Eyelash length attractiveness across ethnicities

Pazhoohi and Kingstone¹ recently discovered that as eyelashes lengthen, faces are perceived to be more attractive. But only up to a point, beyond which the perceived attractiveness of faces begins to fall with increasing eyelash lengths. In the original work that yielded this inverted-U function, the female faces that were rated for their attractiveness were white skinned. In the present study we asked if the inverted-U function occurs for faces of other skin colors/ethnicities. And if perception varies systematically for observers of different ethnicities.

The results showed that all Asian, Black and White participants rated different ethnicities of Indian, Asian, Black, and White female faces in a similar fashion, regardless of eye colour, yielding an inverted-U relationship. This suggests a general inverted-U function for the perceived attractiveness of faces that mirrors the optimal length for eyelashes in terms of their evolutionary development—balancing eye protection with vision. Amador et al.² identify the optimal eyelash length at about one-third the eye width (L/W ratio of 0.35 ± 0.15). Our results are convergent with this ratio. They also suggest, however, some variation across the ethnicities on the most preferred ratios. In the present study the preferred L/W ratio ranged between 0.25 to 0.40 with slight differences emerging as a function of an observer’s ethnicity. For example, Asian participants rated Asian faces as the most attractive for ratios 0.20–0.35, while Black participants preferred Asian faces for ratios 0.25–0.40.

A difference for the highest attractive ratios were also found to vary as a function of the image itself. Results showed that ratings of Black women’s eyelashes by all Asian, Black and White participants were slightly skewed toward a larger ratio than the other faces (see Fig. 2). Previous research has indicated differences in perception of attractiveness as a function of skin color^26,27, and facial racial physiognomy and characteristics^11,27,28. While the source of this skew is presently unknown, it could reflect a change in perceptual sensitivity to eyelash length with skin colour. In other words, the slight difference found in the most attractive eyelash length among ethnicities in this study might be due to the color contrast between black eyelashes and skin color of ethnicities, with Black faces providing less contrast. Nonetheless, it might have been expected that individuals would rate the most attractive eyelash length for Indian faces higher compared to White and Asian faces, as they would provide less contrast with the skin color. However, this was not the case, which raises the need for future research to combine incremental skin color variations from light to dark with different eyelash lengths to examine their impact on the perception of attractiveness.

As for the least attractive eyelash length, the results dovetail with those of Pazhoohi and Kingstone¹, where female faces with no eyelashes and very short eyelashes were the perceived to be the least attractive. Similarly, all ethnicities rated faces of every ethnicity with no and very short eyelash length as the least attractive compared to the other eyelash lengths.

The results of this study also showed that men and women perceive the effect of eyelashes on attractiveness in a similar manner, regardless of the ethnicity of the participants or the stimuli. While there are sex differences in perception of facial attractiveness perception at neural and behavioral levels [^18,29; cf.³⁰], the convergence across the sexes in the present study speak to the robustness of the present effect. This point is supported further by the fact that we obtained the same inverted-U pattern whether participants were asked to rank the attractiveness of the faces against one another as in Ref.¹ or to numerically rate each face’s attractiveness individually as in the present study. In sum, the inverted-U function generalizes across tasks, populations, and stimulus types.

The current study is not without limitations. While using the 3D-generated stimuli instead of actual faces decreased the ecological validity of this study, on the other hand, it provided the possibility to control for other aspects of the stimuli, such as hair color and style, facial ratios, stimuli exposure and brightness, etc. To increase ecological validity, future research may choose to use actual faces for investigating the effect of eyelash length on attractiveness perception. Another limitation of the current study is the use of only female faces which constrains the generalizability of the effect. While Pazhoohi and Kingstone¹ reported a similar inverted-U function for male faces—albeit skewed for shorter ratios—future research might choose to include male faces from different ethnicities. Moreover, using a single identity for generating different ethnicities is another limitation of the generalizability of this study, as one might argue that this specific pattern of results might have arisen from the particular combination of facial features.

The results of the current study, along with those of Pazhoohi and Kingstone¹, are partially supportive of a previous study conducted by Adam³¹ on the attractiveness of the eyelash lengths. Specifically, Adam³¹ created eyelashes on stimuli as twice the length of the original version, as well as making them fuller and darker. Comparing the attractiveness of the faces with the manipulated eyelashes to the original ones, she found that longer eyelashes contribute to higher attractiveness ratings. The Adam’s study was limited in the ranges of the eyelash lengths, most specifically in the upper range, which is resolved by the current study as well as that of Pazhoohi and Kingstone¹. While using a more diverse sample of faces (in terms of sex, ethnicity, and age) of real people smiling, might have resulted in more generalizability of Adam’s study³¹, it might have also left many confounding variables in the stimuli compared to the current study.

The hypothesis presented in this study was based on research revealing that very long and short eyelashes can indicate congenital and noncongenital diseases from health and genetic perspectives. We argued that attractiveness of eyelash length should be considered from an adaptive evolutionary viewpoint which posits that attractiveness is an honest indicator of health and genetic quality^3,4. However, the current study was limited by only measuring the attractiveness of eyelash length. An outstanding and substantive question is whether health, broadly construed, is a critical factor, or even the critical factor. To address this systematically, future research might include whether and how perception of health interacts with attractiveness ratings in this regard. While Adam³¹ has provided preliminary evidence on this issue by showing that shorter eyelashes are considered less healthy, it is an open question as to whether health is the factor that is driving the inverted-U function we observed for attractiveness. Nonetheless, the findings of the current study add to the previous research that has shown a correspondence between attractiveness and fitness for other features such as waist to hip ratio³², hair length³³, breasts³⁴, and scleral colour³⁵. Finally, the inverted-U shape function of attractiveness ratings might also suggest a preference for typicality where an optimum eyelash length matches (a) the typical or average length of the population and/or (b) the typical or average length experienced by individuals. Were one to garner reliable data on these two matters, one might tease apart the issue by finding, for example, that attractiveness ratings differ between ethnicities but measurements or typicality ratings do not; an outcome that would suggest that attractiveness ratings are not driven by typicality. An alternative approach would be to experimentally manipulate the base rate information on eyelash lengths in different populations and cross that with individuals being exposed to different frequencies of eyelash lengths. Again, if attractiveness ratings differ between ethnicities but measurements or typicality ratings do not, then the outcome would suggest that attractiveness ratings are not driven by typicality.

The current study has revealed that regardless of the sex or ethnicity of an observer, the effect of eyelash length on the perceived attractiveness of a women’s face follows an inverted-U function, with attractiveness rising then falling with increasing eyelash length. Critically, this pattern is observed for depiction of faces of different ethnicities (and eye colour). Collectively, the data dovetail with the view that the optimum eyelash length evolved to maximum protect and facilitate vision. As such, deviations from that optimum are perceived to be less attractive as they may serve as signals of ill health. This effect is robust across different forms of task and measurement. Nevertheless, the effects are not absolute, with the preferred range varying at times with the ethnicity of the observer or the image.