Many animals use carotenoid-based color signals to indicate their attractiveness, as has previously been discussed here in the context of northern cardinal breeding success. As a refresher, carotenoids are generated by photosynthetic organisms such as plants, bacteria, algae, and fungi, and are responsible for yellowish and reddish coloration--such as cardinals' bright red plumage. Although these hues are typically thought to be "sexy" because they indicate an animal's ability to forage efficiently, they also provide information on an individual's underlying physiology: Because carotenoids help protect tissues against oxidative stress, higher levels of carotenoid coloration may indicate robustness against cardiovascular disease, diabetes, cancers, and other age-related degenerative processes; carotenoids also appear to facilitate immune activity, and may therefore signal the ability to tolerate and/or fight off infection. Given the desirability of those traits in humans, it might not surprise you to find out that we are but one of the many species expressing carotenoid pigmentation. Indeed, recent work by researchers at the University of St. Andrews' Perception Lab has revealed that even small variations in human carotenoid consumption--mainly in the form of fruits and vegetables--can lead to noticeable differences in skin color; further, these differences are associated with how attractive and healthy other people find us to be. These findings were the result of a six-week study of 35 volunteers whose fruit/vegetable intake and skin coloration were recorded at three time points (the beginning of the study, 3 weeks in, and 6 weeks in). Coloration was measured using a spectrophotometer, which shines light onto a patch of interest and then records how much of that is reflected and what colors are present in the reflected light; this yields a metric called CIE L*a*b*, which indicates lightness, redness, and yellowness of the patch of skin (or, in this case, 7 different patches distributed across each participant's body). Read more here.