Saturday, July 27, 2013

Skin color and the menstrual cycle


 
The female torso visibly reddens towards the end of the menstrual cycle. Do men unconsciously pick up on this visual cue? (Figure from Edwards and Duntley, 1949)

 
Women vary in skin color over the menstrual cycle. From mid-cycle on, their skin steadily reddens because of an increase in blood flow that peaks in the day or two preceding menstruation.This cyclical “blushing” mainly affects the torso:

[…] these cyclic variations in blood flow were observed over the entire trunk and at least the upper parts of the limbs. There is suggestive evidence that the face and the hands and feet may share in these changes. (Edwards and Duntley, 1949)

Facial skin, especially around the eyes, shows a similar cyclical change, according to two questionnaire surveys: 

[…] about half the women questioned had some increase in skin pigmentation, which was noted in every case in the latter days of the menstrual cycle and in some cases during menstruation also. The others showed no skin changes whatsoever.

[…] The site most commonly showing pigmentation changes was the skin around the eyes. Next most frequently affected were the areola of the nipple and the perioral skin. The forehead, axilla, and abdomen were affected in less than one-third of the "positive" subjects. (McGuiness, 1961) 

In answer to the questionnaire, 18 women (62%) consistently noticed darkening of the peri-ocular skin towards the end of the menstrual cycle, i.e. immediately prior to the onset of menstruation; of these, three also noticed darkening of the nipple areolae, two the forehead skin and one the peri-oral skin. (Snell and Turner, 1966)

Snell and Turner (1966) confirmed these observations by measuring the percentage of light reflected by facial skin, although the cyclical variation was rather small. Unlike the torso, the face doesn’t redden towards the end of the cycle. Instead, it becomes browner through increased melanocyte activity:

The results from the skin reflectance readings did not show any great changes. The readings obtained from the cheek and lower eyelid indicated that the melanin content of the skin in these regions tended to rise in the later part of the cycle in many of the women. 

[…] The melanocytes of the anterior abdominal wall skin over the linea alba showed no changing pattern of activity at different phases of the menstrual cycle.

[…] It was concluded that a proportion of normal women, especially dark-skinned brunettes, have darkening of the facial skin during the later days of the menstrual cycle and this mainly involves the peri-ocular skin. (Snell and Turner, 1966) 

Does this cyclical variation provide men with a means to assess female fertility? An unconscious means, to be sure. Pierre van den Berghe thought so, but I ignored his gentle prodding and avoided the subject, all the more so because a search of the ethnographic literature failed to turn up any awareness in any human society of this cyclical change. In contrast, many societies have been keenly aware that women are fairer-skinned and men darker-skinned, often to the point of making this sex difference an artistic convention (van den Berghe and Frost, 1986; Frost, 1988; Tegner, 1992).

One research team has tried to find out whether men pick up on this cyclical variation:

Here, in an initial pilot study, we test the hypothesis that changes in female facial skin coloration across the menstrual cycle could be one of the signals that men have adapted to in order to assess female fertility. Spectrophotometric measurements of the facial skin color of normally ovulating Caucasian women (aged 24–29 years) were collected in the late follicular and midluteal phase of their menstrual cycle. Facial images were also taken in both sessions and judged for attractiveness and health by a panel of German men (aged 16–37 years). In line with Roberts et al. (2004), our results show that men perceive women in the late follicular phase to be significantly more attractive and healthier than those in the midluteal phase. However, we did not detect any significant differences in objective measurements of skin color between the two phases. (Samson et al., 2011)

This study suffers from a few flaws. The authors measured skin reflectance on the forehead and the cheeks, yet these body sites are less involved in darkening and lightening of female skin over the menstrual cycle. It would have been better to measure skin reflectance around the eyes (although premenstrual peri-ocular darkening might have likewise been absent in the fair-skinned German participants). Better yet, this study should have focused not on the face but on the torso, since that body region is the one most affected by this cyclical variation. We should also keep in mind that men unconsciously use two different aspects of female pigmentation for gender recognition. One is the lighter skin of a woman’s face. The other is the higher contrast between facial skin color and eye/lip color (Russell, 2009; Russell, 2010; Porcheron et al., 2013; see also Dupuis-Roy et al., 2009). This contrast effect might be weakened by the premenstrual darkening of skin around a woman’s eyes.

A more recent study has corroborated that men prefer faces of ovulating women to those of premenstrual women (Bobst and Lobmaier, 2012). It concludes that subtle changes in face shape are responsible, although changes in skin color cannot be ruled out. In fact, if men can respond to such subtle changes in face shape, they should also be able to respond to changes in facial color that are no less subtle.

