stronger than the effect of smoothed skin. Thus, our manipulation of the faces was successful. For the main study, we selected 18 faces (nine males and nine females) in order to have an equal number of faces within each skin condition (six blemished faces, six baseline faces, and six smoothed faces). We omitted two faces (one male and one female) that showed little to no differences in perceived health across the three skin conditions. Procedure and design. Three stimulus sets were created. Each set contained all 18 faces, but which version of the face was included differed between sets. Each set contained six baseline, six smoothed, and six blemished faces, and every participant only rated one set. Participants were randomly allocated to one of two conditions that determined which traits they were going to rate. In one condition, they first rated the faces on trustworthiness and then on maturity, and in the other condition, they first rated the faces on competence and then on attractiveness. Thus, all participants were assigned to a 2 (Trait condition: trustworthiness/ maturity vs. competence/attractiveness) Â 3 (Facial skin: blemished vs. baseline vs. smoothed) design, with trait condition as a between-subject factor and facial skin as a within-subject factor.
After providing written informed consent, participants were shown one face at a time in a random order and were asked to rate the face on the relevant trait on a scale from 1 (not [trait] at all) to 9 (extremely [trait]). Participants showed significant consensus in their trait ratings

Results
To test whether the facial skin manipulation affected trait ratings, we estimated separate linear mixed-effects regression models for each trait. We used dummy variables to compare the blemished and smooth versions with the baseline version of each face. In all models, we included participants and faces as random effects to account for variation in ratings across participants (i.e., differences in average ratings between participants) and across stimuli (i.e., differences in average ratings between faces). 3 We predicted that the blemished faces would be rated as less trustworthy, competent, mature, and attractive compared to the baseline faces. We predicted no difference in ratings for the smoothed faces compared to the baseline faces. We also conducted z tests to compare the magnitude of the effect of blemished skin to the magnitude of the effect of smoothed skin. We used the lme4 package (Bates, Ma¨chler, Bolker, & Walker, 2015) in R (R Core Team, 2017) to estimate mixed-effects regression models and the lmerTest package (Kuznetsova, Brockhoff, & Christensen, 2016) to obtain p values.
Trustworthiness. First, we regressed participants' trustworthiness ratings of the faces on facial skin condition. There was a negative effect of blemished skin on trustworthiness ratings, b ¼ À0.191, SE ¼ 0.071, t(1,700.1) ¼ 2.69, p ¼ .007, 95% CI [À0.339, À0.050], and a positive, but only marginally significant effect of smoothed skin, b ¼ 0.122, SE ¼ 0.071, t(1,700.1) ¼ 1.71, p ¼ .087, 95% CI [À0.018, 0.262]. In line with our hypotheses, we found that, when compared to the baseline faces, the blemished faces were perceived as less trustworthy, but we found no clear evidence that the smoothed faces were perceived as Figure 2. The graph shows the difference in ratings of the blemished (BL) faces (black diamonds) and of the smoothed (SM) faces (white dots) when compared to ratings of the baseline faces for each trait. Positive deviations from zero (i.e., the rating of the baseline faces) denote more positive ratings, whereas negative deviations denote more negative ratings. Error bars reflect 95% confidence intervals, and p values were derived from a z test comparing the magnitude of the two effects. more trustworthy (see Figure 2). A z test comparing the strength of both effects revealed no significant difference, z ¼ 0.69, p ¼ .49.
Competence. Next, we regressed participants' competence ratings of the faces on facial skin condition. There was a negative effect of blemished skin on competence ratings, b ¼ À0.370, As predicted, we found that, when compared to the baseline faces, the blemished faces were perceived as less competent, but the smoothed faces were not perceived as more competent (see Figure 2). We also found a significant difference between the effect of blemished skin and the effect of smoothed skin, z ¼ 2.92, p ¼ .004, showing that the effect of blemished skin on competence ratings was significantly stronger than the effect of smoothed skin.
