Short-Term Air Pollution Exposure Results in Atopic Dermatitis, Itch Increases

Raj P. Fadadu, MS

While wildfires frequently occur in California, they could result in skin exacerbations for atopic dermatitis and itch for adults.

A team, led by Raj P. Fadadu, MS, Department of Dermatology, University of California, San Francisco, examined whether older adults are at a greater risk than younger adults for wildfire pollution-related skin exacerbations.

The Wildfires

In a 2018 analysis, investigators found exposure to smoke from the California Camp Fire, located about 175 miles from San Francisco, resulted in an increase in clinic visits for atopic dermatitis. However, the same was not found for itch in adult patients.

“Because aging affects the barrier function of skin, including alterations in the acidity and hydration of the stratum corneum, transepidermal water loss, and cytokine-mediated inflammation, aging skin may become less resilient to environmental insults, such as air pollution,” the authors wrote.

Examining the Data

In the study, the investigators characterized air pollution using fire status, concentration of particulate matter with diameters 2.5 μm or smaller (PM_2.5), and smoke plume density.

The team collected data on outpatient dermatology visits for atopic dermatitis or itch at an academic medical center in San Francisco between October 1, 2018 and February 10, 2019. They also looked at control data between October 1, 2015 and February 10, 2016 and October 1, 2016 and February 10, 2017.

They aggregated outcome data on a weekly basis, segregated by age and included statistical models for 4 exposure lags and adjusted for temperature, humidity, year, holiday, and overall patient volume at clinics.

Atopic Dermatitis and Itch

Overall, there were 5529 visits for atopic dermatitis and 1319 visits for itch among 3448 unique patients. The mean age of the patient population was 44.6 years and 67.4% of the patients were women (n = 2235).

The results show a 9-fold increase in mean weekly PM_2.5 concentrations between November 8-21, 2018. There was also an adjusted rate of clinic visits for itch in patients aged 65 years or older during a week with a wildfire of 1.6-times (95% CI, 1.1-2.5) the rate of weeks without a wildfire, for a 0-week lag.

The corresponding rate for adults aged 18-64 years was 1.1 (95% CI, 1.1-1.9).

However, a 1-unit increase in mean weekly SPD scores was linked to a 1.4-times (95% CI, 1,1-1.9) increase in clinic visits for itch among adults aged 65 years or old. There was no change in the rate of clinic visits for itch among adults aged 18-64 years (rate ratio, 1.0; 95% CI, 0.8-1.4) for a 0-week lag.

Finally, a 1-unit increase in mean weekly SPD score was linked to a 1.3-times (95% CI, 1.1-1.6) higher rate of clinic visits for atopic dermatitis in the older group and a 1.2-times (95% CI, 1.1-1.3) higher rate for adults aged 18-64 years, with a 0-week lag.

“We found that during short-term exposure to air pollution from a California wildfire, rates of clinic visits for both AD and itch were significantly increased among adults aged 65 years or older, especially at a 0-week lag (during the wildfire), compared with younger adults,” the authors wrote. “In contrast to the statistically nonsignificant increases in visits for itch for all adults aged 18 years or older in a prior study, this study demonstrated statistically significantly increased rates specifically for adults aged 65 years or older. This finding suggests that the skin of older adults has a greater vulnerability to air pollution, with rapid outcomes after short-term exposure to air pollution.”

The study, “Association of Exposure to Wildfire Air Pollution With Exacerbations of Atopic Dermatitis and Itch Among Older Adults,” was published online in JAMA Network Open.