RIVERSIDE, Calif. — Many people have unfortunately fallen into a cloud of second-hand smoke at some point. It’s hard to walk the block in many cities without grabbing at least one puff of tobacco. Third-hand smoke (THS), on the other hand, is a much more mysterious phenomenon, largely because it is so subtle and difficult to detect. Now, researchers from the University of California, Riverside claim that acute exposure to HRT can lead to skin diseases.
Third-hand smoke refers to residual pollutants from tobacco smoke that linger on indoor surfaces like sofas or tables, and in dust, long after the cigarette has been smoked. These particles often stay on surfaces indefinitely, accumulating more and more over time to the point that the THS becomes “embedded” in a number of surfaces, including carpeting, clothing, and bedding. Although this buildup is nearly impossible to notice at first, discoloration and eventual staining are common among walls or countertops that are usually exposed to thirdhand smoke.
The study authors explain that this covert accumulation of third-hand smoke poses a very real threat to the health of smokers and non-smokers alike. Specifically, the UCR team found that acute exposure to HRT appears to lead to an elevation of biomarkers associated with the development of various skin diseases, including contact dermatitis and psoriasis.
“We found that exposure of human skin to THS initiates inflammatory skin disease mechanisms and elevates urinary biomarkers of oxidative damage, which could lead to other diseases, such as cancer, heart disease and atherosclerosis,” Shane Sakamaki-Ching, a former graduate student at UC Riverside who earned a doctorate in cell, molecular, and developmental biology in March 2022, says in an academic publication. “Alarmingly, acute dermal exposure to HRT mimics the harmful effects of smoking.”
Even brief exposure could damage DNA
This is the first study to focus on the impact of HRT 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 three-hour period, each person wore clothing “soaked” with THS and walked or ran on a treadmill for at least 15 minutes per hour. This helped promote sweating and increased absorption of THS through the skin.
Importantly, the participants were unaware that they were wearing HRT-covered clothing. Then the researchers took blood and urine samples at regular intervals. This allowed the study authors to identify protein changes and markers of HRT-induced oxidative stress. Meanwhile, a control group of participants wore clean clothes.
“We found that acute exposure to HRT elicited elevations in urinary biomarkers of oxidative damage to DNA, lipids, and proteins, and these biomarkers remained elevated after exposure ceased,” adds Sakamaki- Ching, now a researcher at Kite Pharma in California, where he leads a stem cell team. “Cigarette smokers show the same elevation of these biomarkers. Our results can help physicians diagnose patients exposed to HRT and develop regulatory policies addressing the remediation of indoor environments contaminated with HRT.
The skin is the “organ” most vulnerable to smoke
Sakamaki-Ching worked in the lab of cell biology professor Prue Talbot during this process. She explains that the skin is the largest organ that typically comes into contact with third-hand smoke, thus receiving the greatest exposure.
“There is a general lack of knowledge about human health responses to HRT exposure,” notes Professor Talbot, the paper’s corresponding author. “If you buy a used car that was previously owned by a smoker, you are putting yourself at some risk to your health. If you go to a casino where smoking is allowed, you are exposing your skin to HRT. The same applies to staying in a hotel room that was previously occupied by a smoker.
The exposure to HRT that the 10 participants experienced was brief and therefore caused no visible changes to their skin. However, collected blood molecular biomarkers known to be associated with the early activation of contact dermatitis, psoriasis and other skin conditions were indeed elevated.
“This underscores the idea that dermal exposure to THS could lead to the molecular initiation of inflammation-induced skin diseases,” Sakamaki-Ching concludes.
Going forward, the study authors aim to analyze the impact of dermal contact with residues left behind by e-cigarettes, as well as to assess larger populations exposed to longer periods of dermal HRT.
The study is published in the journal EBioMedicine.