Attractiveness. Finally, we regressed participants' attractiveness ratings of the faces on facial skin condition. Results showed a negative effect of blemished skin on attractiveness ratings, b ¼ À0.758, SE ¼ 0.070, t(1,715.1) ¼ 10.86, p < .001, 95% CI [À0.895, À0.621], and a positive effect of smoothed skin, b ¼ 0.295, SE ¼ 0.070, t(1,715.1) ¼ 4.23, p < .001, 95% CI [0.159, 0.432]. As predicted, we found that the blemished faces were perceived as less attractive when compared to the baseline faces (see Figure 2). The smoothed faces, on the other hand, were perceived as more attractive when compared to the baseline faces. We found a significant difference between the effect of blemished skin and the effect of smoothed skin, z ¼ 4.68, p < .001, showing that the effect of blemished skin on attractiveness ratings was significantly stronger than the effect of smoothed skin.
The influence of target gender. We also examined the influence of target gender (the gender of the person displayed in the image) on trait ratings by regressing participants' ratings on facial skin, target gender (coded À1 for male and 1 for female), and the interaction between facial skin and target gender separately for each trait.
For trustworthiness ratings, we still found a negative effect of blemished skin, b ¼ À0.192, Accounting for random variation in the effect of blemishes. When creating the blemished versions of the faces, we used different combinations of blemishes for each face in order to create realistic stimuli. Since the amount and severity of blemishes consequently differed between faces, we would expect variation in the magnitude of the effect of blemishes on participants' trait ratings between faces. We therefore ran additional mixed-effects regression models that included random slopes for the effect of facial skin for each target to test the robustness of our results. Comparing models with and without random slopes showed that including random slopes significantly increased model fit for ratings of attractiveness, (5) ¼ 28.85, p < .001. However, the effects of blemished skin and smoothed skin on attractiveness ratings remained virtually unchanged. Including random slopes did not increase model fit for ratings of trustworthiness, (5) ¼ 0.17, p ¼ .99, competence, (5) ¼ 2.65, p ¼ .75, or maturity, (5) ¼ 3.17, p ¼ .67.

Discussion
In Study 1, we investigated the independent effects of facial skin smoothness and facial skin blemishes on trait judgments. Results showed that faces with skin blemishes were seen as less trustworthy, competent, mature, attractive, and healthy compared to the unmanipulated version of the faces. Results for the smoothed faces were less clear-cut. The positive effect of smoothed skin on trait ratings was only marginally significant for trustworthiness ratings and not significant for competence ratings. Smoothed skin was related to higher perceived attractiveness and health. However, the positive effect of smoothed skin on attractiveness held only for female but not for male targets. More importantly, and in line with our hypothesis that blemishes are a more salient cue than smoothness, we found that the negative effect of blemishes on trait ratings was stronger than the positive effect of smoothness for impressions of attractiveness, health, and competence (but not trustworthiness).
Finally, Tsankova and Kappas (2016) raised the possibility that any positive effect of skin smoothness on trait impressions might be due to higher perceived maturity. This argument stands in contrasts with other work showing that smooth skin is associated with youthfulness (Sutherland et al., 2013;Tiddeman et al., 2001). In support with the latter reasoning, we found that smoothed faces were seen as less mature than the unmanipulated baseline faces. In sum, our results suggest that people form more negative trait impressions of individuals with facial skin blemishes. Moreover, the negative influence of blemishes on impressions was stronger and more consistent across different traits than the positive influence of skin smoothness.

Study 2
We have argued that due to a heightened sensitivity for cues indicating poor health, people's trait impressions are more strongly affected by the presence of skin blemishes than by smooth skin. A specific prediction that follows from this hypothesis is that impressions should be influenced more strongly by blemishes than by smooth skin. The results of Study 1 clearly supported this prediction. Another plausible prediction is that the positive effect of smoothness should vary as a function of whether or not blemishes are present. If blemished skin is a more salient cue in the process of impression formation, then we would expect a smaller influence of skin smoothness in the presence (vs. absence) of blemishes.
We tested this predicted interaction by orthogonally manipulating the two skin properties in a 2 (unsmoothed vs. smoothed skin) Â 2 (unblemished vs. blemished skin) design. We focused on judgments of attractiveness as we found effects for both smoothness and blemishes on this trait in Study 1. In line with our previous findings, we predicted that compared to the unmanipulated baseline faces, the smoothed faces would be perceived as more attractive, the blemished faces would be perceived as less attractive, and that the effect of blemishes would be stronger than the effect of smoothness. Crucially, we predicted that the positive effect of smoothness would be weaker when skin blemishes were also present. We further predicted that skin blemishes would lead to lower attractiveness ratings for both unmanipulated and smoothed faces.