It may be worthwhile to take another look through the ethnographic literature. One of my wonderful commenters has pointed me to an article by a sociologist of Zambian origin, Mwizenge S. Tembo:

It is [with] the frequent circulation of the hormones, the increased flow of blood during ovulation, and especially during pregnancy that women in Sub-Saharan Africa may acquire a characteristic mild to quite remarkable red-orangeish glow to their skin. In fact an obvious tell-tell sign of being pregnant among married women and also among young girls who may have had sex out of wed lock, even when the pregnancy is not even physically visible, is the characteristic lightening of the skin-tone whether the woman is light or very dark. Among the Tumbuka, Chewa, Nsenga, and Ngoni people of Eastern Zambia, several terms are used to describe the state of being pregnant. “Ali ndi pakati” means that “the woman is in between”. Because the majority of women in African societies prior to modern medicine had very high deaths and faced danger during the birthing process, the woman was said to be literally “between life and death” or “living with uncertainty”. “Ali ndi mimba” means “the woman has a stomach” referring to the obvious bulging stomach of a pregnant woman. The most relevant term to this discussion is “ali ndi pathupi” which means “the woman has a body” (Salaun, 1969; Price, 1970) which refers to the characteristic light skin tone or the visible obvious glow the woman assumes when she gets pregnant. 

This light reddish skin is considered desirable by African men and may serve an adaptive purpose: “Among many other possible explanations, the most compelling may be that the lighter skin, even among the darkest of indigenous Africans, may have been a normal and natural biological marker and signal that the woman was very fertile.” Tembo is a fan of evolutionary psychology and may be indirectly echoing a meme that began with me and Pierre van den Berghe. Nonetheless, there may indeed be more awareness of this menstrual change in skin color than I had thought, particularly in settings where most variation in skin color is intra-ethnic.

Conclusion

When all is said and done, this research topic may still be ‘a bridge too far.’ Admittedly, a researcher should have little trouble finding out whether the premenstrual darkening of the eye area is a sexual turnoff for men. I’m sure it is—many women certainly seem to think so. But how would one determine whether this male response is hardwired or not? By measuring it as a function of testosterone levels? Finally, would such a hardwired mental algorithm shed light on other feelings towards skin color?

It might be more interesting to investigate how men respond to the premenstrual reddening of the female torso region. Recruitment of female participants would nonetheless be much more difficult, as would be the task of getting approval from the research ethics committee. There’s also the little matter that this premenstrual ‘blushing’ is visible only in light-skinned women. Conversely, premenstrual darkening of the eye area is visible mainly in darker-skinned women. 

References

Bobst, C., and J.S. Lobmaier. (2012). Men's preference for the ovulating female is triggered by subtle face shape differences, Hormones and Behavior, 62, 413-417.
http://www.ncbi.nlm.nih.gov/pubmed/22846725

Dupuis-Roy, N., I. Fortin, D. Fiset, and F. Gosselin. (2009). Uncovering gender discrimination cues in a realistic setting, Journal of Vision, 9(2), 10, 1–8.
http://journalofvision.org/9/2/10/

Edwards, E.A. and S.Q. Duntley. (1949), Cutaneous vascular changes in women in reference to the menstrual cycle and ovariectomy, American Journal of Obstetrics and Gynecology, 57, 501-509.

Frost, P. (1988). Human skin color: a possible relationship between its sexual dimorphism and its social perception, Perspectives in Biology and Medicine, 32, 38-58.

McGuiness, B.W. (1961). Skin pigmentation and the menstrual cycle, British Medical Journal, 2, 563.
http://europepmc.org/articles/PMC1969464?pdf=render

Porcheron, A., E. Mauger, and R. Russell (2013). Aspects of facial contrast decrease with age and are cues for age perception. PLoS ONE 8(3): e57985
http://www.plosone.org/article/info%3Adoi%2F10.1371%2Fjournal.pone.0057985

Russell, R. (2010). Why cosmetics work. In Adams, R., Ambady, N., Nakayama, K., & Shimojo, S. (eds.) The Science of Social Vision. New York: Oxford.
http://public.gettysburg.edu/~rrussell/Russell_SocialVision_cosmetics_chapter.pdf

Russell, R. ( 2009). A sex difference in facial contrast and its exaggeration by cosmetics, Perception, 38, 1211-1219
http://public.gettysburg.edu/~rrussell/Russell_2009.pdf

Samson, N., B. Fink, and P. Matts. (2011). Does a woman’s skin color indicate her fertility level? Preliminary findings, Swiss Journal of Psychology/Schweizerische Zeitschrift für Psychologie/Revue Suisse de Psychologie, 70(4), 99-202.
http://psycnet.apa.org/journals/sjp/70/4/199/

Snell, R.S. and R. Turner. (1966). Skin pigmentation in relation to the menstrual cycle, Journal of Investigative Dermatology, 47, 147-155.
http://www.nature.com/jid/journal/v47/n2/full/jid1966119a.html

