Abstract
Skin color diversity is the most variable and noticeable phenotypic trait in humans resulting from constitutive pigmentation variability. This paper will review the characterization of skin pigmentation diversity with a focus on the most recent data on the genetic basis of skin pigmentation, and the various methodologies for skin color assessment. Then, melanocyte activity and amount, type and distribution of melanins, which are the main drivers for skin pigmentation, are described. Paracrine regulators of melanocyte microenvironment are also discussed. Skin response to sun exposure is also highly dependent on color diversity. Thus, sensitivity to solar wavelengths is examined in terms of acute effects such as sunburn/erythema or induced-pigmentation but also long-term consequences such as skin cancers, photoageing and pigmentary disorders. More pronounced sun-sensitivity in lighter or darker skin types depending on the detrimental effects and involved wavelengths is reviewed.
Highlights
Skin color diversity is the most variable and noticeable phenotypic trait in humans resulting from constitutive pigmentation variability
microphthalmia-associated transcription factor (MITF) acts as a master regulator of melanocyte development, function and survival [31] and plays a role in the control of melanogenesis that leads to increased transcription of a range of genes including TYR, tyrosinase-related protein 1 (TRP1) and tyrosinase-related protein 2 (TRP2) involved in the control of the type and amount of melanins produced
More than differences in the nature of clinical signs, photoaging differences can be found regarding the age of onset and the severity of damage that can be explained by the fact that UV and especially UVB rays penetrate in different amounts depending on skin color type and melanin content
Summary
Skin pigmentation is one of the most variable and noticeable phenotypes in humans, but the genetic basis and evolution of this polygenic trait has not yet been fully unraveled. UVR levels are higher than in regions distant to the equator (Figure 1a,b). UV-induced sunburn, skin cancer, immune suppression and photolysis of folate, a metabolite essential for the development of embryonic neural tube and fertility, while light skin would have a biological advantage in regions far from the equator exposed to lower levels of UVR where UVB is needed and corresponds to the effective wavelengths for transformation of 7-dehydrocholesterol to vitamin D3 in the skin, and results in multiple effects on health, ranging from bone metabolism, innate immune response, cell proliferation and differentiation to fertility [2]. (c) Speculative evolutionary tree tree model for human skin skin pigmentation three populations(adapted (adaptedfrom from[3]). As in the section, skin color determined mainly bymainly epidermal melanin pigments, Asdescribed described in the section, skin iscolor is determined by epidermal melanin with a minorwith contribution carotenoidsfrom and (de)oxyhemoglobin from dermal capillaries pigments, a minorfrom contribution carotenoids and (de)oxyhemoglobin from[4].dermal capillaries [4]
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