A comprehensive cross-sectional study involving 286,766 participants from the All of Us Research Program found that individuals living in areas with higher concentrations of fine particulate matter faced approximately twice the risk of developing eczema. The study represented one of the largest investigations of air pollution's relationship with eczema in a diverse American adult cohort.

In the study, published in PLOS ONE, investigators found that patients with eczema (n = 12,695) lived in areas with significantly higher particulate matter (PM2.5) concentrations (0.83 x 10 μg/m³) compared with those without eczema (n = 274,127, 0.81 x 10 μg/m³, P < .001).

Key demographic data showed:

• Mean age: 58.44 years (standard deviation [SD] = 16.80) for eczema cases vs 54.85 years (SD = 16.95) for controls
• Female predominance in eczema cases: 65.8% vs 59.8% in controls
• Racial distribution of eczema cases: White (60.5%), Black (17.1%), Hispanic (13.4%), Asian (3.9%)
• Mean BMI: 30.24 (SD = 7.59) for cases vs 29.88 (SD = 7.64) for controls
• Ever-smokers: 38.6% of cases vs 40.0% of controls.

The study revealed three key statistical relationships between PM2.5 and eczema:

• Univariable analysis: odds ratio [OR] = 1.97 (95% confidence interval [CI] = 1.77–2.19, P < .001; AIC 103823)
• Multivariable analysis adjusted for demographics and smoking: OR = 2.58 (95% CI = 2.26–2.95, P < .001; AIC 95421)
• Fully adjusted model including atopic comorbidities: OR = 2.66 (95% CI = 2.32–3.05, P < .001; AIC 89968).

Income distribution among eczema cases showed:

• $100,000/year: 24.9%
• $50,000-$100,000/year: 21.4%
• $25,000-$50,000/year: 15.4%
• < $25,000/year: 21.1%
• Unknown: 17.2%.

The methodology involved linking electronic health records from the All of Us Research Program to air pollution data from the Center for Air, Climate, and Energy Solutions across 788 distinct three-digit zip codes. The investigators utilized HUD-USPS Crosswalk files to match census tract data with zip codes, calculating PM2.5 concentrations through weighted averages based on residential address distributions.

The study population revealed significant differences in atopic comorbidities:

• Allergic rhinitis: 45.4% vs 15.5% (P < .001)
• Asthma: 33.3% vs 15.7% (P < .001)
• Food allergy: 0.9% vs 0.2% (P < .001)
• Eosinophilic esophagitis: 0.7% vs 0.3% (P < .001).

Case identification utilized specific diagnostic codes:

• SNOMED: 43116000
• ICD-10-CM: L20, L30.0, L30.1
• ICD-9-CM: 691, 705.81
• Excluding SNOMED 88996004 and ICD-9-CM 697, 698.3.

The findings aligned with international research:

• Taiwan: OR = 1.63 (95% CI = 1.22–2.16)
• Germany: OR = 2.20 (95% CI = 1.13–4.32)
• Australia: OR = 2.40 (95% CI = 1.20–5.15).

The investigators proposed that PM2.5 may influence eczema development through the aryl hydrocarbon receptor pathway and oxidative stress mechanisms. Polycyclic aromatic hydrocarbons, a major component of PM2.5, can penetrate the stratum corneum and activate pathways leading to barrier dysfunction and inflammation.

These findings had potential clinical implications, particularly when air quality reached the EPA's "moderate" category (12.1–35.4 μg/m³) compared with the agency's "good" category (0–12.0 μg/m³).

Study limitations included three-digit ZIP code geolocation resolution, PM2.5 data availability only through 2015, and lack of clinical detail from visit notes. Additionally, while the All of Us Research Program prioritized diversity, it was not designed to be demographically representative of the entire U.S. population.

The study was partly funded by the National Institute on Aging (Grant No. 2 R01 AG060975). The authors have declared that no competing interests exist.