Air pollution from wildfires could worsen eczema and itchy skin, according to the first study to examine the link between wildfire smoke on skin disease.

In the study, published April 21 in JAMA Dermatology, researchers compared dermatology clinic visits for eczema and skin itch with air pollution from the 2018 California Camp Fire, one of the largest and deadliest blazes in the state's history.

Wildfires cause spikes in air pollution, a dangerous mix of noxious gases and fine particulate matter less than 2.5 micrometers in diameter. Known as PM 2.5, these particles penetrate deep into the lungs and can cause respiratory problems, heart disease and cancers. But little is known about how such pollution affects the skin, according to Maria Wei, senior author of the study and a professor of dermatology at the University of California, San Francisco.

"In the Bay Area and along the West Coast in the last five years, we've had an increase in the intensity and frequency of wildfires. That's a trend that's been seen worldwide in all continents except Antarctica," Wei said. "Back in 2018, which is when we started this study, I had a student come to me right during the Camp Fire, which was a fire that took place 175 miles away from San Francisco. It was raining ash outside."

That student, Raj Fadadu, is lead author of the new study. Motivated by the smoky sky, the UCSF and University of California, Berkeley, medical student teamed up with Wei and other colleagues to examine the effects of wildfire-associated air pollution on eczema, also known as atopic dermatitis.

"The skin is the largest organ in the body, and it's really, really well suited for protecting us from the environment and viruses, parasites, bacteria, funguses, irritation and allergens," Wei explained. "The skin is a barrier. But if you have atopic dermatitis, you're born with an impaired barrier. And that makes you more susceptible to anything in the environment and more susceptible to things passing through the skin to the underlying layers." 

The researchers hypothesized that they'd see a rise in atopic dermatitis or general skin-itch visits when air pollution was worse. They looked at patient visits at a dermatology clinic in San Francisco during the Camp Fire, which raged between Nov. 8 and Nov. 25, 2018. During this time, the concentration of PM 2.5 in San Francisco was nine times higher than before or after the fire, according to environmental monitoring data that the team analyzed.

Compared with corresponding dates in years without nearby wildfires, weekly clinic visits for atopic dermatitis were 49% greater for children and 15% greater for adults during the blaze. Similarly, visits for itch increased by 82% for children and 29% for adults at the time of the fire.

"It's not surprising that children might be more affected, because if you're very young, you don't have a mature [skin] barrier, so they might be more susceptible to these effects," Wei explained. 

The researchers also looked at topical and systemic medications prescribed to the patients.

"Systemic steroids are commonly prescribed for atopic dermatitis that's very severe," Wei said. "We saw an almost 50% increase in the number of systemic medications that were prescribed for atopic dermatitis, suggesting that not only is there an effect, but the effect is severe."

The researchers found that 89% of adult patients seen for itch had not previously been diagnosed with eczema, suggesting that wildfire pollution could irritate healthy skin, too.

"You can have itch in the absence of atopic dermatitis, or you can have severe atopic dermatitis and severe itch together. I think that most people think of eczema as rather minor, but don't understand that it can have very severe manifestations as well. It's very, very impactful on people's lives when they have severe atopic dermatitis and/or itch." Wei said.

"Sometimes, people are so itchy they can't sleep, and that affects their global health status," she continued. "Sometimes, they have so much itch that they can't stop scratching, so they break the skin barrier, which leads to infection."

Given that wildfires are predicted to increase in frequency and severity due to climate change, Wei said that this study could form the basis of future policy aimed at educating health care providers and patients on how to protect against the effects of wildfire smoke.

There are several strategies to minimize the harms of air pollution on the skin, according to Wei. Those include applying moisturizer before going out, wearing long sleeves and pants or simply staying indoors. 

"Basically, you want to increase the barrier function of your skin," Wei said.

The researchers acknowledged that a limitation of the study is that they examined just one dermatology clinic during one burning event. Because the composition of PM 2.5 pollution can vary from fire to fire, more research is needed to understand the impacts of wildfire smoke on the skin. 

In future work, the researchers will examine links between wildfire pollution and other skin disorders. 

The study, "Association of wildfire air pollution and health care use for atopic dermatitis and itch," published April 21 in JAMA Dermatology, was authored by Raj P. Fadadu, University of California, San Francisco, University of California, Berkeley, and San Francisco Veterans Affairs Medical Center; Barbara Grimes, University of California, San Francisco; Nicholas P. Jewell, University of California, Berkeley, and London School of Hygiene & Tropical Medicine; Jason Vargo, California Department of Public Health; Albert T. Young and Maria L. Wei, University of California, San Francisco, and San Francisco Veterans Affairs Medical Center; and Katrina Abuabara and John R. Balmes, University of California, San Francisco, and University of California, Berkeley.