From the Center for Child and Adolescent Health Research and Policy, Division of General Academic Pediatrics, Massachusetts General Hospital for Children, and the Tobacco Research and Treatment Center, Massachusetts General Hospital, Boston, MA.
- Objective: To explain the concept of thirdhand smoke and how it can be used to protect the health of children and improve delivery of tobacco control interventions for parents in the child health care setting.
- Methods: Review of the literature and descriptive report.
- Results: The thirdhand smoke concept has been used in the CEASE intervention to improve the delivery of tobacco control counseling and services to parents. Materials and techniques have been developed for the child health care setting that use the concept of thirdhand smoke. Scientific findings demonstrate that thirdhand smoke exposure is harmful and establishes the need for clinicians to communicate the cessation imperative: the only way to protect non-smoking household members from thirdhand smoke is for all household smokers to quit smoking completely. As the scientific knowledge of thirdhand smoke increases, advocates will likely rely on it to encourage completely smoke-free places.
- Conclusion: Recent scientific studies on thirdhand smoke are impelling further research on the topic, spurring the creation of tobacco control policies to protect people from thridhand smoke and stimulating improvements to the delivery of tobacco control counseling and services to parents in child health care settings.
Key words: thirdhand smoke; smoking; tobacco; indoor air quality; smoking cessation; pediatrics.
While “thirdhand smoke” may be a relatively new term, it is rooted in an old concept—the particulate matter and residue from tobacco smoke left behind after tobacco is burned. In 1953, Dr. Ernest Wynder and his colleagues from the Washington University School of Medicine in St. Louis showed that condensate made from the residue of cigarette smoke causes cancer . This residue left behind by burning cigarettes is now known as thirdhand smoke . Dr. Wynder used acetone to rinse the leftover tobacco smoke residue from a smoking chamber where he had burned cigarettes. He then painted the solution of acetone and thirdhand smoke residue onto the backs of mice. The results of Dr. Wynder’s study demonstrated that exposed mice developed cancerous skin lesions, whereas mice exposed to the acetone alone did not display skin lesions. Dr. Wynder sounded an alarm bell in his manuscript when he wrote, “Such studies, in view of the corollary clinical data relating smoking to various types of cancer, appear urgent. They may result not only in furthering our knowledge of carcinogenesis, but in promoting some practical aspects of cancer prevention .”
Decades of research has been conducted since Dr. Wynder’s discovery to definitively conclude that smoking tobacco and exposure to secondhand tobacco smoke is harmful to human health. It is estimated that 480,000 annual premature deaths in the United States alone are attributable to smoking and exposure to secondhand smoke . The World Health Organization estimates that worldwide tobacco use is responsible for more than 7 million deaths per year, with 890,000 of those deaths caused by secondhand smoke exposure of nonsmokers . Epidemiological evidence of the harm posed by tobacco has spurred the U.S Surgeon General to conclude that there is no risk-free level of exposure to tobacco smoke . Despite the overwhelming evidence implicating tobacco as the cause of an unprecedented amount of disease resulting from the use of a consumer product, only recently has a dedicated research agenda been pursued to study what Dr. Wynder urgently called for back in 1953: further exploration of the health effects of thirdhand tobacco smoke.
The term "thirdhand smoke" was first coined in 2006 by researchers with the Clinical Effort Against Secondhand Smoke Exposure (CEASE) program at Massachusetts General Hospital in Boston , and recent research has begun to shed considerable light on the topic. In 2011, a research consortium of scientists funded by the Tobacco-Related Disease Research Program  in California was set up to conduct pioneering research on the characterization, exposure and health effects of thirdhand tobacco smoke . Research findings from this consortium and other scientists from around the world are quickly expanding and disseminating knowledge on this important topic.
While the research on thirdhand smoke is ongoing, this paper summarizes the current literature most relevant to the pediatric population and outlines clinical and policy recommendations to protect children and families from the harms of exposure to thirdhand smoke.
What Is Thirdhand Smoke and How Is It Different from Secondhand Smoke?
Thirdhand smoke is a result of combusted tobacco, most often from smoking cigarettes, pipes, cigars, or cigarillos. Thirdhand smoke remains on surfaces and in dust for a longtime after smoking happens, reacts with oxidants and other compounds to form secondary pollutants, and is re-emitted as a gas and/or resuspended when particles are disturbed and go back into the air where they can be inhaled . One dramatic example of how thirdhand smoke can remain on surfaces long after secondhand smoke dissipates was discovered on the ornate constellation ceiling in the main concourse of the Grand Central Terminal in New York City. According to Sam Roberts, a correspondent for the New York Times and the author of a book about the historic train station, the dark residue that accumulated on the concourse ceiling over decades and was originally believed to be the result of soot from train engines was primarily residue from tobacco smoke [10–12]. It wasn’t until a restoration in the 1990s when workers scrubbed the tar and nicotine residue from the ceiling could the elaborate design of the zodiac signs and constellations be seen again . A similar process takes place inside homes, where smoke residue accumulates on surfaces such as walls and ceilings after smoking happens. Owners of homes that have been previously smoked in are faced with unanswered questions about how to clean up the toxic substances left behind.
