Can skin color communicate the health status of an individual and change according to diet?
Numerous animal species, such as some species of birds, are known to select mates in part based on the intensity of colors they display. Studies also show that the display and change in colors can in part be linked to diet and health status.
Now, how about humans? Are we also susceptible to health signals passed on through other people’s skin, or even our own?
Of course, differences in human skin melanin pigmentation across geographic regions of the world of origin present some of the most noticeable differences in skin color, all while communicating characteristics such as resistance to sunburn and decreased skin cancer risk. However, other colors may convey information we are not completely aware of yet.
Most smartwatches use technology to measure heart rate by interpreting subtle skin color changes caused by blood flow reflected through the surface of the skin. While the human eye can’t pick up on that level of detail, we know that other changes are visible. For example, blushing conveys embarrassment, and people may notice someone’s “skin glow” without realizing it.
Skin glow and healthy habits
Have you ever eaten lots of mango, carrots, or any fruits and vegetables, and noticed yourself get slightly more attractive? It’s likely too subtle for you to tell as it happens slowly, but others might!
This particular glow comes from yellow-orange plant pigments that are obtained from most fruits and vegetables. These plant pigments are called carotenoids and they have antioxidant properties like vitamin C.
This got a group of researchers from the University of St Andrews thinking: if this glow is associated with intake of fruits and vegetable and their carotenoids, which are both associated with a decreased disease risk, could the glow communicate more information concerning a person’s health?
Researchers demonstrated that better fitness and lower percent body fat were predictors of the carotenoid-associated skin glow, independent of each other and fruit and vegetable intake, in a cross-sectional study of 134 participants from the United Kingdom
The researchers also went on to demonstrate that increases in fitness and decreases in body fat, after 8 weeks of returning to sports practices, were independently associated with increases in skin glow of 59 university athletes.
Even self-reported sleep and stress predicted skin glow!
Basically, more sleep and less stress could equal increased glow.
Pushing the boundaries on the meaning of skin color
The researchers measured fitness by estimating how efficiently people use oxygen during exercise with a smartwatch (yes, smartwatches can do that too now).
Body fat percentage was estimated by using an electric scale that shot a weak electric current through the body. The more resistance the current has as it goes from one side to the other, the more water there is in the body, which in turn generally means more muscle. Since fat cannot hold water, this method allows to estimate fat-free body mass. Then, with body weight measurement using a scale, researchers were able to calculate an estimated body fat percentage.
The researchers even went on to simulate the glow associated with fitness by creating a color filter for photos. They then asked 21 participants to apply more or less of the color filter onto photos of faces to make them look healthier.
The participants ended up applying levels of color that were associated with better fitness.
This study suggests that although skin color changes are very subtle, we may unknowingly be able to detect signals that communicate healthiness.
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* Ce texte a été produit dans le cadre du concours de vulgarisation scientifique organisé par le comité étudiant de l’Institut sur la nutrition et les aliments fonctionnels de l’Université Laval.
Ressources
Référence de l’article vulgarisé : Perrett, D. I., Talamas, S. N., Cairns, P. & Henderson, A. J. Skin Color Cues to Human Health: Carotenoids, Aerobic Fitness, and Body Fat. Front. Psychol. 11, (2020).