Pollution and Sun Exposure: A Deleterious Synergy. Mechanisms and Opportunities for Skin Protection

Background: Pollutants are diverse chemical entities, including gases such as ozone and particulate matter PM. PM contains toxic chemicals such as polycyclic aromatic hydrocarbons (PAHs). Some PAHs can induce strong oxidative stress under UVA exposure. Pollution aggravates some skin diseases such as atopy or eczema, but epidemiological data also pointed to a correlation with early occurrence of (photo)-aging markers. Objective: This paper aims at reviewing current literature dealing with dermatological effects of pollution, either on in vitro models or using in vivo approaches (including humans). It particularly focuses on the probable deleterious synergy between pollutants and sunlight. Results: An exhaustive analysis of literature suggests that skin may be impacted by external stress through oxidation of some of its surface components. However, pollutants detected in plasma may also be provided to deep skin by the circulation of the blood. Oxidative stress, inflammation and metabolic impairments are among the most probable mechanisms of pollution- derived dermatological hazards. Moreover these stresses should be amplified by the deleterious synergy between pollution and sunlight. Some experiments from our lab identified few PAHs inducing a huge toxic stress, at nanomolar concentrations, when exposed to long UVA wavelengths. Prevention strategies should thus combine surface protection (long UVA sunscreens, antioxidants) and enhanced skin tissue resistance through stimulation of the natural antioxidation/detoxification pathway Nrf2. Conclusion: In people exposed to highly polluted environments, pollutants and sunlight may synergistically damage skin, requiring a specific protection.