Exposure to third hand smoke may trigger skin diseases, study finds

Acute exposure to thirdhand smoke may increase the risk of skin diseases such as contact dermatitis and psoriasis, according to a small study.

Thirdhand smoke (THS) comprises the residual pollutants from tobacco smoke that remain on surfaces and in dust after tobacco has been smoked. It can remain on indoor surfaces indefinitely, causing potentially harmful exposure to both smokers and non-smokers.

Acute exposure of the skin to thirdhand smoke elevates biomarkers associated with the initiation of skin diseases. Biomarkers are natural substances that indicate a biological state, most commonly a disease.

The study, published in eBioMedicine, claims to be the first one to be performed on humans exposed dermally to THS.

"We found that 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," said researcher Shane Sakamaki-Ching from University of California.

The research, which took place at UC San Francisco, involved the participation of 10 healthy, non-smokers who were 22 to 45 years old.

For three hours, each participant wore clothing infused with THS and either walked or ran on a treadmill for at least 15 minutes each hour to induce perspiration and increase uptake of THS through the skin.

"Alarmingly, acute dermal exposure to THS mimics the harmful effects of cigarette smoking. 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," said Sakamaki-Ching.

"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, " said Sakamaki-Ching.

Prue Talbot, a professor of cell biology in whose lab Sakamaki-Ching worked, explained that skin is the largest organ to contact THS and may thus receive the greatest exposure.

"There is a general lack of knowledge of human health responses to THS exposure," said 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 exposures that the ten participants were subjected to were relatively brief and did not cause visible changes in the skin. Nevertheless, the molecular biomarkers in blood that are associated with early-stage activation of contact dermatitis, psoriasis and other skin conditions were elevated.

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

The participants did not know the clothing had THS. Blood and urine samples were then collected from the participants at regular intervals to identify protein changes and markers of oxidative stress induced by the THS.

Control exposure participants wore clean clothing.

Next, the researchers plan to evaluate residues left by electronic cigarettes that can come into contact with human skin. They also plan to evaluate larger populations exposed to longer periods of dermal THS.