Carotenoid colour as a cue to health in human skin

Abstract

Carotenoids are red-yellow plant based pigments. When consumed, they contribute to human skin yellowness which in turn is perceived as healthy and attractive looking. In many non-primate species, carotenoids colour sexually selected ornaments, signalling health. This thesis explores the relationship between skin yellowness and aspects of human health to test the hypothesis that carotenoid colouration of skin acts as a cue to health beyond diet.

Chapter 2 presents a demonstration that a modest change in carotenoid intake can lead to a favourable change in appearance. Chapter 3 investigates the relationship between skin yellowness and a number of health related risk factors. Findings show that that psychological stress varies with skin yellowness (independent of fruit and vegetable intake) both between and within participants. Chapter 4 investigates the relationship between prior symptoms of infectious illness (e.g. cold and flus); finding that symptoms experienced during the prior eight weeks are related to skin yellowness between subjects and also within (marginally). More recent symptoms of illness (i.e. the prior week) were not reflected in skin yellowness. The final empirical chapter explores skin colour and plasma carotenoid changes with experimentally induced sickness. Plasma carotenoids were found to reflect baseline skin yellowness and showed a reduction in response to sickness but this reduction was not reflected in skin yellowness. Skin colour did change in a manner consistent with changes in blood perfusion and oxygenation status. A follow-up perceptual study confirmed that this change can reliably inform judgements of health.

Taken together, findings suggest that skin yellowness is related to aspects of health beyond diet (i.e. psychological stress and prior illness) on a timescale of weeks but not days; likely reflecting the time taken for carotenoids to reach the skin. Theoretically, findings support the hypothesis that carotenoid colouration of human skin is a cue to health.