Next to testing for a potential interaction between smoothness and blemishes, the current study included several notable improvements. We tested our hypotheses using a new and larger set of images drawn from the Chicago Faces Database (Ma, Correll, & Wittenbrink, 2015) with targets that were on average older. Skin unevenness increases with age (Fink, Grammer, & Matts, 2006) and smoothing might therefore have a stronger effect for older individuals. Thus, using this new set of older targets not only allowed us to test if our findings from Study 1 generalize to a different image set, but it also provided a stronger test of our hypothesis that blemishes have a stronger effect than smoothness.

Methods
Participants. We aimed for a minimum sample of 160 participants, which would provide 40 independent judgments for each face. This sample size is in line with previous studies that manipulated facial appearance and followed a similar experimental design (Rudert, Reutner, Greifeneder, & Walker, 2017). We recruited 204 MTurk workers. The median completion time was 5.5 minutes, and participants were paid $1. In line with our preregistered exclusion criteria, we excluded 35 participants (17.16%) who indicated having seen one or more face stimuli in a previous study (and who could have thus been aware of our manipulation) and 4 participants (1.96%) who explicitly stated that the images looked artificially generated or digitally altered. This resulted in a final sample of 164 participants (64.4% females; M age ¼ 35.12, SD age ¼ 10.50).
Materials. We selected 14 male and 14 female individuals from the Chicago Face Database . The accompanying data set contains age and attractiveness ratings for all targets. Each image was shown to 20 to 131 (M ¼ 43.74) participants who rated targets on different dimension (for more details, see Ma et al., 2015). Targets' average estimated age ranged from 22 to 43 years (M age ¼ 29.78, SD age ¼ 5.34). All individuals were White, displayed a neutral facial expression, and were photographed from the front. We ensured that there were no significant gender differences in estimated age, t(25.7) ¼ 1.16, p ¼ .26, or attractiveness, t(20.7) ¼ 0.58, p ¼ .57, in our sample of targets. The images were cropped to an oval shape measuring 480 Â 600 pixels. Four different versions of each face were created using the same image manipulation technique as in Study 1 (for a total of 112 stimuli): an unmanipulated baseline version, a smoothed version, a blemished version, and a smoothedblemished version (see Figure 3). For the smoothed-blemished version, we used each target's smoothed version and added the same pattern of skin blemishes that was used to create the blemished version.
Procedure and design. Four stimulus sets were created. Each set contained all faces, but which version of the face was included differed between sets. Each set contained seven faces per facial skin condition. As a high number of individuals with skin blemishes might raise suspicion among participants, we also included 12 additional unmanipulated faces that acted as filler items. Participants only rated one set. Thus, all participants were assigned to a 2 (skin smoothness: unsmoothed vs. smoothed) Â 2 (skin blemishes: unblemished vs. blemished) design, with skin smoothness and skin blemishes as within-subject factors. After providing written informed consent, participants were shown one face at a time in a random order and were asked to rate the target's attractiveness on a scale from 1 (not attractive at all) to 9 (extremely attractive). Participants showed significant consensus in their attractiveness ratings (ICC mean ¼ .373, all ps < .001).

Results
We again estimated linear mixed-effects regression models with participants and faces as random effects. Our first goal was to test if the findings from Study 1 replicated with a different set of targets. Regressing attractiveness ratings on skin smoothness (0 ¼ unsmoothed, 1¼ smoothed) and skin blemishes (0 ¼ unblemished, 1¼ blemished) showed a negative effect of blemished skin, b ¼ À0.450, SE ¼ 0.039, t(4,372.0) ¼ 11.68, p < .001, 95% CI [À0.528, À0.371], and a positive effect of smoothed skin, b ¼ 0.260, SE ¼ 0.039, t(4,372.0) ¼ 6.77, p < .001, 95% CI [0.193,0.340]. When compared to the baseline faces, the blemished faces were perceived as less attractive, and the smoothed faces were perceived as more attractive. We found a significant difference between the effect of blemished skin and the effect of smoothed skin, z ¼ 3.49, p < .001, showing that the effect of blemished skin on attractiveness ratings was significantly stronger than the effect of smoothed skin. Thus, we successfully replicated our findings from Study 1.

