Thirdhand smoke is a new frontier, and UC's Tobacco-Related Disease Research Program has assembled a consortium of investigators to study the health risks caused by the remnants of cigarette smoke.

The stale smell of cigarette smoke moves many a traveler to request a smoke-free hotel room.  Who wants to smell someone else’s bad habit?  But the lingering odor may be telling us something else — something more troubling.

Research funded by the UC-run Tobacco-Related Disease Research Program (TRDRP) shows that long after smoke has cleared from a room, toxic pollutants from cigarette smoke adhere to bedspreads, carpets, clothing — even furniture, walls, ventilation systems and hallways of hotels that allow smoking. Similar toxicants cling to surfaces in rental cars driven by smokers.

Byproducts of cigarette burning produces potent carcinogens when they combine with common indoor compounds. Many can remain in rooms for months.

 “In the 1950s, we found that smoking could kill you; then research in the '80s and '90s, showed that secondhand smoke is dangerous,” said Georg Matt, a psychology professor of at San Diego State University who focuses on policies to protect nonsmokers.  

“The potential health risks of what we call thirdhand smoke are only now being studied. This is a new frontier.”

Matt is a member of the Cancer Prevention and Control Program at UC San Diego and an investigator in a new thirdhand smoke research effort by the TRDRP.

The TRDRP funded the research consortium in 2011 to bring together experts in a range of fields, from toxicology and chemistry to behavioral and policy research, in order to determine the scope of thirdhand smoke risk and help develop policies to protect people where needed. Consortium researchers presented their findings on thirdhand smoke at the  “Linking Tobacco Control Research and Practice for a Healthier California" conference — held April 10-12 in Sacramento. The conference was sponsored by TRDRP and the state’s Tobacco Control Program.

“We don’t yet know the degree of risk, but we are already finding that indoor smoking leaves a nearly indelible imprint,” Matt said. “We need to find out what risk this pollution poses.”

Risks to infants and toddlers are of particular concern to consortium scientists. Young children crawl on rugs and carpets and often put their hands in their mouths. They have more contact with pollutants that cling to surfaces in the home.

An infant’s developing brain is very susceptible to low levels of toxins, and immature immune systems are particularly vulnerable to persistent pollutants. Researchers suspect that children with respiratory diseases like asthma are likely to be at highest risk.

“This is a newly emerging concern, but one we think is very important to study,” said Anwer Mujeeb, program officer for TRDRP’s thirdhand smoke research effort. “We are leading the way in research to learn how these pollutants form, how long they remain and how they interact. Of course, it’s critical to determine at what concentrations they pose a threat to health.”

TRDRP is funded by California state cigarette taxes and managed by UC. The program launched the thirdhand smoke research consortium with $3.35 million to support a range of investigations.

“We’re very fortunate to have in California scientists who are already making an impact in tobacco research,” said Mujeeb. The research goes hand in hand with efforts to reduce the number of people who take up smoking in the first place.”

Matt and his colleagues in the THS consortium have shown that about 90 percent of nicotine from cigarette smoke remains on indoor surfaces long after the butt is in the ashtray. Their new research shows how much nicotine nonsmokers pick up on their hands from furniture and bedding in hotel rooms where cigarettes have been smoked. Cotinine, a byproduct of nicotine metabolism, shows up in the urine of these nonsmokers after a single night in the hotel room.  

"Secondhand smoke is a mixture of more than 4,000 compounds, including some 50 carcinogens, plus irritants and teratogens (substances that can cause developmental or birth defects). But the potential dangers don’t end with direct exposure to smoke,” Matt said.

In effect, the smoke never really clears.

Consortium research brings together scientists and policy scholars at UC campuses, the Lawrence Berkeley National Laboratory (LBNL) and other sites in and out of the state. Experts vet research proposals, and studies are selected to answer the many unknowns in this new field and integrate findings from different areas of expertise.

Hugo Destaillats and colleagues at LBNL, UCSF and Portland State University have recently found that in just three hours, cigarette smoke and a common indoor home compound known as nitrous acid combine to form a carcinogen at levels 10 times higher than normal. Unvented gas appliances and car engines commonly emit nitrous acid. (See video at top of this page for more about research at LBNL and UCSF.)

The carcinogen formed by the smoke residue and nitrous acid may persist on surfaces in the home long after the cigarette is extinguished, exposing residents any time they are home, Destaillats said.

“Smoking a cigarette can last maybe 10 minutes,” he said. “But the pollutants remain for hours.”

Destaillats is a staff scientist in the Indoor Environment Group of the Environmental Energy Technologies division at Lawrence Berkeley National Laboratories (LBNL) and a professor at Arizona State University. The new research has been published in the Proceedings of the National Academy of Sciences.

“Tackling thirdhand smoke is tough because it’s pushing the technological sensitivity of measurements of pollutants,” said UCSF scientist Neal Benowitz, an authority on nicotine metabolism and principal investigator of the TRDRP thirdhand smoke consortium.

The only way to make solid ressarch progress, he said, is to look at it from many angles: developing biomarkers to measure levels of pollutants, assessing their persistence in the indoor environment and determining how much they are absorbed by the body.

"The effort requires many skills, like environmental chemistry, toxicology, pharmacology and the ability to track and measure the pollutants over time,” said Benowitz, who is vice chair of the UCSF’s Department of Biopharmaceutical Sciences and co-leader of the Center for Tobacco Control Research and Education at UCSF. He is also the leader of the Tobacco Control Program of the UCSF Comprehensive Cancer Center.

“I think the state of California is very forward thinking to try to pursue this question. If anyone has the expertise to make real progress, it’s this talented, multi-discipline research group,” Benowitz said.

The thirdhand smoke trail may well lead to changes in attitudes about smoking and to decisions to give up the habit or not ever start it,  Matt said.

“Afterall, there would be no third or secondhand smoke without ‘firsthand’ smoking,” he said.

One positive sign he’s found is an uptick in the number of people demanding smoke-free used cars, rental cars, apartments and hotel rooms.  

A 2008 study found that used nonsmoker cars were offered for sale at a considerably higher price than their published value and above comparable smoker cars.

“These findings suggest that community preferences are affecting the value of smoke-free cars,” Matt said. “That’s how norms change. And as we close more research and policy loopholes, we’ll have more ammunition to cut down smoking and save lives.”