Recognizing the impact of ambient air pollution on skin health

Abstract

Ambient air pollution is a known public health hazard that negatively impacts non-cutaneous organs; however, our knowledge regarding the effects on skin remains limited. Current scientific evidence suggests there are four mechanisms by which ambient air pollutants cause adverse effects on skin health: (i) generation of free radicals, (ii) induction of inflammatory cascade and subsequent impairment of skin barrier, (iii) activation of the aryl hydrocarbon receptor (AhR) and (iv) alterations to skin microflora. In this review, we provide a comprehensive overview on ambient air pollutants and their relevant sources, and highlight current evidence of the effects on skin.

Figure 1

Ambient air pollutants exert deleterious effects on the skin by generating free radicals, inducing cutaneous inflammatory cascades, activating AhR dependent mechanisms, and altering cutaneous microflora. Chronic exposure to ozone results in cumulative oxidative damage to the stratum corneum, ultimately generating free radical species. Furthermore, ozone depletes both enzymatic and non-enzymatic antioxidant reserves in the skin with notable effects on Vitamin C and E levels. In the mitochondria, ozone also depletes ATP and Sirtuin 3 levels, a protein involved in mitochondrial free radical scavenging. In addition to these effects, other pollutants are known to promote a pro-inflammatory environment in the skin resulting in increased levels of IL-1β, IL-6 and IL-8. These mediators activate granulocyte chemotaxis and phagocytosis. Ultimately, these combined processes result in direct and indirect toxicity to the skin. O3, ozone; PM, particulate matter; SO2, sulfur dioxide; CO, carbon monoxide; NOx, nitrogen oxides; VOCs, volatile organic compounds; POPs, persistent organic pollutants; IL - interleukin; PAHs, polycyclic aromatic hydrocarbons; AhR, aryl hydrocarbon receptor; Arnt, AhR nuclear translocator; ATP, adenosine triphosphate; SOD2 - superoxide dismutase 2; NAD+, nicotinamide adenine dinucleotide.