Association between air pollutant exposure and acne severity in an adolescent cohort in the Netherlands

Acne vulgaris is a prevalent inflammatory skin condition. Increased exposure to air pollutants, such as particulate matter (PM) and nitrogen oxides (NOx), may aggravate acne by damaging the skin barrier and increasing sebum production, leading to more acne-prone skin.1-3 This study examined the association between 3-months prior air pollution exposure and physician-graded acne severity in adolescents in The Netherlands, addressing the lack of population-based research on this topic. This study is embedded in the prospective 'Generation R' study in Rotterdam, The Netherlands,4 including 4422 adolescents around 13 years old with data on air pollution exposure and acne severity. Average exposure concentrations of six pollutants (PM10, PM2.5–10, PM2.5, PM25abs, NOx, and NO2) at participants' home addresses three months before acne evaluation were estimated using land-use regression models.5, 6 Acne severity was graded by physicians using the Global Evaluation of Acne severity score and divided into three ordinal categories: (almost) clear, mild, and moderate/severe.7, 8 We evaluated associations between air pollution exposure and acne severity adjusting for biological sex, ethnicity, maternal education and smoking habits, net household income, and neighbourhood socioeconomic status. Missing values of confounders were imputed using chained equations,9 and inverse probability weighting was performed to mitigate attrition bias. Adjusted odds ratios (AORs) were obtained from single-pollutant multivariable ordinal logistic regressions, evaluating the association between each pollutant and acne severity. AORs display the log-likelihood for an increase in an acne severity category for each unit of increase in air pollutant exposure. The majority of participants (68%) lived around Rotterdam, with the rest dispersed throughout the Netherlands. Half of the adolescents had mild or moderate/severe acne (Table 1). Median pollutant concentrations were 26.1 μg/m3 for NO2, 19.0 μg/m3 for PM10, and 11.0 μg/m3 for PM2.5. Exposure to PM2.5, PM25abs, NO2 or NOx was not associated with acne severity. Higher concentrations of PM10 and PM2.5–10 exposures were associated with lower odds of more severe acne, with AORs of 0.76 (95% CI 0.64; 0.90) per 5 μg/m3 PM2.5–10 increase and 0.73 (0.59; 0.89) per 10 μg/m3 PM10 increase (Table 2). The associations between all air pollutants and acne severity were negative and relatively linear, except for PM10, which showed a negative association at lower concentrations and a positive association at higher concentrations (i.e., > 22.5 µg/m3). Exposure to higher levels of air pollutants were not associated with more severe acne in our study. Instead, we observed unexpected negative associations between PM10 or PM2.5–10 and acne severity, which contrasts with existing literature. We could not find any plausible biological explanations for our results. They are likely due to negative residual confounding, chance, or selection bias. Our median 3-month PM10 concentration of 19 μg/m3 were much lower than the 142 μg/m3 daily levels found in Xi'an, China, where higher pollution was associated with more acne-prone skin.2 The non-linear trend of PM10 in our study indicates a positive association with acne severity at higher concentrations, suggesting results may differ in more polluted areas. Additionally, our study used physician-graded acne severity instead of self-reported outcomes, minimizing misclassification bias and preventing potential overestimation of effect estimates. Our study has several limitations, including potential measurement error in estimating air pollution exposures and the young age of the study population. Although air pollution concentrations at home and school addresses are highly correlated (0.9),10 they may not accurately reflect personal exposure levels. Strengths include the large sample size and the use of validated exposure and outcome assessments. Future research should consider individualized air pollution measurements for more precise exposure assessments, explore other geographical locations, include older adolescent populations for better generalizability, and use longitudinal methods to investigate causal relationships. The general design of the Generation R Study is made possible by financial support from the Erasmus MC, Erasmus University Rotterdam, The Netherlands, Organization for Health Research and Development and the Ministry of Health, Welfare and Sport. This project received funding from the European Union's Horizon 2020 research and innovation programme (LIFECYCLE, grant agreement No 733206, 2016; EUCAN-Connect grant agreement No 824989; ATHLETE, grant agreement No 874583, LongITools, grant agreement 874739). We acknowledge support from the grant CEX2023-0001290-S funded by MCIN/AEI/10.13039/501100011033, support from the Generalitat de Catalunya through the CERCA Program, and from the Instituto de Salud Carlos III (PI20/01695 including FEDER funds). SEDB and LA are employees of L'OREAL. This research is part of an unrestricted research grant by L'Oréal Research and Innovation. All other authors: none. The general design, all research aims and the specific measurements in the Generation R study have been approved by the Medical Ethical Committee of Erasmus MC, University Medical Center Rotterdam. Registration number: MEC 2015-749 NL55105.078.15. All patients in this manuscript have given written informed consent for participation in the study and the use of their de-identified, anonymized, aggregated data and their case details for publication. Data from this study are available upon reasonable request to the director of the Generation R Study ([email protected]), subject to local, national and European rules and regulations.