Temperature, Humidity May Enhance Relationship Between Air Pollution and Atopic Dermatitis

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Study findings suggest that temperature, relative humidity, and air pollution are significantly associated with outpatient visits for atopic dermatitis.

Certain meteorologic factors may modify the effects of air pollution on atopic dermatitis (AD) prevalence, study data published in the Journal of the European Academy of Dermatology and Venereology suggests.

Outpatient visit data for 2013 through 2017 were extracted from the dermatology department at General Hospital of Air Force of People’s Liberation Army in Beijing, China. All outpatient and emergency hospital visits for incident or repeat AD were included in analyses. Daily records of air pollution data were obtained from the Beijing Municipal Environmental Monitoring Center. Air pollution exposures included particulate matter <2.5 μm in aerodynamic diameter (PM2.5); particulate matter 2.5 to 10 μm in diameter (PM10); sodium dioxide (SO2); and nitrogen dioxide (NO2). Data on daily mean temperature and relative humidity during the same period were also collected.

A bivariate response surface model was constructed to investigate the interactive effect of pollutants and other environmental exposures on AD. Temperature-stratified and relative humidity-stratified parametric analyses were conducted to determine whether the relationship between air pollutants and AD differed across temperature and humidity quartiles. Quartile cutoff points were 3.0° C, 15.3° C, and 24.0° C for temperature and 36.0%, 53.0%, and 70.0% for relative humidity.

Data from 64,987 outpatient visits for AD were captured. The daily mean concentrations of PM2.5, PM10, NO2, and SO2 during the study period were 79.7μg/m3, 110.5μg/m3, 50.8μg/m3, and 16.9μg/m3, respectively. The average daily temperature was 13.7° C; mean relative humidity was 53.0%.

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Interactive effects were observed between air pollutants and meteorologic factors. At high temperatures, air pollutants showed strong positive associations with outpatient visits for AD. This trend was particularly pronounced for NO2 and SO2. At extremely low relative humidity, PM10 and SO2 had strong positive associations with the number of outpatient visits for AD.

On stratification analyses, enhanced positive associations of pollutants with outpatient visits were observed at the highest quartile temperature level. At the highest temperature quartile, 10 μg/m³ increases in PM2.5, PM10, NO2, and SO2 were associated with 0.42% (9,5% CI, 0.16%-0.67%), 0.34% (95% CI, 0.15%-0.54%), 1.11% (95% CI, 0.38%-1.84%) and 1.06% (95% CI, 0.21%-1.93%) increases in outpatient visits for AD (all P <.05). Findings were consistent across patient age and sex subgroups.

As patient data were extracted from a single hospital rather than from several facilities across Beijing, data generalizability may be limited. Even so, these results support existing clinical recommendations to minimize skin exposure to pollutants, particularly on hot days. “This study provides further evidence that effects of air pollutants on AD can be modified by meteorological factors, with significant and enhanced effects [on] hot days,” investigators wrote.

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Guo Q, Xiong X, Liang F, Tian L, Liu W, Wang Z, Pan X. The interactive effects between air pollution and meteorological factors on the hospital outpatient visits for atopic dermatitis in Beijing, China: a time-series analysis [published online July 20, 2019]. J Eur Acad Dermatol Venereol. doi:10.1111/jdv.15820