The Effects of Environmental Pollutants and Exposures on Hair Follicle Pathophysiology

Background: Environmental exposures profoundly impact cutaneous physiology, with hair follicles (HFs) being particularly vulnerable due to their high levels of proliferation and perfusion. HFs are exposed directly to contaminants that are absorbed transcutaneously and exposed indirectly to ingested and inhaled pollutants via the bloodstream. Summary: Some pollutants, such as particulate matter, trigger inflammatory responses and have been associated with alopecia areata. Others, like tobacco smoke and phthalates, exert endocrine effects with unclear ramifications for HF function. Pesticides and heavy metals have both been linked to alopecia areata and acute anagen effluvium, while polyaromatic hydrocarbons – ligands of aryl hydrocarbon receptors – are linked to androgenetic alopecia. Finally, UV exposure, which has increased due to anthropogenic ozone depletion, causes oxidative damage and perifollicular mast cell degranulation. Key Messages: Pollutants have far-reaching consequences for hair pathology, which remain incompletely characterized. The effects of environmental exposures on HFs are an active area of research that deserve further attention.