Is thirdhand smoke a risk during pregnancy?

What does the evidence say about thirdhand smoke residue during pregnancy?

1. Thirdhand smoke is the residual matter from tobacco smoke that stays on surfaces and in dust, and exposure to it can occur in households with no active smokers, since it can remain detectable for months after smoking has stopped. 1
2. It is now authoritatively recognized that there is no safe level of exposure to tobacco smoke, in any form, during pregnancy or childhood. 1
3. A toddler mouthing a small piece of fabric contaminated with thirdhand smoke can be exposed to roughly 16 times more nitrosamines per day than an adult who breathes in secondhand smoke, and nicotine residue has been found in smokers' former homes that had been vacant for over 2 months. 2
4. In a mouse study, thirdhand smoke exposure from pregnancy through weaning altered offspring immune function, lowering multiple cytokines and reducing B-cell populations, with effects more pronounced in male offspring. Human research on thirdhand smoke specifically is still limited. 3
5. Secondhand smoke exposure during pregnancy, from any source including a partner or household member who smokes, is linked to a higher chance of pregnancy complications, low birthweight, and birth defects, which is why avoiding smoking anywhere in the home or car matters even if the pregnant person themselves doesn't smoke. 4

Is thirdhand smoke residue safe in each trimester?

• First trimester. There's no trimester-specific human data on thirdhand smoke, but the no-safe-level framing that applies to tobacco smoke generally is most protective to follow during the first trimester, when organs are forming.
• Second trimester. If you're moving into a new home or apartment, keep in mind that nicotine residue has been detected in smokers' former homes that had been vacant for more than 2 months, so a deep clean, or asking about the property's smoking history, is worth doing at any point in pregnancy including the second trimester.
• Third trimester. Toddlers and infants are especially vulnerable to thirdhand smoke because of their low body weight and hand-to-mouth behavior, so the same surfaces, car seats, and furniture you're keeping smoke-free late in pregnancy matter just as much once the baby arrives.