Chen Meng, deputy director of the respiratory department of Nanjing Children's Hospital, said that "third-hand smoke" refers to tobacco residues left on clothing, walls, carpets, curtains, even hair and skin after smokers "swallow clouds and puff fog", which is the most widespread indoor air pollution at present. Nicotine in the residue reacts with nitrite in the air to form a powerful carcinogenic nitrosamine. "Third-hand smoke" is especially harmful to infants, who are more sensitive to "third-hand smoke" and more easily exposed to it in life. Due to the light weight of infants and children, they breathe more air per kilogram of body weight than adults, thus inhaling more pollutants. Moreover, children's immune system is relatively fragile. Inhaling these harmful substances can cause various problems in the respiratory system, nervous system, circulatory system, and even urogenital system. Children's lungs are in the process of development, and their breathing rate is faster, which is more sensitive to "third-hand smoke smoke". Babies under 1 year old mainly crawl and tend to suck their fingers, which makes them easier to contact with "third-hand smoke". An experiment shows that infants and young children can be exposed to 2.2 μ g of nitrosamines every day in the "third-hand smoke" environment, which is about 16 times that of adults. How to avoid the harm of "third-hand smoke"? Experts suggest not smoking indoors or at home in long-term living environments, and not smoking in public places or cars. If someone smokes at home or in the car, timely ventilation, cleaning, or even replacing furniture, clothes, carpets, sofa covers, etc. that may have been contaminated by smoke should be carried out to minimize the harm of residual cigarettes to people. Do not let smokers approach children or pets. If you want to get close to your child, wash your hands and face after smoking. If conditions permit, it's best to wash your hair, take a shower, and change clothes. Try to choose restaurants, training classes, or other indoor places with "no smoking" signs on the walls to reduce the probability of exposure to tobacco. (Lai Xin She)