Third-hand smoke is contamination by tobacco smoke that lingers following the extinguishing of a cigarette, cigar, or other combustible tobacco product. [1] First-hand smoke refers to what is inhaled into the smoker's own lungs, while second-hand smoke is a mixture of exhaled smoke and other substances leaving the smoldering end of the cigarette that enters the atmosphere and can be inhaled by others. Third-hand smoke or "THS" is a neologism coined by a research team from the Dana–Farber/Harvard Cancer Center, where "third-hand" is a reference to the smoking residue on surfaces after "second-hand smoke" has cleared out.
Humans can be exposed to THS through inhalation, skin contact, or ingestion. Many common surfaces can accumulate THS compounds, including furnishings, walls and flooring, and clothes. THS is thought to potentially cause the greatest harm to infants and young children because younger children are more likely to put their hands in their mouths or be cuddled up to a smoker with toxins on their skin and clothes. [2] Infants also crawl on the floor and eat from their hands without washing them first, ingesting the toxins into their still developing systems. [3]
According to a study conducted by Northrup, 22% of infants and children are exposed to SHS/THS in their homes each year, comprising a major proportion of the 126 million nonsmokers exposed to harmful tobacco products annually. [4]
Though research is limited, there are many harmful health effects that have been linked to THS exposure. THS has the potential to impair wound healing by altering the body’s natural anti-inflammatory response, remodel respiratory structure due to increased collagen deposits in airways, and cause permanent damage to DNA. Other health effects include asthma, increased cough morbidity, and other respiratory conditions. [5] If pregnant mothers are exposed to THS, it can slow fetal lung development in the third trimester. In children, THS exposure has also been linked to sudden infant death syndrome (SIDS) as a potential cause factor, [6] and has also been linked to cognitive and memory deficits in growing children. [7] Whether or not these largely theoretical relationships are actually causal in humans at realistic exposure levels remains to be seen. [8]
Third-hand smoke has also been tested in various cell assays. THS exposure by cells have been shown to lead to the observation of DNA strand breaks, inhibition of proliferation, and cell death. Acrolein has shown to be a particularly potent third-hand smoke gas. [9]
A study led by Ashley Merianos, a tobacco researcher at the University of Cincinnati, revealed that in homes where children live, surfaces were contaminated with nicotine and the tobacco-specific carcinogen NNK. This was observed even in homes with voluntary indoor smoking bans, highlighting the persistent nature of THS pollutants. The study revealed higher levels of NNK and nicotine in lower-income households and homes who do not ban indoor smoking. [10]
Third-hand smoke and its components have been detected in a variety of indoor environments. The possibility of nitrosamine formation on vehicular surfaces was identified via the spraying of "high but reasonable" levels of nitrous acid (about 4–12 times the levels typically found in homes) onto cellulose substrates and wiping surfaces in a vehicle that had experienced heavy smoking. [2] Similar results were found when cellulose substrates were kept (without wiping) in the same vehicle for three days when smoking occurred. [2] Additionally, the persistence of various third-hand smoke components was quantified on wool, cotton, and polyester fibers [11] with THS the most persistent on wool and least persistent on polyester. Washing clothing without detergent was found to remove some THS, though a substantial amount remained after standard laundering. [11]
Because of the growing resolving power and improved detection limits of analytical instruments, studies have been able to demonstrate the transport of THS into other spaces via various media. For instance, third-hand smoke signatures have been detected in particles, which can effectively transport such compounds between indoor and outdoor air. [12] [13] Additionally, both gas-phase and aerosol-phase compounds linked to third-hand smoke were detected and quantified in a non-smoking movie theater, possibly via moviegoers' clothes and breath. [14]
Environmental tobacco smoke can oxidize with environmental nitrous acid to create carcinogenic tobacco-specific nitrosamines (TSNAs). [2] One TSNA, called 4-(methylnitrosamino)-1-(3-pyridinyl)-1-butanone (also known as nicotine-derived nitrosamine ketone, or NNK), is a potent lung-specific carcinogen ubiquitous in tobacco smoke and smokers' homes, and has been detected on clothing fibers, dust, and in the air. [11] [15] Nitrosamines, along with other tobacco smoke chemicals that deposited on surfaces or compounds that formed as a result of surface-phase reactions, can be a major source of toxicity, especially for infants. Infants can be particularly adversely affected given their frequent close proximity to household surfaces and their propensity to ingest third-hand smoke residue from surfaces and dust. [2]
It is important to acknowledge the biomarkers of third-hand smoke because they indicate the severity and presence of disease. In a recent study involving mice, biomarkers of THS were discovered after four weeks of initial exposure at equivalent levels to those found in homes of smokers. Researchers used a system that mimicked that of the exposure to humans and sought out biomarkers found in serum, liver, and brain tissues in the mice. The mice were then exposed to THS at varying months and at as early as one month, they began to show signs of increased circulating inflammatory cytokines, tumor necrosis factor, granulocyte macrophage colony stimulating factor, and an increase in the stress hormone epinephrine. [16] Damage from THS exposure continued after two, four, and six months. Such damages included oxidative stress and molecular damage. Some of the mice also became hyperglycemic and hyperinsulinimic, which could mean that insulin resistance could be a consequence of long-term exposure. [16] This study implies that increased exposure time to THS can have dramatic effects. Additional studies with human subjects are still needed to fully understand the implications of THS.
