Could exposure to air pollution be associated with eczema?

People living in areas with higher levels of air pollution within the US are more likely to have eczema, new research in the journal PLOSE ONE has found.

Outdoor air pollution its estimated to cause more than 4 million deaths per year, according to the World Health Organization (WHO). This is mainly due to fine particulate matter – particles smaller than 2.5μm (PM_2.5) in size, which are small enough to travel deep into the airways.

In the new observational study, scientists linked the demographic and electronic health record data of more than 286,000 adults to average annual PM_2.5 concentrations in their post code.

They found that the 12,695 participants (4.4%) diagnosed with eczema lived in areas with significantly higher PM_2.5 concentrations than those without eczema.

Even when controlling for demographics – such as age, sex, race/ethnicity, BMI, income, and smoking status – PM_2.5 concentration was significantly associated with increased risk of having eczema.

“Together with this study, findings from countries across the world support an approximately 2-fold increased risk of eczema with 10 μg/m³ increases in PM_2.5,” the researchers write in the study.

As this research was an observational study, the findings only indicate there is an association between higher levels of air pollution and risk of eczema, not that pollution definitively causes eczema.

However, the researchers point to previous studies that indicate PM_2.5 exposure may influence the risk of eczema through modulating the aryl hydrocarbon receptor (AhR) pathway and causing of oxidative stress, leading to damage to the skin’s epidermal barrier and inflammation.