Air pollution-induced tanning of human skin.

Melanism is more frequent in animals living in polluted areas at urban-industrial sites. Given that a growing part of the human population is exposed to elevated air pollution levels, we wondered if environmental pollutants might affect melanogenesis in human skin likewise. Epidemiological studies in Caucasians and East Asians indeed showed that exposure to traffic-related air pollutants such as Diesel Exhaust Particles (DEP) is associated with more clinical signs of hyperpigmentation. Mechanistic evidence linking DEP exposure with pigmentation, however, has been develop an ex vivo skin model allowing topical repetitive application of ambient relevant DEP and proof-of-concept in humans.Measurement of skin pigmentation, melanin and pigmentation associated gene expression and evaluation of oxidative stress.Repetitive exposure of ex vivo skin to DEP at non-toxic concentrations increased pigmentation. This increase was visible by the naked eye, time-dependent, associated with an increase in melanin content and transcription of genes involved in melanin de novo synthesis. In healthy subjects (n=76) repetitive topical application of DEP at non-toxic concentrations increased skin pigmentation similarly. DEP-induced pigmentation was mediated by an oxidative stress response, because after DEP application (i) epidermal antioxidants were depleted, (ii) lipid peroxidation and oxidative DNA damage were enhanced, and (iii) in a vehicle-controlled, double-blinded, clinical study DEP-induced pigmentation was prevented by topical application of an antioxidant mixture.Similar to solar radiation, air pollutants cause skin tanning. Since eumelanin is an antioxidant, we propose that this response serves to protect human skin against air pollution-induced oxidative stress.

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Authors: S Grether-Beck, I Felsner, H Brenden, A Marini, T Jaenicke, N Aue, T Welss, I Uthe, Jean Krutmann