Third-hand smoke is a relatively newly postulated concept, and public awareness of it is lower than that of second-hand smoke. A 2013 study with six focus groups in metro and rural Georgia (USA) asked participants whether they had heard of THS, most of the participants had not heard about it and did not know what third-hand smoke was. [17] Research on THS is growing, but does not compare to the 40 years of research on the effects of second-hand smoke. Yet, it is estimated that 5%-60% of second-hand smoke-related harm may actually be attributable to third-hand smoke exposure. [4] THS poses such a risk because its exposure can linger much longer than second-hand smoke. Third-hand smoke-contaminated surfaces like carpet, walls, and car interiors are also especially hard to clean whereas second-hand smoke can be removed with ventilation. [4]
Smoking rates in the United States have fallen considerably from a high of 42.4% in 1965 to around 17.8% in 2016. But the downward trend is slowing and it is estimated that 23% to 42% of adults in America with low education or living in poverty still smoke. This exposes millions of nonsmokers, many of which are children. [4]
Awareness campaigns for THS are steadily growing in number and primarily focus on the health risks for young children. A 2014 study published in Pediatrics demonstrated that parents are more likely to attempt to quit smoking if they become convinced that third-hand smoke is harmful to children and are more likely to have smoke-free home and car policies if they are aware of the dangers of third-hand smoke. It was recommended for parents to safeguard their children by ensuring they have a smoke-free zone. One such way recommended for smokers to protect family, friends and others is by smoking outside and showering and changing clothes before coming into contact with others. [18] However, research has shown that parents who are heavy smokers (> 10 cigarettes per day) are less likely to believe that third-hand smoke is harmful to children. [19] Third-hand smoke is one of the issues promoting indoor smoking bans, especially supported by performers such as musicians, who are forced to bring third-hand smoke contamination into their homes through contaminated instruments and cases.
Nicotine is a naturally produced alkaloid in the nightshade family of plants and is widely used recreationally as a stimulant and anxiolytic. As a pharmaceutical drug, it is used for smoking cessation to relieve withdrawal symptoms. Nicotine acts as a receptor agonist at most nicotinic acetylcholine receptors (nAChRs), except at two nicotinic receptor subunits where it acts as a receptor antagonist.
A cigarette is a narrow cylinder containing a combustible material, typically tobacco, that is rolled into thin paper for smoking. The cigarette is ignited at one end, causing it to smolder; the resulting smoke is orally inhaled via the opposite end. Cigarette smoking is the most common method of tobacco consumption. The term cigarette, as commonly used, refers to a tobacco cigarette, but the word is sometimes used to refer to other substances, such as a cannabis cigarette or a herbal cigarette. A cigarette is distinguished from a cigar by its usually smaller size, use of processed leaf, different smoking method, and paper wrapping, which is typically white.
Tobacco smoke is a sooty aerosol produced by the incomplete combustion of tobacco during the smoking of cigarettes and other tobacco products. Temperatures in burning cigarettes range from about 400 °C between puffs to about 900 °C during a puff. During the burning of the cigarette tobacco, thousands of chemical substances are generated by combustion, distillation, pyrolysis and pyrosynthesis. Tobacco smoke is used as a fumigant and inhalant.
Tobacco smoking is the practice of burning tobacco and ingesting the resulting smoke. The smoke may be inhaled, as is done with cigarettes, or simply released from the mouth, as is generally done with pipes and cigars. The practice is believed to have begun as early as 5000–3000 BC in Mesoamerica and South America. Tobacco was introduced to Eurasia in the late 17th century by European colonists, where it followed common trade routes. The practice encountered criticism from its first import into the Western world onwards but embedded itself in certain strata of a number of societies before becoming widespread upon the introduction of automated cigarette-rolling apparatus.
Passive smoking is the inhalation of tobacco smoke, called passive smoke, secondhand smoke (SHS) or environmental tobacco smoke (ETS), by individuals other than the active smoker. It occurs when tobacco smoke diffuses into the surrounding atmosphere as an aerosol pollutant, which leads to its inhalation by nearby bystanders within the same environment. Exposure to secondhand tobacco smoke causes many of the same health effects caused by active smoking, although to a lower prevalence due to the reduced concentration of smoke that enters the airway.
