This article needs additional citations for verification .(February 2022)
|Part of a series on|
|Personal and social effects|
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 (itself a complex mixture), thousands of chemical substances are generated by combustion, distillation, pyrolysis and pyrosynthesis. Tobacco smoke is used as a fumigant and inhalant.
The particles in tobacco smoke are liquid aerosol droplets (about 20% water), with a mass median aerodynamic diameter (MMAD) that is submicrometer (and thus, fairly "lung-respirable" by humans). The droplets are present in high concentrations (some estimates are as high as 1010 droplets per cm3). Most cigarettes today contain a cigarette filter, which can reduce "tar" and nicotine smoke yields up to 50%[ clarification needed ] by several different mechanisms, with an even greater removal rate for other classes of compounds (e.g., phenols). [ clarification needed ]
Tobacco smoke may be grouped into a particulate phase (trapped on a glass-fiber pad, and termed "TPM" (total particulate matter)) and a gas/vapor phase (which passes through such a glass-fiber pad). "Tar" is mathematically determined by subtracting the weight of the nicotine and water from the TPM. However, several components of tobacco smoke (e.g., hydrogen cyanide, formaldehyde, phenanthrene, and pyrene) do not fit neatly into this rather arbitrary classification, because they are distributed among the solid, liquid and gaseous phases.
Tobacco smoke contains a number of toxicologically significant chemicals and groups of chemicals, including polycyclic aromatic hydrocarbons (benzopyrene), tobacco-specific nitrosamines (NNK, NNN), aldehydes (acrolein, formaldehyde), carbon monoxide, hydrogen cyanide, nitrogen oxides (nitrogen dioxide), benzene, toluene, phenols (phenol, cresol), aromatic amines (nicotine, ABP (4-aminobiphenyl)), and harmala alkaloids. The radioactive element polonium-210 is also known to occur in tobacco smoke.The chemical composition of smoke depends on puff frequency, intensity, volume, and duration at different stages of cigarette consumption.
Between 1933 and the late 1940s, the yields from an average cigarette varied from 33 to 49 mg "tar" and from less than 1 to 3 mg nicotine. In the 1960s and 1970s, the average yield from cigarettes in Western Europe and the USA was around 16 mg tar and 1.5 mg nicotine per cigarette. Current average levels are lower. This has been achieved in a variety of ways including use of selected strains of tobacco plant, changes in agricultural and curing procedures, use of reconstituted sheets (reprocessed tobacco leaf wastes), incorporation of tobacco stalks, reduction of the amount of tobacco needed to fill a cigarette by expanding it (like puffed wheat) to increase its "filling power", and by the use of filters and high-porosity wrapping papers. The development of lower "tar" and nicotine cigarettes has tended to yield products that lacked the taste components to which the smoker had become accustomed. In order to keep such products acceptable to the consumer, the manufacturers reconstitute aroma or flavor.
Tobacco polyphenols (e. g., caffeic acid, chlorogenic acid, scopoletin, rutin) determine the taste and quality of the smoke. Freshly cured tobacco leaf is unfit for use because of its pungent and irritating smoke. After fermentation and aging, the leaf delivers mild and aromatic smoke.
|Compounds||In processed tobacco, per gram||In mainstream smoke, per cigarette||IARC evaluation of evidence of carcinogenicity|
|In laboratory animals||In humans|
|Polycyclic aromatic hydrocarbons|
|Benzo(a)pyrene||0.1–90 ng||20–40 ng||sufficient||probable|
|N-Nitrosodimethylamine||0–215 ng||0.1–180 ng||sufficient|
|N-Nitrosonornicotine||0.3–89 μg||0.12–3.7 μg||sufficient|
|4-(Methylnitrosamino)-1-(3-pyridyl)-1-butanone||0.2–7 μg||0.08–0.77 μg||sufficient|
|N-Nitrosoanabasine||0.01–1.9 μg||0.14–4.6 μg||limited|
|Formaldehyde||1.6–7.4 μg||70–100 μg||sufficient|
|Acetaldehyde||1.4–7.4 μg||18–1400 μg||sufficient|
|Crotonaldehyde||0.2–2.4 μg||10–20 μg|
|Miscellaneous organic compounds|
|Ethyl carbamate||310–375 ng||20–38 ng||sufficient|
|Vinyl chloride||1–16 ng||sufficient||sufficient|
|Hydrazine||14–51 ng||24–43 ng||sufficient||inadequate|
|Arsenic||500–900 ng||40–120 ng||inadequate||sufficient|
|Nickel||2000–6000 ng||0–600 ng||sufficient||limited|
|Chromium||1000–2000 ng||4–70 ng||sufficient||sufficient|
|Cadmium||1300–1600 ng||41–62 ng||sufficient||limited|
|Lead||8–10 μg||35–85 ng||sufficient||inadequate|
|Polonium-210||0.2–1.2 pCi||0.03–1.0 pCi||sufficient||sufficient|
Tobacco smoke, besides being an irritant and significant indoor air pollutant, is known to cause lung cancer, heart disease, chronic obstructive pulmonary disease (COPD), emphysema, and other serious diseases in smokers (and in non-smokers as well). The actual mechanisms by which smoking can cause so many diseases remain largely unknown. Many attempts have been made to produce lung cancer in animals exposed to tobacco smoke by the inhalation route, without success. It is only by collecting the "tar" and repeatedly painting this on to mice that tumors are produced, and these tumors are very different from those tumors exhibited by smokers.Tobacco smoke is associated with an increased risk of developing respiratory conditions such as bronchitis, pneumonia, and asthma. Tobacco smoke aerosols generated at temperatures below 400 °C did not test positive in the Ames assay.
