AD Progression Adversely Influenced by Outdoor Air Pollution

Outdoor air pollution has been shown to have both short- and long-term adverse effects among adults living with atopic dermatitis (AD), with implications for AD development, severity, and exacerbation.

Investigators searched Embase and MEDLINE from inception through August 16, 2021, for their review and meta-analysis. The studies included (N = 20) had to be published in English, focus on the potential relationship between adult patients with AD (≥18 years) and outdoor chemical air pollutants (eg, traffic-related air pollution, particulate matter, nitrogen dioxide [NO₂], sulfur dioxide [SO₂], ozone [O₃], carbon monoxide [CO]), and not focus solely on occupational or indoor pollution exposure and tobacco smoking.

Their findings were published in Asian Pacific Journal of Allergy and Immunology, and they evaluated outcomes over both the short (within days) and long (months to years) term.

“The human skin is in direct contact with a variety of environmental factors, such as humidity, allergens, chemical substances, etc, which play an essential role in the pathogenesis of AD. However, few studies have been published on the influence of air pollution on adult AD,” the authors wrote. “We hypothesized that outdoor air pollutants adversely affect AD in adults.”

For long-term impact on AD among an adult patient population, an overall 40% higher risk of developing prevalent AD was associated with exposure to traffic-related air pollution (odds ratio [OR], 1.40; 95% CI, 1.24-1.58), as was a 67% higher risk following exposure to particulate matter smaller than 2.5 mcm (PM_2.5, per 10 mcg/m³ in diameter) (OR, 1.60; 95% CI, 1.26-2.21). In addition, higher risks were seen for incident AD with exposure to both PM_2.5 and NO₂, at 130% (OR, 2.30; 95% CI, 1.25-4.25) and 30% (OR, 1.30; 95% CI, 1.04-1.61), respectively.

Increases of 3.0% (OR, 1.03; 95% CI, 0.3-4.2), 2.7% (OR, 1.27; 95% CI, 0.7-4.7), and 3.0% (OR, 1.03; 95% CI, 1.2-4.7) were also see for AD symptom risk following exposure to a concentration increase of 10 mcm/m³ in particulate matter that was smaller than 10 mcm in diameter (PM₁₀), in NO₂, and in O₃, respectively.

“Furthermore, exposures to these pollutants were more predictive of disease severity than weather factors,” the authors wrote.

For short-term effects, data on AD exacerbations requiring outpatient and/or emergency department visits were analyzed. Using a single lag model, at lag day 0 only SO₂ had a higher associated risk, at 2.9% (OR, 1.029; 95% CI, 1.3-4.7)—although short-erm effects overall often emerged the same day as exposure. Further, a potential link was found between SO₂ exposure and higher AD exacerbation risks ranging from 2.3% to 3.7% per 10 mcg/m³ increment, and although significant associations were seen between O₃ and AD exacerbations risks at lag days 4 and 7, the effects of exposure to PM₁₀, SO₂, and NO₂ attenuated with longer lag time.

Among the adults accounted for in this study, potential effect modifiers of air pollution’s influence against AD were older age, male sex, higher temperatures, and higher socioeconomic status.

With the study authors noting the significant role an impaired skin barrier can play in allowing allergens, microbes, and irritants to penetrate, they note the potential for outdoor air pollution to disrupt this barrier and promote a pro-inflammatory response that includes increases in immunoglobulin E production and reactive oxygen species production, as well as activation of keratinocytes, fibroblasts, and mast cells.

They also encourage further study to counteract these effects, notably in how reducing exposure to these harmful pollutants can have a positive impact on adult patients with AD.

“Outdoor air pollutants exert both short-term and long-term adverse effects on adult AD, contributing to its development, severity, and exacerbation,” the authors concluded. “The influence of air pollution should be considered in the management of adult AD.”

Reference

Hsiao YY, Chen YH, Hung WT, Tang KT. The relationship between outdoor air pollutants and atopic dermatitis of adults: a systematic review and meta-analysis. Asian Pac J Allergy Immunol. 2022;40(4):295-307. doi:10.12932/AP-060922-1448