Cotinine is an alkaloid found in tobacco and is also the predominant metabolite of nicotine, typically used as a biomarker for exposure to tobacco smoke. Cotinine is currently being studied as a treatment for depression, post-traumatic stress disorder (PTSD), schizophrenia, Alzheimer's disease and Parkinson's disease. Cotinine was developed as an antidepressant as a fumaric acid salt, cotinine fumarate, to be sold under the brand name Scotine, but it was never marketed.
Tar is the name for the resinous, combusted particulate matter made by the burning of tobacco and other plant material in the act of smoking. Tar is toxic and damages the smoker's lungs over time through various biochemical and mechanical processes. Tar also damages the mouth by rotting and blackening teeth, damaging gums, and desensitizing taste buds. Tar includes the majority of mutagenic and carcinogenic agents in tobacco smoke. Polycyclic aromatic hydrocarbons (PAH), for example, are genotoxic and epoxidative.
Nicotine-derived nitrosamine ketone (NNK) is one of the key tobacco-specific nitrosamines derived from nicotine. It plays an important role in carcinogenesis. The conversion of nicotine to NNK entails opening of the pyrrolidine ring.
N-Nitrosonornicotine (NNN) is a tobacco-specific nitrosamine produced during the curing and processing of tobacco.
Tobacco products, especially when smoked or used orally, have serious negative effects on human health. Smoking and smokeless tobacco use is the single greatest cause of preventable death globally. As many as half of people who smoke tobacco or use it orally die from complications related to such use. It has been estimated that each year, in total about 6 million people die from tobacco-related causes, with 600,000 of these occurring in non-smokers due to secondhand smoke. It is further estimated to have caused 100 million deaths in the 20th century.
Smokeless tobacco is a tobacco product that is used by means other than smoking. Their use involves chewing, sniffing, or placing the product between gum and the cheek or lip. Smokeless tobacco products are produced in various forms, such as chewing tobacco, snuff, snus, and dissolvable tobacco products. Smokeless tobacco is widely used in South Asia and this accounts for about 80% of global consumption. All smokeless tobacco products contain nicotine and are therefore highly addictive. Quitting smokeless tobacco use is as challenging as smoking cessation.
Sidestream smoke is smoke which goes into the air directly from a burning cigarette, cigar, or smoking pipe. Sidestream smoke is the main component of second-hand smoke (SHS), also known as Environmental Tobacco Smoke (ETS) or passive smoking. The relative quantity of chemical constituents of sidestream smoke are different from those of directly inhaled ("mainstream") smoke, although their chemical composition is similar. Sidestream smoke has been classified as a Class A carcinogen by the U.S. Environmental Protection Agency.
In molecular genetics, a DNA adduct is a segment of DNA bound to a cancer-causing chemical. This process could lead to the development of cancerous cells, or carcinogenesis. DNA adducts in scientific experiments are used as biomarkers of exposure. They are especially useful in quantifying an organism's exposure to a carcinogen. The presence of such an adduct indicates prior exposure to a potential carcinogen, but it does not necessarily indicate the presence of cancer in the subject animal.
Tobacco harm reduction (THR) is a public health strategy to lower the health risks to individuals and wider society associated with using tobacco products. It is an example of the concept of harm reduction, a strategy for dealing with the use of drugs. Tobacco smoking is widely acknowledged as a leading cause of illness and death, and reducing smoking is vital to public health.
Tobacco-specific nitrosamines (TSNAs) comprise one of the most important groups of carcinogens in tobacco products, particularly cigarettes and fermented dipping snuff.
Ventilated cigarettes are considered to have a milder flavor than regular cigarettes. These cigarette brands may be listed as having lower levels of tar ("low-tar"), nicotine, or other chemicals as "inhaled" by a "smoking machine". However, the scientific evidence is that switching from regular to light or low-tar cigarettes does not reduce the health risks of smoking or lower the smoker's exposure to the nicotine, tar, and carcinogens present in cigarette smoke.
Tobacco smoking during pregnancy causes many detrimental effects on health and reproduction, in addition to the general health effects of tobacco. A number of studies have shown that tobacco use is a significant factor in miscarriages among pregnant smokers, and that it contributes to a number of other threats to the health of the foetus.
Animals are exposed to tobacco smoke and other cigarette by-products through their use as experimental subjects and through contact with smokers, as in the case of pets in houses where smoking takes place.
The health effects of electronic cigarettes (e-cigarettes) include a range of potential risks such as exposure to toxic chemicals, the possibility of increased likelihood of respiratory and cardiovascular diseases, and concerns about their possible role in cancer development. Upon their introduction, there were marketing claims that they were a safer alternative to traditional tobacco products.
The chemical composition of the electronic cigarette aerosol varies across and within manufacturers. Limited data exists regarding their chemistry. However, researchers at Johns Hopkins University analyzed the vape clouds of popular brands such as Juul and Vuse, and found "nearly 2,000 chemicals, the vast majority of which are unidentified."