Discussion
Study 2 shed more light on the mutual influence of skin smoothness and blemishes on perceptions of attractiveness. We found that skin smoothness positively influenced attractiveness ratings, but that this effect was substantially smaller when targets also displayed skin blemishes. Blemishes negatively influenced perceived attractiveness for individuals with unmanipulated and smoothed skin. This pattern of results is in line with our argument that blemishes are a more salient cue in impression formation than skin smoothness. Using a larger and on average older sample of targets, we were also able to replicate the findings of our previous study. Although both smoothing and adding blemishes influenced perceptions of attractiveness (for both male and female targets), the negative effect of blemished skin was again significantly stronger than the positive effect of smoothed skin.

General Discussion
We investigated the influence of facial skin texture on impression formation by comparing trait judgments of individuals with facial skin blemishes and smooth skin against an unmanipulated version. Building on prior studies showing that people are particularly sensitive to cues connoting poor health (Zebrowitz & Rhodes, 2004), we predicted that the negative influence of facial skin blemishes would be stronger than the positive influence of smoothed skin. Results from our pretest confirmed that facial skin texture influenced perceptions of health. Individuals with blemished skin were seen as less healthy, whereas individuals with smoothed skin were seen as healthier compared to individuals with unmanipulated skin. In line with our prediction, the negative effect of blemished skin on health judgments was significantly stronger than the positive effect of smoothed skin. Study 1 showed that, compared to an unmanipulated baseline version, individuals with skin blemishes were perceived as less trustworthy, less competent, and less attractive. Although individuals with smooth skin were not perceived as significantly more trustworthy or competent compared to the baseline version, we did find that they were perceived as more attractive. However, the negative effect of blemished skin on attractiveness ratings was again significantly stronger than the positive effect of smoothed skin. This pattern was replicated in Study 2 with a different set of faces. Moreover, our second study showed that while smoothed skin had a positive impact on perceived attractiveness, this effect was reduced by almost half when individuals also displayed skin blemishes. In sum, our results demonstrate the salient role of skin blemishes in the formation of trait judgments from facial features.
The present findings are consistent with the functional view of trait impressions from faces. Perceived trustworthiness and competence represent evaluations of an individual's threat potential (Oosterhof & Todorov, 2008). In a similar vein, perceived attractiveness is a proxy for an individual's mate value and determines who is sought out as a sexual partner (Rhodes et al., 2005). In other words, trait impressions from faces are proxies for underlying approach-avoidance tendencies. Negative judgments of individuals with skin blemishes may thus reflect the avoidance response triggered by the detection of a potential disease threat.
Our interpretation of the results converges with previous findings showing that even benign physical irregularities (e.g., a port wine stain) can trigger avoidance (Houston & Bull, 1994;Ryan et al., 2012). This can be explained by people's sensitivity to cues connoting poor health and the potential presence of an infectious disease (Schaller et al., 2015). Given the high cost of engaging with sick individuals, even cues that resemble symptoms of an infectious disease can trigger an avoidance response aimed at shielding the individual from contracting the disease. We add to this literature by demonstrating that people's sensitivity to disease cues not only guides behavioral responses toward individuals (e.g., by increasing physical proximity; Houston & Bull, 1994) but also influences social perception (see also, van Leeuwen & Petersen, 2017). In addition, we show that this response is triggered not only by relatively rare facial irregularities such as a port wine stain but also by subtle skin blemishes that can result from common skin conditions.
Our findings support the notion that an individual's perceived health is an important determinant of attractiveness perceptions (Jones et al., 2004). Low perceived health may indicate the presence of a disease or a weak immune system, which are both undesirable characteristics for potential mates (Rhodes et al., 2007;Zebrowitz & Rhodes, 2004). We find that individuals with skin blemishes are seen not only as less healthy but also as less attractive. Across our three sets of faces in our pretest and Study 1, we find large correlations between perceived health and perceived attractiveness (r ¼ .67; see supplemental materials for full correlation matrices). In fact, even though trustworthiness, competence, and attractiveness represent core dimensions of trait impressions from faces and are assumed to be relatively independent (Sutherland et al., 2013), we found large correlations between them (rs ¼ .60-.81). Therefore, it is unclear whether there is a direct effect of facial skin blemishes on each trait or whether blemishes primarily influence one trait (e.g., health) which, in turn, influences perceptions of other traits (e.g., attractiveness). Our theoretical framework would predict that more negative trait impressions of individuals with skin blemishes are driven by the motivation to avoid potentially sick individuals. Future studies could test this prediction by investigating whether perceived health mediates the influence of blemishes on perceived trustworthiness, competence, and attractiveness. Prior work has already shown that perceptions of health account for a substantial part of the association between facial redness and attractiveness judgments (Pazda, Thorstenson, Elliot, & Perrett, 2016;Thorstenson, Pazda, Elliot, & Perrett, 2017).
