Abstract
Red facial coloration is an important social cue in many primate species, including humans. In such species, the vasodilatory effects of estradiol may cause red facial coloration to change systematically during females' ovarian cycle. Although increased red facial coloration during estrus has been observed in female mandrills (Mandrillus sphinx) and rhesus macaques (Macaca mulatta), evidence linking primate facial color changes directly to changes in measured estradiol is lacking. Addressing this issue, we used a longitudinal design to demonstrate that red facial coloration tracks within-subject changes in women's estradiol, but not within-subject changes in women's progesterone or estradiol-to-progesterone ratio. Moreover, the relationship between estradiol and facial redness was observed in two independent samples of women (N = 50 and N = 65). Our results suggest that changes in facial coloration may provide cues of women's fertility and present the first evidence for a direct link between estradiol and female facial redness in a primate species.
Highlights
It has been assumed that the vasodilatory effects of estradiol (Sobrino et al, 2009) drive these changes in facial coloration (Dixson, 1998; Dubuc et al, 2009), as well as the analogous changes in the color of female hindquarter skin (Dixson, 1998; Dubuc et al, 2009)
Analyses of values on the red color axis revealed significant, positive, within-subject effects of estradiol in both samples of women (Sample 1: t = 2.57, p = .011; Sample 2: t = 3.37, p < .001, Fig. 1). These results indicate that, consistent with our predictions, women’s faces were significantly redder in test sessions where salivary estradiol was relatively high. By contrast with these results for estradiol, these analyses showed no significant effects of either progesterone (Sample 1: t = 1.23, p = .22; Sample 2: t = −0.76, p = .45), or estradiolto-progesterone ratio (Sample 1: t = −0.05, p = .96; Sample 2: t = −0.65, p = .52)
Positive, within-subject effects of estradiol on facial redness were in two independent samples of women
Summary
Facial coloration appears to function as an important social cue in many non-human primate species (Setchell and Dixson, 2001; Waitt et al, 2003; Setchell et al, 2006; Dubuc et al, 2009; Higham et al, 2010). Estradiol may increase blood flow to blood vessels close to the surface of the skin, increasing skin redness (Dixson, 1998; Dubuc et al, 2009) While this potential mechanism for changes in female skin color has been widely accepted, there is no direct evidence that changes in female skin color closely track within-subject changes in estradiol (Dubuc et al, 2009). A critical assumption of the assumed proximate mechanism for changes in primate skin coloration during the ovarian cycle remains untested
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