What is thirdhand smoke？

A study by the National Laboratory of the U.S. Department of Energy found that “third-hand smoke” refers to tobacco residues left on furniture, cars, clothes, and even hair and skin after smokers “puff up clouds of smoke”, containing more than 250 chemical Substances such as heavy metals, carcinogens and even radioactive substances. The staying time is as long as several months, and it may enter the human body through breathing, hand-mouth contact, skin contact and other channels, causing harm.