Brief thirdhand smoke exposure can trigger skin diseases, study warns

RIVERSIDE, Calif. — Many people have unfortunately walked into a cloud of secondhand smoke at some point. It’s tough to walk down the block in many cities without catching at least a whiff of tobacco. Thirdhand smoke (THS), meanwhile, is a far more mysterious phenomenon – in large part because it’s so subtle and hard to detect. Now, researchers from the University of California-Riverside say acute exposure to THS can lead to skin disease.

Thirdhand smoke refers to the residual pollutants from tobacco smoke that linger on indoor surfaces like couches or tables, and in dust, long after the cigarette’s been smoked. These particles often remain on surfaces indefinitely, building up more and more over time to the point that THS becomes “embedded” within any number of surfaces including carpeting, clothes, and bedding. While this accumulation is near impossible to notice at first, eventual discoloration and staining is common among walls or countertops habitually exposed to thirdhand smoke.

Study authors explain that this covert accumulation of thirdhand smoke poses a very real health threat to both smokers and non-smokers alike. More specifically, the team at UCR have discovered that acute exposure to THS appears to result in the elevation of biomarkers associated with the development of various skin diseases including contact dermatitis and psoriasis.

“We found exposure of human skin to THS initiates mechanisms of inflammatory skin disease, and elevates urinary biomarkers of oxidative harm, which could lead to other diseases, such as cancer, heart disease, and atherosclerosis,” says Shane Sakamaki-Ching, a former graduate student at UC Riverside who graduated with a doctoral degree in cell, molecular, and developmental biology in March 2022, in a university release. “Alarmingly, acute dermal exposure to THS mimics the harmful effects of cigarette smoking.”

Even brief exposure could damage DNA

This is the first study ever to focus on the impact of THS skin contact in particular. The actual clinical investigation, which took place at UC San Francisco, involved 10 healthy, non-smokers between the ages of 22 and 45. For a period of three hours, each person wore clothing “impregnated” with THS and either walked or ran on a treadmill for a minimum of 15 minutes each hour. This helped promote perspiration and increase uptake of THS through the skin.

Importantly, the participants were not aware they were wearing clothes covered in THS. Next, researchers collected blood and urine samples at regular intervals. This allowed study authors to identify protein changes and markers of oxidative stress induced by the THS. Meanwhile, a control group of participants wore clean clothing.

“We found acute THS exposure caused elevation of urinary biomarkers of oxidative damage to DNA, lipids, and proteins, and these biomarkers remained high after the exposure stopped,” adds Sakamaki-Ching, now a research scientist at Kite Pharma in California, where he leads a stem cell team. “Cigarette smokers show the same elevation in these biomarkers. Our findings can help physicians in diagnosing patients exposed to THS and help develop regulatory policies dealing with remediation of indoor environments contaminated with THS.”

Skin is the most vulnerable ‘organ’ to smoke

Sakamaki-Ching worked out of professor of cell biology Prue Talbot’s lab during this process. She explains the skin is the largest organ to usually make contact with thirdhand smoke, thus receiving the greatest exposure.

“There is a general lack of knowledge of human health responses to THS exposure,” notes Prof. Talbot, the paper’s corresponding author. “If you buy a used car previously owned by a smoker, you are putting yourself at some health risk. If you go to a casino that allows smoking, you are exposing your skin to THS. The same applies to staying in a hotel room that was previously occupied by a smoker.”

The THS exposure that the 10 participants experienced was brief, so it did not cause any visible changes to their skin. However, collected blood molecular biomarkers known to be associated with early-stage activation of contact dermatitis, psoriasis, and other skin conditions were indeed elevated.

“This underscores the idea that dermal exposure to THS could lead to molecular initiation of inflammation-induced skin diseases,” Sakamaki-Ching concludes.

Moving forward, study authors aim to analyze the impact of skin contact with residues left behind by electronic cigarettes, as well as evaluate larger populations exposed to longer periods of dermal THS.

The study is published in the journal EBioMedicine.

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