Acute exposure to thirdhand smoke on the skin elevates biomarkers associated with the initiation of skin diseases, such as 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 study author Shane Sakamaki-Ching in a news release. “Alarmingly, acute dermal exposure to THS mimics the harmful effects of cigarette smoking.”

The study, published in eBioMedicine of is the first to be performed on humans exposed dermally to thirdhand smoke.

The clinical investigation, 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 impregnated with thirdhand smoke and either walked or ran on a treadmill for at least 15 minutes each hour to induce perspiration and increase uptake of thirdhand smoke through the skin. The participants did not know the clothing had thirdhand smoke. 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 thirdhand smoke. Control exposure 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,” says 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.”

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

“There is a general lack of knowledge of human health responses to THS exposure,” says Talbot. “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 thirdhand smoke exposures that the 10 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 says.

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 thirdhand smoke.

PHOTO CAPTION: Skin is the largest organ to contact thirdhand smoke and may thus receive the greatest exposure.

PHOTO CREDIT: Celeste Lum