World No Tobacco Day | We have only heard of second-hand smoke, but where does third-hand smoke lurk?

□ Zhang Wenlou and Deng Furong

May 31, 2024 is the 37th World No Tobacco Day, with the theme of "Protecting Young People from the Harm of Tobacco". Tobacco harm is one of the most serious public health problems in the world. Smoking and secondhand smoke seriously endanger human health. However, there is still a terrible invisible "killer" around us - thirdhand smoke.

What is thirdhand smoke

If someone smokes at home for a long time, the walls, furniture, clothes, etc. will be stained with the smell of tobacco. This is because after smoking, a considerable part of the tobacco smoke particles will adhere to the furniture, sofa, carpet, dust, clothes, and even the surface of hair and skin. These tobacco smoke residues are called third-hand smoke.

The main chemical components of third-hand smoke include nicotine, hydrocyanic acid, lead, arsenic, and many volatile organic compounds. Third-hand smoke attached to the surface of objects will remain for days or even months. Under certain environmental and behavioral conditions (such as tidying clothes), it may be released back into the indoor air and react with chemical pollutants in the air to generate new toxic components of third-hand smoke. For example, nicotine reacts chemically with nitrous acid in the air to generate carcinogens, and household gas is the main source of nitrous acid in indoor air.

The worst-hit areas of third-hand smoke

If first-hand smoke harms oneself and second-hand smoke harms people around, the invisible third-hand smoke is everywhere, harming others and oneself. Smokers' homes and public places such as Internet cafes, restaurants, bars, hotels, and karaoke bars are often the "hardest hit areas" of third-hand smoke. Although public places have designated smoking areas, smoke can easily spread through doors, windows, corridors, and ventilation systems, as well as adhere to smokers' clothing, hair, and skin surfaces, causing non-smoking areas to be contaminated. After smoking or being exposed to second-hand smoke, people will also bring the third-hand smoke attached to their bodies back home, endangering the health of their loved ones. In addition, smokers' family cars and public transportation such as taxis are also heavily polluted areas of third-hand smoke. This is because the carriage is a relatively closed small environment with a high surface-to-space ratio, which is more likely to adsorb and retain smoke residues for a long time.

Thirdhand smoke is harmful to human health

Unlike first-hand smoke and second-hand smoke, which are mainly inhaled through the respiratory tract, third-hand smoke can harm human health through a variety of pathways, including inhalation into the lungs through the respiratory tract, or ingestion through the hand-to-mouth route after contact with the surface of contaminated objects, or even absorption into the body through the skin. Its health hazards are no less than those of first-hand smoke and second-hand smoke. Studies have shown that third-hand smoke can induce respiratory and systemic inflammatory responses, cause metabolic abnormalities in the three major nutrients of carbohydrates, fats and proteins, damage the body's immune function, endanger the reproductive health of women of childbearing age, and affect the growth and development of offspring. In addition, third-hand smoke contains a variety of carcinogenic components, which may increase the risk of diseases such as lung cancer.

Infants and young children are most vulnerable to third-hand smoke

Infants and young children are the most vulnerable group to the harm of third-hand smoke. When crawling or playing, infants and young children like to touch carpets, sofas and other items with their hands. Their skin is easily contaminated with third-hand smoke, and they will ingest smoke residues through habitual eating of their hands. Compared with adults, infants and young children have a faster breathing rate and are more likely to inhale more harmful substances, but their immune systems are not yet fully developed and their ability to metabolize harmful substances is poor. Therefore, infants and young children are more vulnerable to the harm of third-hand smoke. In addition, when we organize clothes and clean the house, third-hand smoke will be suspended in the air, so housewives and hotel service staff are often the main victims of third-hand smoke.

Ventilation does not eliminate third-hand smoke

Unfortunately, some common methods such as ventilation, vacuuming, and air purifiers cannot effectively eliminate third-hand smoke indoors. The most effective measure to prevent third-hand smoke pollution is still to strictly prohibit smoking in homes, cars, and public places. Parents who smoke should avoid smoking at home or in the car. After smoking or being exposed to secondhand smoke, they should not have direct contact with infants and young children, and should bathe and change clothes in time; curtains, sofas, carpets, wallpapers, etc. in smokers' homes that are easy to absorb residual smoke should be cleaned and replaced frequently; non-smokers should try to stay away from places where tobacco smoke exists.

In short, there is no safe bottom line for tobacco exposure. In order to protect you and your loved ones from the harm of third-hand smoke, the most thorough and effective way is to quit smoking! Let us work together to create a smoke-free environment and make our home a real healthy harbor.

(The author Zhang Wenlou is a doctoral student at the School of Public Health of Peking University, and Deng Furong is a professor and doctoral supervisor at the School of Public Health of Peking University)