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Updated: May 26, 2026

Pharmacologic Induction of Epidermal Melanin and Protection Against Sunburn in a Humanized Mouse Model
Published on: September 7, 2013
Immediate pigment darkening: its evolutionary roles may include protection against folate photosensitization
Johan Moan1, Kristian Pagh Nielsen, Asta Juzeniene
1Department of Radiation Biology, Institute for Cancer Research, Norwegian Radium Hospital, Oslo University Hospital, Montebello 0310 Oslo, Norway.
Abstract:
The evolution of dark human skin colors in tropical areas is possibly related to photoprotection of folates. However, natural folates absorb mainly UVB radiation, and too little UVB can penetrate down to folates in dermal vessels to cause serious damage. However, endogenous photosensitizers, like riboflavin and uroporphyrin, absorbing UVA and visible light, can cause photosensitization of folates. Immediate pigment darkening (IPD), generated by UVA, has an absorption spectrum covering those of the endogenous photosensitizers. IPD is most prominent for darker skin types, which were typical for populations living under tropical solar fluences. We here propose that the biological role of IPD is protection of folates against photodegradation, which would be of large evolutionary importance for early hominids.
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