Thirdhand Smoke: Your Skin Absorbs Nicotine from Air and Clothing

(Inside Science) -- Even if you’re not a cigarette smoker, chances are that at some point in your life, you’ve come home from a night out smelling like an ashtray. The odor may not bother you, but it’s still a good idea to take a shower, or at least change into clean clothes, according to new research.

Nicotine from the air penetrates the skin and enters the bloodstream, and leaving it on your clothes or skin after exposure can be similar to inhaling secondhand cigarette smoke, according to a study published in November in the journal Indoor Air . But wearing clean clothes or taking a shower after encountering nicotine-filled air can help reduce the level of exposure.

“We are all familiar with the situation in which we walk into, say, a hotel room, or even people’s houses -- you can smell that people have been smoking there,” said Hugo Destaillats, a chemist at Lawrence Berkeley National Laboratory in California, who was not involved with this study. You smell it because compounds from the smoke, including nicotine, continue to linger in the air and on surfaces, he said.

We know that nicotine can enter the bloodstream after concentrated and direct contact with the skin, such as the skin patches used to help smokers stop using cigarettes. But last year, scientists from Denmark, Germany and the U.S. published a pilot study demonstrating that skin also absorbs nicotine from cigarette smoke in the air, and at a level comparable to inhalation.

This was surprising because scientists thought that the skin was “a pretty good barrier for compounds [like nicotine] that are in our everyday environment,” said lead author Gabriel Bekö, an assistant professor at Technical University of Denmark, located in Kongens Lyngby.

Those results motivated the scientists to run the experiment again on a larger scale. The researchers released nicotine into an experimental chamber where they could control ventilation and temperature. Inside, nicotine levels reached higher than most places where smoking occurs, but comparable to levels reported for bars and clubs in the U.K. and Germany.

Six test subjects -- all men who were researchers involved with the study -- spent five hours at a time in the chamber while wearing a breathing hood that supplied clean air. Participants 1 through 4 wore only shorts while in the chamber, and didn’t shower until the next morning. Participants 3 and 4 repeated the experiment the following week, but this time showered immediately after exiting the chamber.

Participants 5 and 6 were fully clothed: pants, a long-sleeved shirt, socks and gloves. The first week, they sat in the chamber while wearing clean clothes. A week later, they sat in the chamber wearing clean pants, but the rest of their garments had previously been exposed to nicotine and not washed.

The researchers collected urine samples from all participants at multiple times throughout the experiments and measured the levels of nicotine plus two other chemicals the body produces from nicotine.

Similar to the pilot study results, the men who were wearing only shorts absorbed nicotine from the air in substantial amounts, equivalent to levels from inhalation exposure. Showering immediately after exposure significantly reduced the amount of nicotine in one of the men, but resulted in only a marginal decrease for the other. There was a large age difference between those two participants that might explain the different outcomes, but Bekö cautioned that this is just speculation.

The men who wore clean clothes while in the chamber had the lowest levels of nicotine, although still well above the level before they entered the chamber. But when they wore dirty clothes, previously exposed to nicotine, their nicotine uptake skyrocketed. This indicates that “clothing can be protective if it’s clean, but on the contrary can act as a very direct source because of the contact with the skin if it’s contaminated,” said Destaillats.

For all participants, nicotine and related chemicals were still seen in substantial amounts in urine samples taken three and a half days after exposure. This is longer than it typically takes the body to eliminate inhaled nicotine, said Bekö. This likely means the body handles nicotine that enters from the skin differently than nicotine that enters via the lungs.

“We always think about secondhand exposure that is smoke in your face,” noted Destaillats. But, he said, this study highlights the fact that just being in an environment that was previously contaminated some time ago can result in exposure to thirdhand smoke, which could be significant.

Bekö believes research on uptake through the skin needs more attention. “We believe this is a very important area to understand,” he said. “What are the potential effects, and what can be done about it?”