Children’s Hands Can Tell Us if They Were Exposed to Thirdhand Smoke

Thirdhand smoke is the toxic chemical residue left behind on surface and in dust when people smoke. When tests that measure nicotine and other tobacco chemicals indicate that children have been exposed to tobacco smoke, researchers have found it difficult to determine if the children’s exposure is from secondhand smoke in the air or thirdhand smoke residue from surfaces or dust. A recent study from San Diego State University suggests that nicotine on the hands of children is one of the most effective ways to measure children’s thirdhand smoke exposure over time and in different environments. In collaboration with colleagues at Cincinnati Children’s Hospital, the researchers wiped the hands of children under 12 years of age and compared the nicotine levels on their hands to urine biomarker tests and parents’ reports of their children’s tobacco smoke exposure. The researchers took all three measures twice for each child in the sample. They did the first test in a medical facility and the second test six weeks later in each child’s home.

The researchers found that overall, the three measures showed good agreement. For example, when one test indicated a high tobacco smoke exposure, the other two did as well. However, the nicotine handwipes were more sensitive and reported higher levels than the urine samples or parent reports. The handwipes likely reported higher levels because they record thirdhand smoke more directly than the other two.

Finding thirdhand smoke on the hands of children suggests that their environments are contaminated with the toxic residue. Thirdhand smoke sticks to surfaces around a home where children live and play, such as carpets, walls, couches, dinnerware, and toys. It also settles in house dust. When children touch this residue with their hands, it sticks to them. If children put their hands in their mouths after touching items with tobacco residue, they can swallow the dangerous chemicals, such as nicotine. Children can also absorb the chemicals through their skin or inhale any that are released into the air.

Children are more susceptible to thirdhand smoke exposure than adults because they tend to spend more time indoors as well as crawl around and put their hands in their mouths more frequently. Their respiratory, skin, and immune systems are still developing, so children breathe faster, have thinner skin, and get sick more frequently than adults. These factors make them more likely to inhale off-gassed thirdhand smoke and absorb thirdhand smoke through touch.

The researchers noticed a few important patterns in their data. In the handwipe tests administered at the hospital (the first wipe test), children who lived in homes where smoking occurs had significantly higher levels of nicotine on their hands than children who live in homes that do not allow smoking and had smoking bans. This was also true in the hand wipe test administered at home (the second test) where children who lived in homes where smoking occurs had almost five times more nicotine on their hands than children who lived in homes with people who did not smoke and had smoking bans. Further, the nicotine levels in the at-home test were significantly higher than the wipe test taken at the hospital.

These findings tell us two important things about thirdhand smoke exposure. First, much of the nicotine on children’s hands comes from their homes. This means that surfaces in homes are a primary source of nicotine exposure for children. Second, homes that have home smoking bans significantly protect their children from nicotine exposure.  

Unlike handwipes, other kinds of exposure tests, such as urine biomarker tests, cannot as easily distinguish between second- and thirdhand smoke. When children are exposed to tobacco smoke, their livers transform the tobacco chemicals into biomarkers that are excreted in urine. This makes it impossible to know if the child inhaled, absorbed, or ingested the chemicals. With the handwipes, though, the nicotine is gathered before the child metabolizes it. In this case, the nicotine must be from thirdhand smoke.

This study concludes that handwipes are an effective – and currently underused – way to measure children’s thirdhand smoke exposure. If handwipes are used more frequently, they may be able help doctors, parents, and researchers understand how children are exposed to tobacco smoke pollutants, allowing them to better protect children’s health from the harms of tobacco smoke.

Click here to read the research study.

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