In spite of all changes in cigarette design and manufacturing since the 1960s, the use of filters and "light" cigarettes has neither decreased the nicotine intake per cigarette, nor has it lowered the incidence of lung cancers (NCI, 2001; IARC 83, 2004; U.S. Surgeon General, 2004).The shift over the years from higher- to lower-yield cigarettes may explain the change in the pathology of lung cancer. That is, the percentage of lung cancers that are adenocarcinomas has increased, while the percentage of squamous cell cancers has decreased. The change in tumor type is believed to reflect the higher nitrosamine delivery of lower-yield cigarettes and the increased depth or volume of inhalation of lower-yield cigarettes to compensate for lower level concentrations of nicotine in the smoke.
In the United States, lung cancer incidence and mortality rates are particularly high among African American men. Lung cancer tends to be most common in developed countries, particularly in North America and Europe, and less common in developing countries, particularly in Africa and South America. [ clarification needed ]
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 an herbal cigarette. A cigarette is distinguished from a cigar by its usually smaller size, use of processed leaf, and paper wrapping, which is typically white. Since the 1920s, cigarettes have been a major source of advertising revenue for the media, of traffic for small stores, and of tax revenue for governments.
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.
Tobacco products, especially when smoked or used orally, have negative effects on human health, and concerns about these effects have existed for a long time. Research has focused primarily on cigarette smoking.
A cigarette filter, also known as a filter tip, is a component of a cigarette, along with cigarette paper, capsules and adhesives. Filters were introduced in the early 1950s.
Herbal cigarettes are cigarettes that usually do not contain any tobacco or nicotine, instead being composed of a mixture of various herbs and/or other plant material. However, Chinese herbal cigarettes contain tobacco and nicotine with herbs added, unlike European and North American herbal cigarettes which have tobacco and nicotine omitted. Like herbal smokeless tobacco, they are often used as a substitute for standard tobacco products. Herbal cigarettes are often advertised as a smoking cessation aid. They are also used in acting scenes by performers who are non-smokers, or where anti-smoking legislation prohibits the use of tobacco in public spaces. Herbal cigarettes can carry carcinogens.
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.
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.
Third-hand smoke is contamination by tobacco smoke that lingers following the extinguishing of a cigarette, cigar, or other combustible tobacco product. 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.
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.
The tar derby is the period in the 1950s marked by a rapid influx in both cigarette advertising focused on tar content measurements to differentiate cigarettes and brand introduction or repositioning focusing on filter technology. The period ended in 1959 after the Federal Trade Commission (FTC) Chairman and several cigarette company presidents agreed to discontinue usage of tar or nicotine levels in advertisements.
Smoking in Iceland is banned in restaurants, cafés, bars and night clubs as of June 2007. A large majority of Icelanders approve of the ban. At the time the ban went into effect, almost one in four Icelandic people were smokers.
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 use of electronic cigarettes (vaping) carries health risks. The risk depends on the fluid and varies according to design and user behavior. In the United Kingdom, vaping is considered by some to be around 95% less harmful than tobacco after a controversial landmark review by Public Health England.
The scientific community in the United States and Europe are primarily concerned with the possible effect of electronic cigarette use on public health. There is concern among public health experts that e-cigarettes could renormalize smoking, weaken measures to control tobacco, and serve as a gateway for smoking among youth. The public health community is divided over whether to support e-cigarettes, because their safety and efficacy for quitting smoking is unclear. Many in the public health community acknowledge the potential for their quitting smoking and decreasing harm benefits, but there remains a concern over their long-term safety and potential for a new era of users to get addicted to nicotine and then tobacco. There is concern among tobacco control academics and advocates that prevalent universal vaping "will bring its own distinct but as yet unknown health risks in the same way tobacco smoking did, as a result of chronic exposure", among other things.
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."
A heated tobacco product (HTP) is a tobacco product that heats the tobacco at a lower temperature than conventional cigarettes. These products contain nicotine, which is a highly addictive chemical. The heat generates an aerosol or smoke to be inhaled from the tobacco, which contains nicotine and other chemicals. HTPs may also contain additives not found in tobacco, including flavoring chemicals. HTPs generally heat tobacco to temperatures under 600 °C (1100 °F), a lower temperature than conventional cigarettes.
The composition of the emissions generated from heated tobacco products are generally lower than that found in cigarette smoke. This is due to the comparatively low temperatures, the filter systems, and physical design. The composition of what is produced is complex. The main toxicants found in the emissions of cigarette smoke are also found in the emissions of these products in varying concentrations. The aerosol generated contains levels of nicotine and cancer-causing chemicals that are comparable to regular cigarettes. The emissions contained 84% of the nicotine found in regular cigarettes.