Thirdhand smoke is residue from tobacco smoke or in other words, the leftover nicotine that remains on surfaces from someone who smoked a cigarette. Thirdhand smoke could cling onto clothes, bags, skin, hair, furniture, walls, carpets, and vehicles.* 
 
The residue can be inhaled, swallowed, or absorbed through the skin, ultimately increasing the risk of lung cancer, heart stroke, liver damage, and diabetes.* These health issues occur because the residue contains toxic cancer-causing compounds that pose a potential health threat to non-smokers.** In particular, children and infants are more vulnerable to thirdhand smoke due to their immature immune systems and tendency to touch and mouth contaminated surfaces.** 
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Thirdhand smoke cannot be eliminated by simply airing out the rooms from an opened window or fan. To remove thirdhand smoke, hard surfaces and fabrics must be cleaned regularly.**
 

*Source: Very Well Health
**Source: Mayo Clinic