– Thirdhand smoke – the persistent residue that collects on indoor surfaces where people have smoked – is “clearly” a potentially hazardous exposure, John M. Rogers, PhD, said at the annual meeting of the Teratology Society.

Everyone knows about the hazards of secondhand smoke, which have led to widespread bans on smoking in public spaces. Still, the Centers for Disease Control and Prevention estimates that 58 million nonsmokers in the United States are exposed to secondhand smoke on a regular basis. And where there is secondhand smoke, there is typically exposure to thirdhand smoke as well.

“If you walk into a hotel room you were told is a nonsmoking room and you take one breath and you know it’s not nonsmoking, that’s thirdhand smoke. Thirdhand smoke is all over the place where smokers have been,” explained Dr. Rogers, director of the toxicity assessment division at the Environmental Protection Agency in Research Triangle Park, N.C.

Dr. John M. Rogers, director of the toxicity assessment division at the Environmental Protection Agency in Research Triangle Park, N.C. Bruce Jancin/Frontline Medical News
Dr. John M. Rogers
Tobacco smoke contains thousands of chemicals. Among those known to be harmful developmentally are nicotine, tobacco-specific nitrosamines, lead, cadmium, and various reactive molecules. The odiferous thirdhand smoke residue, composed of tobacco smoke toxins and known cancer-causing agents, adheres to house dust, furniture, carpets, walls, window glass, and other surfaces. It’s difficult to remove. Unlike with secondhand smoke, ventilation won’t do the job.

The main potential health risk is to young children, who ingest thirdhand smoke by the hand-to-mouth route and skin contact.

Thirdhand smoke is a much newer concept than secondhand smoke and has not yet actually been shown to pose a significant health risk. The term “thirdhand smoke” is still unfamiliar to many physicians and the general public. But that is likely to change.

Thirdhand smoke has become an area of intensive research interest, with California leading the way. The Tobacco-Related Disease Research Program, a state agency funded by a tax on the sale of tobacco products, has created a research consortium on thirdhand smoke, with studies underway investigating thirdhand smoke’s precise chemical composition, cytotoxicity, genotoxicity, and true impact on public health (www.trdrp.org).

Concern regarding thirdhand smoke’s potential public health impact ramped up in response to a study in which investigators at the University of York, England, measured levels of various tobacco-specific nitrosamines, N-nitrosamines, and nicotine in house dust samples from the homes of smokers. The researchers estimated that years of early life exposure to these compounds at the levels they detected could result in one excess case of cancer per 1,000 exposed individuals (Environ Int. 2014 Oct;71:139-47).

In addition to his update on thirdhand smoke, Dr. Rogers also touched on other recent tobacco-related developments, including a determination by the Food and Drug Administration that there has been no decline in tobacco use in the last 5 years in adolescents and young adults. While cigarette smoking by young people decreased, this was offset by a large increase in the use of electronic cigarettes and a smaller rise in the use of hookah tobacco. Indeed, e-cigarette use is now about double that of cigarettes among youth.

Also of concern is evidence of a striking socioeconomic disparity in smoking prevalence: Low-education, low-income Americans have far higher tobacco use rates.

“That’s pretty alarming,” he said. “I think a lot of people in this audience probably don’t see a lot of smoking these days, but it’s still around.”

Dr. Rogers drew attention to updated evidence reviews on the reproductive and developmental effects of smoking contained in the U.S. Surgeon General’s voluminous 2014 report on the health consequences of smoking. The report concluded that there is now sufficient evidence to infer a causal relationship between maternal smoking in pregnancy, ectopic pregnancy, and orofacial clefts. The available evidence is “suggestive but not sufficient” to infer causality between maternal smoking in pregnancy and atrial septal defects, clubfoot, gastroschisis, and attention-deficit/hyperactivity disorder and other disruptive behavior disorders.

Dr. Rogers reported having no financial disclosures related to his presentation, which he noted did not necessarily reflect the views and policies of the EPA.