Is Tanning Even Attractive?

With summer arriving in the northern hemisphere, the eternal questions of “how much sun” and “to suncreen or not to suncreen” are back in season. Through recent population studies, the pendulum seems to be swinging back in the direction of more sun is better. We know that vitamin D is important, and that the best way to get it is through exposing our skin to sunlight. Indeed, it seems like the case for sun wins hands down. Not only does that seem to be the case from the medical realm, but it’s become ingrained in our very notions of beauty. Or has it?

Skin Color and Beauty

Tanning seems like an obvious case for the social constructivists to prove, once and for all, that our conceptions of beauty are products of immersive socialization. We hear the arguments about pasty skin being attractive in times when the bourgeoisie lounged indoors counting money and adjusting powdered wigs while the proletariat labored in the fields. The story goes that having a tan was a dead giveaway that one was a low-status individual. Of course, we’ll momentarily ignore that this narrative tends to leave out the part that darker skin also carries varying racist overtones. In any case, the social constructivist points to modern society in which very few people know farmers, let alone have ever labored on a farm.

Since the cultural milieu has shifted away from an agrarian dominated context, the stigma of sun-induced dark skin has lifted. With the swing in culture, the attractiveness pendulum has swung the other way as well. This is evidenced by the widespread obsession for the “healthy glow” gained from spending time in the sun. The narrative has subsumed this observation and explained that, in fact, tans are now a signal of bourgeois status because, clearly, proletarian office drones don’t have expendable leisure time to spend laying around on the beach. Doesn’t the story fit together so nice and commonsensically!?

The Color Theory of Tanning

Design nerds, get out of CMYK, RGB, or HSV mode for a second. Scientists working with human visual perception use the (aptly named) Lab color space to most accurately replicate the way our eyes process inputs. For non-uber design geeks, Lab represents a 3-axis color system represented by L, a, and b. The L-axis describes the spectrum from Lightness-darkness. The a-axis describes the spectrum from red-green. The b-axis describes the spectrum from yellow-blue. I’ll try to just use “red-green”, et cetera when possible, but the shorthand is woven into all of the charts and quotes from the papers.

Sun tanning primarily changes values along two axes, the L (lightness) and b (yelowness). The increased melanin resulting from tanning results in a decrease in lightness and an increase in yellowness (Stamatas, et al. 2004). Therefore, we can make the simple prediction that if people indeed prefer tans resulting from the sun, we should see a preference for relatively darker skin and relatively yellower skin.

Though tanning has now been popular in Western culture for decades (Melia & Bulman. 1995), studies haven’t isolated the color variables necessary to test the “tan is beautiful” hypothesis until now. Ian Stephen, PhD and colleagues presented research in the journal Evolution and Human Behavior that address this question. Their study involved a group of white UK-based students who rated white faces, and a group of black South African students who rated black faces. The data from both groups was similar, and both are shown below…

South African rater’s adjustments of black face and similar results of Scottish rater’s of white face

The picture on the left is an example of the extremes available in the adjustment along both axes for the black faces. Note that the UK raters were rating a different face (not shown here).

Both cohorts show a strong grouping to the same quadrant. However, the quadrant selected was not what we’d expect if the “tan is beautiful” hypothesis was true. We should expect to see both groupings shifted to the top-left quadrant. It turned out that yellowness was perceived as a positive indicator of health, but relative lightness was preferred over darkness. Based on these data, we must conclude that the “tan is beautiful” hypothesis is incorrect.

The social constructivist narrative is also refuted by these findings. Since tanning behaviors are heavily influenced by socialization, we would expect to see a preference in the data for darker relative skin tones. Further, a constructivist explanation seeking to simultaneously explain pro-darker skin tanning in white individuals AND pro-lighter skin attitudes in black individuals would require the data to show the South African data to be in a different quadrant than the UK data. These data refute the existence of a culturally imparted ideal of beauty or health that can be plotted on the spectrum from lightness-darkness.

Since the “tan is beautiful” hypothesis and social constructivist arguments both fail, what explanations are we left with?

The Pasty Veg*ns Are Sexier than Sun-Bathed Carnivores Hypothesis

Enter the carotenoid. Sun exposure isn’t the only thing that affects skin color. Significant consumption of [carotenoid-containing] plant matter also impacts coloration. Stephen, et al conducted a study (results in the same paper) measuring the relationship in fruit and vegetable intake with skin color and the change in skin color resulting from carotenoid supplementation. They found that both supplementation and fruit and vegetable intake correlated with, and increased skin yellowness as measured by spectrophotometer. Further, the measured colorations were inconsistent with coloration changes from melanin (sun tan) and hemoglobin. The carotenoid coloration data fit with the results above; namely, an increase in yellowness without an decrease in lightness. This lead to another study (also reported in the same paper).

This time, rather than isolate the axes for lightness and yellowness, they provided raters with the ability to optimize for health along one axis corresponding to melanin coloration and another corresponding to carotenoid coloration. The results…

Scottish raters’ adjustments of Caucasian face. Melanin on the vertical axis. Carotenoid on the horizontal.

In a post about the same study on his blog Primal Wisdom, Don Maetz provides a heading “Carotenoid Complexion and Sun Tan Not Mutually Exclusive”. While that is literally true, it is also possible that the perception of health signaled by carotenoids and sun tans are mutually exclusive. In fact, that is what the cumulative data in Stephen, et al seems to indicate.

