Air pollution‐induced tanning of human skin*

Abstract

Summary Background Melanism is more frequent in animals living in polluted areas on urban–industrial sites. Given that an increasing number of people are exposed to elevated air pollution levels, it is possible that environmental pollutants affect melanogenesis in human skin. Epidemiological studies have shown that exposure to traffic‐related air pollutants such as diesel exhaust particles (DEP) is associated with more clinical signs of hyperpigmentation. However, mechanistic evidence linking DEP exposure to pigmentation has been elusive. Objectives To develop an ex␣vivo skin model to allow for repetitive topical application of relevant ambient DEP, and to provide proof of concept in humans. Methods We measured skin pigmentation, melanin and pigmentation‐associated gene expression, and evaluated oxidative stress. Results Repetitive exposure of ex␣vivo skin to DEP at nontoxic concentrations increased skin pigmentation. This increase was visible to the naked eye, time dependent, and associated with an increase in melanin content and the transcription of genes involved in de novo melanin synthesis. Similarly, in healthy participants (n = 76), repetitive topical application of DEP at nontoxic concentrations increased skin pigmentation. DEP‐induced pigmentation was mediated by an oxidative stress response. After the application of DEP, epidermal antioxidants were depleted, lipid peroxidation and oxidative DNA damage were enhanced, and in a vehicle‐controlled, double‐blind clinical study DEP‐induced pigmentation was prevented by the topical application of an antioxidant mixture. Conclusions Similar to solar radiation, air pollutants cause skin tanning. As eumelanin is an antioxidant, it is proposed that this response serves to protect human skin against air pollution‐induced oxidative stress.

Structural and Functional Changes and Possible Molecular Mechanisms in Aged Skin

“…Topical exposure of human skin to environmentally relevant concentrations of an internationally established reference standard diesel exhaust mixture increased dark pigmentation of the skin. This tanning effect is due to increased melanogenesis caused by the oxidative stress associated with activation of the p53 signaling pathway [143]. Recently, Li et al [59] showed that indoor air pollution associated with cooking with solid fuels was significantly associated with 5-8% deeper facial wrinkles and folds, and an increased risk of developing fine wrinkles on the dorsum of the hands in Chinese women.…”

Effects of Air Pollution on Cellular Senescence and Skin Aging

“…The composition of atmospheric pollution can also vary depending on the time of day, seasons, human activity, and geographic location [ 8 , 9 ]. Several reports suggest that air pollutant components are direct contributors to the process of aging [ 5 , 11 , 79 , 80 , 81 , 82 ]. Human exposition to air pollution contributes to increased mortality and hospital stays.…”

“…The literature regarding the effects of air pollution on different ethnic skin types is still elusive. The few broad ethnic studies show that exposition of the skin to air pollution mainly induces increased oxidative stress leading to skin pigmentation disorders and wrinkle formation [ 2 , 11 , 72 ]. The majority of the publications are exclusively related to Asian skin [ 87 ] and therefore very biased.…”

“…Given that the interest in the effects caused by exposure to air pollution has risen in the last few years, the number of publications about this topic is constantly increasing. Recent studies show that air pollutants such as particulate matter (PM) can cause skin tanning, skin aging [ 11 , 12 ], and inflammatory skin diseases such as atopic dermatitis (AD), acne, and allergic reactions [ 13 ]. Further investigations are needed to fully understand how skin is affected by the exposure to environmental stressors.…”

Efficacy of a topical serum containing L‐ascorbic acid, neohesperidin, pycnogenol, tocopherol, and hyaluronic acid in relation to skin aging signs

“…Ex vivo human skin was repetitively exposed to 6µg/ml standard reference material SRM 1650b from the National Institute of Standards and Technology (Gaitersburg) in order to induce skin pigmentation. [20][21][22] The serum and its vehicle were applied at 2mg/cm 2 prior to adding DEP. Skin color was assessed by chromametry with a tristimulus colorimeter CR-400 (Konica Minolta).…”