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Introduction
Smokers always think that as long as they don't smoke in front of their children, they won't cause harm to their children. However, existing studies suggest that children may be the biggest victims of "third-hand smoke".
Written by | Chu Xu (Department of Respiratory Medicine, First Affiliated Hospital of Henan University of Science and Technology)
Editor-in-charge | Zhang Han
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Today, the main bad elements of cigarette smoke - the harm of first-hand smoke and second-hand smoke, especially to children, is almost well known. So we often hear the phrase "I never smoke at home" or "I never smoke in front of my kids."
Smokers always think that as long as they don't smoke in front of their children, they won't cause harm to their children. But is this really the case? Today we're going to talk about the "non-mainstream" molecules in smoke exposure -- "third-hand smoke."
What is third-hand smoke? Third-hand smoke is defined as residual tobacco smoke attached to the surface of indoor objects, as well as gases and suspended particles re-released from the surface of contaminated objects to which these third-hand smoke is attached, and also includes new pollutants produced by the reaction of residual smoke compounds on the surface of the object with the compounds in the indoor air after smoking has been stopped [1]. In grounded terms, it is probably the smoke particles that remain on the surface of your skin, clothes and sofas and furniture at home after you smoke, and these compounds will also chemically react with the compounds in the environment to produce more harmful substances.
It can be seen from the definition that third-hand smoke is different from first- and second-hand smoke, and first- and second-hand smoke is often in the air and spit out by smokers through the mouth. First, the biggest "benefit" of second-hand smoke is its avoidability: if you do not have contact with smokers, do not share a closed environment with smokers, you can not contact its smoke hazards.
The biggest problem with third-hand smoke is precisely its strong adhesion, and cigarette particles can be detected on the skin, clothes, hair of smokers, and on the surrounding environmental items such as sofas, cabinets, and floors in their smoking environment. When a smoker is out smoking, once he returns home, the particles on his skin, clothes, and hair follow him home, and then attach to items such as sofas in the home.
From this process, we can see which member of the family is most likely to come into contact with the smoker's clothes and is the most harmful. Therefore, research on third-hand smoke is almost always carried out among housewives and infants and young children. Because of the influence of traditional culture, housewives take on more work such as washing clothes and cleaning the surface of goods, so there are more opportunities to contact the smoke particles attached to them. Another group is infants and young children, who are small in size, have a limited range of motion, like to play on the surface of objects such as the floor and sofas, and like to suck on objects and fingers, which is extremely risky.
A cross-sectional survey led by Jinan University in China included a total of 15682 pregnant women, of whom 7564 (48.2%) were not exposed to tobacco, and the number of pregnant women exposed to primary, second- and third-hand smoke was 89 (0.6%), 2349 (15.0%) and 5680 (36.2%), respectively. These pregnant women were then scored on the EuroQol Visual Simulation Scale, which is primarily used to evaluate the physical and mental health of individuals. It was found that pregnant women without tobacco exposure scored the highest on the scores, while those exposed to first-hand, second-hand and third-hand smoke had significant differences in their scores from those without tobacco exposure. This means that whether it is first-hand, second-hand or third-hand smoke, it will cause damage to the physical and mental health of pregnant women [2].
The biggest victims of third-hand smoke are infants and young children, because this group is easily exposed to large amounts of third-hand smoke during home activities. Pregnant women with smokers in the family have been shown to be more likely to give birth prematurely, and exposure to third-hand smoke can lead to microbiome changes in the neonatal gut microbiota [3]. It has also been reported that third-hand smoke can lead to a significant increase in the α diversity of microbial phylogenetic development in infants and young children, which means that the types and distribution of intestinal microorganisms in these infants are different from those of infants without smoke contact, especially the distribution and number of bacterial species such as Corynebacterium, Bifidobacterium, Staphylococcus, streptococcus, etc., and this change in intestinal microbiome may be involved in the pathogenesis of bronchial asthma, bronchitis, otitis media and many other diseases in childhood [4].
In addition, multiple studies have also found other damage to third-hand smoke.
In mouse experiments, it was found that third-hand smoke exposure can affect the synthesis and metabolism of biochemical substances by the liver, the largest chemical plant in animals, causing biochemical dysfunction in the liver and affecting many metabolic pathways. For example, third-hand smoke can affect the metabolism of glycerophospholipids and glutathione, and glutathione is an important substance for the body to resist oxidative stress damage, and its metabolic abnormalities will lead to a decrease in the body's antioxidant capacity. Third-hand smoke can also lead to lipid accumulation in the liver, a decrease in metabolites involved in choline phosphate synthesis, and choline deficiency in mice, all of which are associated with the onset of non-alcoholic fatty liver disease. That is, third-hand smoke can affect liver function from the molecular level [5].
As we all know, nicotine is the number one killer among the many toxic substances in cigarette smoke, after nicotine enters the human body, its primary metabolite cotinine is mainly present in the blood and excreted through urine. Because of its long half-life, cotinine is often used as a marker to assess smoking or passive smoking.
A cross-sectional study in Barcelona found that the content of cotinine in the saliva of people exposed to third-hand smoke was significantly higher than that of those exposed to cigarette smoke, and there was no statistically significant difference in the content of cotinine in the saliva of people exposed to second-hand smoke and third-hand smoke. The results of this study suggest that exposure to third-hand smoke can cause nicotine to enter the human body and cause harm comparable to that of secondhand smoke [6].
However, the problem of third-hand smoke has never been taken seriously. Its harm is not yet widely understood by the public, and even most medical professionals are not yet aware of the harm of third-hand smoke. And the above research suggests that children may be the biggest victims of third-hand smoke. In traditional Chinese culture, children are the core of the whole family. For the sake of the physical and mental health of the next generation, if you have the habit of smoking, it is recommended that you quit smoking from now on.
"Never smoke at home" does not prevent third-hand smoke from harming the health of your family; only "I do not smoke" can make you feel at ease to enjoy the good time with your loved ones.
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