When tobacco is smoked, the particulates contained in secondhand smoke settle on surfaces; this contamination is absorbed deep into materials such as hair, clothes, carpeting, furniture, and wallboard [9,14]. After depositing onto surfaces, the chemicals undergo an aging process, which changes the chemical structure of the smoke pollutants. The nicotine in thirdhand smoke residue reacts with common indoor air pollutants, such as nitrous acid and ozone, to form hazardous substances. When the nicotine present in thirdhand smoke reacts with nitrous acid, it forms carcinogenic tobacco-specific nitrosamines such as NNK and NNN [15–17]. Nicotine also reacts with ozone to form additional harmful ultrafine particles that can embed deep within the lungs when inhaled . As thirdhand smoke ages, it becomes more toxic . The aged particles then undergo a process called “off-gassing,” in which gas is continuously re-emitted from these surfaces back into the air . This process of off-gassing occurs long after cigarettes have been smoked indoors [19,20]. Thirdhand smoke particles can also be inhaled when they get resuspended into the air after contaminated surfaces are disturbed .
Common practices employed by smokers, like smoking in different rooms, using fans to diffuse the smoke, or opening windows, do not prevent the formation and inhalation of thirdhand smoke by people living or visiting these indoor spaces . Environments with potential thirdhand smoke exposure include homes of smokers , apartments and homes previously occupied by smokers , multiunit housing where smoking is permitted , automobiles that have been smoked in , hotel rooms where smoking is permitted , and other indoor places where smoking has occurred.
Research Supports Having Completely Smoke-Free Environments
Recent research has shown that exposure to thirdhand smoke is harmful. These findings, many of which are described below, offer strong support in favor of advocating for environments free of thirdhand smoke contamination for families and children.
Genetic Damage from Thirdhand Smoke Exposure
In 2013, researchers from the Lawrence Berkeley National Laboratory were the first to demonstrate that thirdhand smoke causes significant genetic damage to human cells . Using in vitro assays, the researchers showed that thirdhand smoke is a cause of harm to human DNA in the form of strand breaks and oxidative damage, which leads to mutations that can cause cancer. The researches also specifically tested the effect of NNA, a tobacco-specific nitrosamine that is commonly found in thirdhand smoke but not in secondhand smoke, on human cell cultures and found that it caused significant damage to DNA .
Children Show Elevated Biomarkers of Thirdhand Smoke Exposure in Their Urine and Hair Samples
In 2004, Matt and colleagues described how they collected household dust samples from living rooms and infants’ bedrooms . Their research demonstrated that nicotine accumulated on the living room and infants’ bedroom surfaces of the homes belonging to smokers. Significantly higher amounts of urine cotinine, a biomarker for exposure to nicotine, were detected among infants who lived in homes where smoking happens inside compared to homes where smokers go outside to smoke . As well, a study published in 2017 that measured the presence of hand nicotine on children of smokers who presented to the emergency room for an illness possibly related to tobacco smoke exposure detected hand nicotine on the hands of each child who participated in this pilot study. The researchers found a positive correlation between the amount of nicotine found on children’s hands and the amount of cotinine, a biomarker for nicotine exposure, detected in the children’s saliva .
Children Are Exposed to Higher Ratios of Thirdhand Smoke than Adults
In 2009, researchers discovered that the thirdhand smoke ratio of tobacco-specific nitrosamines to nicotine increases during the aging process . Biomarkers measured in the urine can now be used to estimate the degree to which people have been exposed to secondhand or thirdhand smoke based on the ratio of the thirdhand smoke biomarker NNK and nicotine. Toddlers who live with adults who smoke have higher NNK/nicotine ratios, suggesting that they are exposed to a higher ratio of thirdhand smoke compared to secondhand smoke than adults . Young children are likely exposed to higher ratios of thirdhand smoke as they spend more time on the floor, where thirdhand smoke accumulates. They frequently put their hands and other objects into their mouths. Young children breathe faster than adults, increasing their inhalation exposure and also have thinner skin, making dermal absorption more efficient .
Modeling Excess Cancer Risk
A 2014 United Kingdom study used official sources of toxicological data about chemicals detected in thirdhand smoke–contaminated homes to assess excess cancer risk posed from thirdhand smoke . Using dust samples collected from homes where a smoker lived, they estimate that the median lifetime excess cancer risk from the exposure to all the nitrosamines present in thirdhand smoke is 9.6 additional cancer cases per 100,000 children exposed and could be as high as 1 excess cancer case per 1000 children exposed. The researchers concluded that young children aged 1 to 6 are at an especially increased risk for cancer because of their frequent contact with surfaces contaminated with thirdhand smoke and their ingestion of the particulate matter that settles on surfaces after smoking takes place .