Clinical Review

Guidance for the Clinical Management of Thirdhand Smoke Exposure in the Child Health Care Setting



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 [18]. As thirdhand smoke ages, it becomes more toxic [15]. The aged particles then undergo a process called “off-gassing,” in which gas is continuously re-emitted from these surfaces back into the air [19]. 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 [21].

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 [22]. Environments with potential thirdhand smoke exposure include homes of smokers [23], apartments and homes previously occupied by smokers [24], multiunit housing where smoking is permitted [25], automobiles that have been smoked in [26], hotel rooms where smoking is permitted [27], 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 [28]. 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 [28].

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 [23]. 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 [23]. 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 [29].

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 [9]. 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 [30]. 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 [9].

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 [17]. 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 [17].

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