Air Pollution and Skin Diseases: A Systematic Review of Epidemiological Evidence.

backgroundA growing number of epidemiological studies have suggested a causal link between air pollution and several common skin diseases. However, considerable variation in study design and heterogeneous results make it difficult for clinical dermatologists to judge the true relevance of air pollution as a risk factor for skin diseases.

objectiveWe therefore conducted a systematic review of epidemiological studies to investigate the associations of short- and long-term exposure to ambient air pollutants with atopic dermatitis, psoriasis, urticaria, acne, melanoma skin cancer, non-melanoma skin cancer, and skin aging.

methodsWe systematically searched two comprehensive databases, SCOPUS and PubMed, from 1 January, 1990 to 30 April, 2025 for relevant observational studies. After screening 1393 eligible studies, 77 studies were selected. We defined the level of evidence for causality by assessing the risk of bias in such studies. Ambient air pollutants included particulate matter with an aerodynamic diameter of 10 µm or smaller, particulate matter with an aerodynamic diameter of 2.5 µm or smaller, and gaseous pollutants (nitrogen dioxide, sulfur dioxide, ozone, and carbon monoxide).

resultsWe obtained five major results: (i) the majority of studies strongly advocated the harmful effects of air pollution on the above-mentioned skin diseases, but results across studies were heterogeneous in terms of direction and magnitude. (ii) For all skin diseases, the risk of bias assessment resulted in high risk, which was mainly observed in the domains of confounding, selection bias, and exposure assessment. Consequently, certainty in evidence or causal inference was usually low to very low. (iii) In most studies, high air pollution had a more immediate effect (same day) and lasted up to a week after exposure. (iv) The results on vulnerable subpopulations such as children, older people, or women were inconclusive. (v) Studies were mostly from the upper-middle and higher income countries.

conclusionsDespite numerous epidemiological studies on air pollution and skin diseases, the overall quality of evidence is low. We encourage more longitudinal studies, such as cohort studies or panel studies, to support causality and study change in disease severity over time and improved exposure assessments, and adjustment for critical confounding factors. Importantly, more studies are needed from low- to middle-income countries and on susceptible groups who are most vulnerable to climate change.