As the preceding image shows, when given the option to specifically optimize the appearance of health for melanin and/or carotenoids, raters unanimously preferred higher levels of carotenoid, but were almost equally mixed in preferences for melanin coloration. This adds support to the refutation of the “tan is beautiful” hypothesis, and opens the door for the “pasty veg*ns are hot” hypothesis.

Methodology

The usability of data in similar previous studies has been questioned on the grounds that giving raters the choice between two options on each axis, then asking them to choose between them, is prone to errors. Stephen, et al first narrowed the image samples to ranges that might be seen in normal populations, then allowed 13 variance points along each axis. Rather than showing all at once, raters were asked to adjust the spectrum up or down to optimize the appearance of health. When plotted across both axes, this results in 39 possible selections. This seems sufficient, but I’m not sure why they didn’t allow infinite adjustments along each axis.

Other criticisms have been made that the use of Photoshop® does not provide an image representative of real-world faces. However, it’s difficult to provide a wide range of skin tones for one individual with photographic accuracy. Surely, using different individuals with different skin tones would introduce myriad variables that would render coloration assessments useless. So while there is some validity to this line of criticism, I find it rather thin.

Criticisms/Improvements

• I’m not sure that South Africa’s history makes it the best choice for disentangling variables concerning race-based perceptions. So while I do think the method employed limits cultural influence somewhat, I’d like to see the study done where the two countries involved weren’t formerly linked via colonization. Also, the level to which South African college students are subject to “Westernization” is difficult to know.
• Since individuals’ colorations were tested before and after carotenoid supplementation, it would have been nice to see ratings of photos of this cohort before and after. Many other variables have the potential to spoil the results, but the hard parts of that experiment were mostly done by default.
• I don’t like celery.

Tanning Obsession: Evolutionary Misfire

Based on this research, I would suggest that visually perceivable results of carotenoid consumption were a reliable signal of health, and that preference is a serious candidate for positive selection that continues to influence our perceptions of health and beauty today. It is difficult to disentangle how much of this selection pressure may have been influenced by direct benefits to health and reproduction, and how it may also be an indirect signal of resource gathering ability. The data support the former…

“Carotenoids are associated with immunocompetence anddisease resistance in humans. Supplementation beneficiallyaffects thymus gland growth in children and increases T-lymphocyte number andactivity in healthy adults. Carotenoid levels become reduced in individuals with HIV and malaria, and in individuals with elevated levels ofserum α1-antichymotrypsin.”

…but the indirect role in sexual selection is a question for another day. For now, chalking up the motivation toward sun tans as an evolutionary misfire seems reasonable. When given the option, raters prefer carotenoid pigmentation to melanin. However, when not given a choice…

“In the single-pigment transforms, all faces were increasedin carotenoid and melanin color to improve healthy appearance. No effects of face sex or participant sex, or theirinteraction were found. Participants increased melanin and carotenoid color more in faces that were initially low in b*. Initial L* and a* values had smaller effects. Participants increased carotenoid more than melanin coloration.”

This demonstrates that the yellow gained through tans somewhat outweighs the darkening that comes along with it. Thus, “yellower is better” and “lighter is better” do not appear to be equal in heuristic value and could signal other things not considered here.

Application

My current interpretation of the health implications is that a veg*n diet is inferior to a paleo diet in important categories. At the same time, strictly carnivore interpretations and/or meat & potatoes interpretations of the paleo diet seem to be inferior to veg*n diets with respect to healthy carotenoid levels. For me, that means taking the best of the veg*n and paleo approaches and eliminating the worst of both approaches. Sure, you paleo-leaning veg*ns out there can disagree, but the meat & plant paleo camp will have better looking bodies. Sure, you anti-plant-matter-leaning paleos out there can disagree, but the veg*n-leaning paleos will have better looking skin. So… do you want to be right, or do you want to be healthy and hot?

Sun exposure appears to be best used as a tool for optimal levels of vitamin D and secosteroids, not a shortcut to health or hotness. Don’t argue with me, take it up with the data. You should definitely get some sun, but you probably can’t use color as an indicator that you’ve reached an optimal level.

Summary (Just Do This)

• If health is your goal, eat a ton of carotenoid-dense fruits and vegetables.
• If looking healthy is your goal, eat a ton of carotenoid-dense fruits and vegetables.
• Get sun for the vitamin D and the secosteroids.
• Don’t get sun just for the color.
• Oh, you should probably subscribe so you don’t miss adding another dimension to the equation with the findings from this study: “Who is the fairest of them all? Race, attractiveness and skin color sexual dimorphism“

References
Glenn, E. N. (2008). Yearning for lightness: transnational circuits in the marketing and consumption of skin lighteners. Gender & Society, 22, 281–302. *also appears as a chapter in The Kaleidoscope of Gender: Prisms, Patterns, and Possibilities‘  (2010).

Melia, J., & Bulman, A. (1995). Sunburn and tanning in a British population. Journal of Public Health Medicine, 17, 223–229.

Stamatas, G. N., Zmudzka, B. Z., Kollias, N., & Beer, J. Z. (2004). Non-invasivemeasurements of skin pigmentation in situ. Pigment Cell Research, 17, 618–626.

Stephen, Ian D., Vinet Coetzee, and David I. Perrett. “Carotenoid and melanin pigment coloration affect perceived human health.” Evolution and Human Behavior 32, no. 3 (May 2011): 216-227. [full-text pdf]