The perception of “smoking is bad for health” has long been confined to tobacco itself and the smoke it produces by burning. The harm of tobacco to smokers and the health effects of secondhand smoke on non-smokers are well known. However, recently, U.S. experts warned people not to ignore the blowing away of third-hand smoke, especially its harmful effects on children. What is third-hand smoke? After people smoke in a closed room, even if the smoke of secondhand smoke has been dispersed, there is still a significant portion of respirable fine particles stained in the smoker’s clothes, hair and indoor furniture, sofas, etc., these include heavy metals, carcinogens and other harmful substances of tobacco residues is third-hand smoke. In recent years, through the unremitting efforts of our government, the medical profession and the media, people’s awareness of the dangers of tobacco has gradually increased to the level of secondhand smoke. To avoid the hazards of secondhand smoke, many public places have set up special smoking rooms or smoking areas, but can such measures protect the health of all non-smokers? As early as 2004, scientists have begun to study the impact of environmental pollution from tobacco residues on human health. Italian scholars such as Invernizzi published several articles in Tobacco Control, pointing out that the residual respirable particles after smoking can pollute the environment, and that harmful gases (including respirable particles) in the smoker’s lungs will remain for at least 2 minutes. If a smoker enters a smoke-free environment immediately after smoking, it can be harmful to the health of other non-smokers in the environment. After the smoke dissipates, harmful particles will be enriched in the smoking environment, according to Winikoff of Massachusetts General Hospital for Children. Although its degree of environmental pollution is difficult to quantify, it is certain that third-hand smoke pollution will be more serious in a small space like a car. In addition, the smokers themselves (clothes and hair, etc.) are contaminated by third-hand smoke and can “emit” toxic particles that can harm children around them, causing mental retardation and sudden infant death. These findings coincide with the concept put forward by the World Health Organization (WHO) – there is no safe bottom line for tobacco exposure! Children are more vulnerable to the dangers of third-hand smoke Recently, American scholars such as Winickoff found through a survey that people are not aware of the dangers of third-hand smoke. They conducted a telephone survey of 2,000 households to gauge people’s responses to the question, “Does smoking yesterday have any adverse effects on indoor air today and is it harmful to children? Of the 1478 respondents who answered all questions, 273 were smokers. The overall results showed that more than 95.4% of non-smokers and 84.1% of smokers were aware of the health risks of secondhand smoke to children. In contrast, 65.2% of nonsmokers and 43.3% of smokers recognized the harm of thirdhand smoke to children. The amount of awareness of the dangers of thirdhand smoke was significantly associated with whether smoking was banned in the home. In an interview on the Scientific American website, Winickoff mentioned that children are more likely to be exposed to the dangers of thirdhand smoke. Because children have a lower body weight compared to adults, the same levels of toxic substances are more harmful to children. Because of their activities, they are more likely to be exposed to harmful substances that remain in the environment. In addition, children are in a special period of growth and development, their resistance to harmful substances is much lower than that of adults. Therefore, tobacco residues in the environment, including toxic substances such as lead and arsenic, can cause considerable harm to children’s nervous system, respiratory system, circulatory system, etc. Many parents currently believe that smoking while their children are out, and then opening windows to ventilate, will not be harmful to their children’s health. Such a misconception needs to be corrected.