People's sensitivity to cues of poor health likely extends beyond the relative influence of blemished and smooth skin. For example, the previously mentioned work on facial redness also showed that the effect of decreased redness was stronger than the effect of increased redness (Pazda et al., 2016;Thorstenson et al., 2017). Relatedly, Park et al. (2012) found that individuals high on pathogen disgust perceive relatively unattractive people as even more unattractive than individuals low on pathogen disgust. However, pathogen disgust was unrelated to attractiveness ratings of relatively attractive people, suggesting that concerns about pathogens selectively influence reactions to seemingly unfit or unhealthy individuals. Building on these findings, we would suggest that other facial cues of health should follow the same pattern, with features indicating poor health exerting a stronger influence than features indicating good health. In addition, the influence of cues to poor health might be moderated by individual differences in pathogen concern (Duncan, Schaller, & Park, 2009).
Although we were able to demonstrate our main findings in two image sets that differed in nationality and age and that included both male and female targets, more research is needed to explore the generalizability of our results. First, skin unevenness due to wrinkles or irregular pigmentation increases with age (Fink et al., 2006) and the effect of skin smoothing, which erases these irregularities, might vary as a consequence. In our second study, we used images of targets that were on average older and that had a wider age range than targets in our first study. Comparing the effect of smoothed skin on attractiveness ratings of targets between Study 1 (20-30 years old; M age ¼ 23.81, SD age ¼ 3.67) and Study 2 (22-43 years old; M age ¼ 29.78, SD age ¼ 5.34) showed no significant difference (Study 1: b ¼ 0.295, SE ¼ 0.070; Study 2: b ¼ 0.260, SE ¼ 0.039; z ¼ 0.44, p ¼ .66). However, our studies differed on many other aspects and a more direct test of the influence of skin smoothness across the entire age range is needed to address this question.
Second, both studies reported here featured Caucasian targets that were rated by participants from Western societies (the Netherlands and the United States). Given recent evidence for cultural differences in impression formation (Han et al., 2017;Sutherland et al., 2017), our findings should be replicated using more diverse sets of targets and raters.
Third, future research should also consider different aspects of facial skin texture. As we have stated before, smooth skin demonstrates the absence of several possible irregularities such as blemishes, wrinkles, uneven pigmentation, large pores, or birth marks. Here, we focused on the role of blemishes due to people's sensitivity to cues connoting the potential presence of an infectious disease. It remains to be tested whether other skin properties similarly influence trait impressions. Relatedly, it could be argued that adding blemishes influenced not only skin texture but also skin color. Even though blemishes were only present on some parts of the face, the overall facial redness of the blemished faces was higher compared to the unmanipulated baseline faces. However, facial redness has been linked to more positive judgments of health and attractiveness (Pazda et al., 2016;Thorstenson et al., 2017), whereas we found more negative judgments of blemished faces. Thus, even though changes in facial redness might have contributed to the observed effects, these changes cannot explain why blemished faces were perceived more negatively. Ultimately, larger samples of faces that represent the entire spectrum of variation on different facial cues need to be evaluated on multiple trait dimensions in order to understand the influence of different face properties on trait perceptions. Furthermore, statistical approaches such as mediation analysis (Pazda et al., 2016;Thorstenson et al., 2017) or network analysis (Costantini et al., 2015) can aid in disentangling the interrelationships between different traits.
To conclude, the current research demonstrates that the presence of skin blemishes affects trait impressions from faces. Perceptions of trustworthiness, competence, and attractiveness reflect approach-avoidance tendencies and guide who is sought out as a sexual or social partner. Negative judgments of individuals with blemished skin might thus serve the function of preventing contact with potentially unhealthy individuals.