Tegner, E. (1992). Sex differences in skin pigmentation illustrated in art, The American Journal of Dermatopathology, 14, 283-287.
http://journals.lww.com/amjdermatopathology/Abstract/1992/06000/Sex_Differences_in_Skin_Pigmentation_Illustrated.16.aspx

Tembo, M.S. (2010). The Rediscovery of the Beautiful Woman in African Societies. Eurocentric Destruction of Indigenous Conceptions: the Secret Rediscovery of the Beautiful Woman in African Societies.
http://people.bridgewater.edu/~mtembo/menu/articles/AfricanBeautyRevisedMarch162010.pdf
 
van den Berghe, P. L. and P. Frost. (1986), Skin color preference, sexual dimorphism, and sexual selection: A case of gene-culture co-evolution? Ethnic and Racial Studies, 9, 87-113.
http://www.tandfonline.com/doi/abs/10.1080/01419870.1986.9993516

Vargas-Guadarrama, L. (1971). Pigmentation cutanée et cycle menstruel, Paris, Université Paris VII, Thèse de doctorat.

10 comments:

Sean said...

rimates may have evolved color vision not to find the ripest, tastiest fruit but rather to detect that telltale blush on someone else's rump

Anonymous said...

This does all sound very plausible.

"Better yet, this study should have focused not on the face but on the torso"

I was thinking the same - in particular i was thinking baboon ass signalling for primates that walk upright.

This would also tie in with women showing more flesh when they're ovulating.

"There’s also the little matter that this premenstrual ‘blushing’ is visible only in light-skinned women."

I dunno. I can tell when black women blush it's just harder - for me anyway. Maybe men from darker-skinned populations notice it better?

Anonymous said...

On a darker note there's also

http://www.huffingtonpost.com/hal-herzog/why-are-rape-victims-more_b_1823152.html

"Twenty six of the women who had been raped became pregnant -- a pregnancy rate of 6.42 percent. (This increased to 8 percent when adjusted for contraceptive use.)"

"Among the "regular cyclers," a woman's chances of conceiving ranged from a high of 9 percent if they had sex on day 13 of their cycle to 0 percent when they were having their period."

"In short, women are at least twice as likely to conceive as a result of rape than by consensual sex."

Or women are more likely to be attacked when they're ovulating.

Sean said...

It is in a male's interest to mate with females who are ovulating, but not just with one female. In a monogamous mating system the female has concealed ovulation to encourage the male to stick close all the time, instead of chasing after any ovulating female.

A monogamous man's reproductive fitness would would be maximized by mating with his woman when she was ovulating. When the male has to go on hunting trips he does not want to do that when the woman is ovulating, because there would be a danger of being cuckolded. So men are selected for perceiving subtle signs of ovulation in the skin tone, smell and voice of women as sexually attractive.

Women in the modern world use pseudo-signs of ovulation to maximise their attractiveness. I believe there is even a study that found they were much more likely to wear pink or red when ovulating.

Anonymous said...

What certain sub-Saharan African regions would consider "light skin" is considered dark in the rest of the world (the deep caramel, golden brown skin tone).

Anonymous said...

Maybe become redder in the skin color around the torso near the menstrual cycle is an attraction cue.

Anonymous said...

"What certain sub-Saharan African regions would consider "light skin" is considered dark in the rest of the world"

Yes but there might be a consistent pattern *within* each ethnic group.

.

"Maybe become redder in the skin color around the torso near the menstrual cycle is an attraction cue."

That strikes me as a highly plausible variation on baboon-ass.

Anonymous said...

Does the use of contraceptives tie with the sudden preferential flip for tanned skin instead of light skin in women in the west? If contraceptives stop the ruddy effect, sun tanning might be a behavioral adaptation to make up for the lessening of sexual appeal.

- Inquisitor

Anonymous said...

"lightly pigmented areolae, indicative of youth and nubility, should receive most visual attention and be rated as most attractive, but images with dark and medium areolar pigmentation are rated as more attractive than images with light areolae"

http://www.ncbi.nlm.nih.gov/pubmed/20169468

Anonymous said...

"There’s also the little matter that this premenstrual ‘blushing’ is visible only in light-skinned women. Conversely, premenstrual darkening of the eye area is visible mainly in darker-skinned women."

And what do you base this on? Your citation of Tembo's paper certainly doesn't indicate that. You even admit yourself you couldn't find any references to this in any human society yourself, but apparently, in african ones, this is widely attested to. This reminds of the claims dark skinned people don't show visible blushing, which I imagine even you're aware is false. With regards to the "darkening of the eye area", the only evidence you've presented is the reference to "dark skinned brunettes", a terribly vague term that would most likely mean southern european women.