Health effects of electronic cigarettes

|alt=Switching from tobacco to vaping may reduce weight gain after smoking cessation, increase exercise tolerance, reduce exposure to toxic chemicals, and reduce risk of death. Vaping may reduce shortness of breath, reduce coughing, reduce spitting, and reduce sore throat compared to tobacco. Harm reduction refers to the reduction of the public's negative view towards certain behaviors. When a person does not want to quit nicotine, harm minimization means striving to eliminate tobacco exposure by replacing it with vaping. E-cigarettes can reduce smokers' exposure to carcinogens and other toxic chemicals found in tobacco. E-cigarettes produce similar levels of particulates to tobacco cigarettes. Tobacco harm reduction has been a controversial area of tobacco control. Health advocates have been slow to support a harm reduction method out of concern that tobacco companies cannot be trusted to sell products that will lower the risks associated with tobacco use. Tobacco smoke contains 100 known carcinogens and 900 potentially cancer-causing chemicals, but e-cigarette vapor contains fewer potential carcinogens than tobacco smoke. A 2025 review of 39 studies found "no significant incident or prevalent risk" of cancer from vaping. Due to their similarity to traditional cigarettes, e-cigarettes could play a valuable role in tobacco harm reduction. A 2025 study that analyzed data from the National Vital Statistics System (NVSS), the Behavioral Risk Factor Surveillance System (BRFSS), the National Health Interview Survey (NHIS), and the National Survey on Drug Use and Health (NSDUH) concluded that e-cigarettes had preserved 677,000 life–years from 2011 to 2019. Evidence to substantiate the potential of vaping to lower tobacco-related death and disease is unknown. E-cigarettes could have an influential role in tobacco harm reduction. A 2014 review recommended that regulations for e-cigarettes could be similar to those for dietary supplements or cosmetic products to not limit their potential for harm reduction. There is no research available on vaping for reducing harm in high-risk groups such as people with mental disorders. A 2014 PHE report concluded that hazards associated with products currently on the market are probably low, and apparently much lower than smoking. The British Medical Association encourages health professionals to recommend conventional nicotine replacement therapies, but for patients unwilling to use or continue using such methods, health professionals may present e-cigarettes as a lower-risk option than tobacco smoking. The American Association of Public Health Physicians (AAPHP) suggests those who are unwilling to quit tobacco smoking or unable to quit with medical advice and pharmaceutical methods should consider other nicotine-containing products such as e-cigarettes and smokeless tobacco for long-term use instead of smoking. == Smoking cessation ==

Whether e-cigarettes help people quit smoking is debated. Limited evidence suggests that e-cigarettes likely do help people to stop smoking when used in clinical settings. Outside clinical settings, vaping does not greatly change the odds of quitting smoking. A small number of studies have looked at whether using e-cigarettes reduces the number of cigarettes smokers consume. but smoking just one to four cigarettes daily greatly increases the risk of cardiovascular disease compared to not smoking. It is unclear whether e-cigarettes are only helpful for particular types of smokers. Vaping with nicotine may reduce tobacco use among daily smokers. Whether vaping is effective for quitting smoking may depend on whether it was used as part of an effort to quit. One of the challenges in studying e-cigarettes is that there are hundreds of brands and models of e-cigarettes sold. These vary in design, operation, and composition of the liquid, and the technology continues to change. E-cigarettes have not been subjected to the same type of efficacy testing as nicotine replacement products. There are also social concerns - use of e-cigarettes may normalize tobacco use and prolong cigarette use for people who could have quit, and it could put extra pressure on smokers to stop cigarette smoking because e-cigarettes are a more socially acceptable alternative. There is low-quality evidence that vaping assists smokers to quit smoking in the long-term compared with nicotine-free vaping. E-cigarettes without nicotine may reduce tobacco cravings because of the smoking-related physical stimuli. A 2016 review found low-quality evidence of a trend towards benefit of e-cigarettes with nicotine for smoking cessation. Tentative evidence indicates that health warnings on vaping products may influence users to give up vaping. As of 2020, the efficacy and safety of vaping for quitting smoking during pregnancy was unknown. No research is available to provide details on the efficacy of vaping for quitting smoking during pregnancy. There is robust evidence that vaping is not effective for quitting smoking among adolescents. In view of the shortage of evidence, vaping is not recommend for cancer patients, although for all patients vaping is likely less dangerous than smoking cigarettes. The effectiveness of vaping for quitting smoking among vulnerable groups is uncertain. == Safety ==

There is no consensus on the risks of e-cigarette use. There is little data about their safety, and a considerable variety of liquids are used as carriers, and thus are present in the aerosol delivered to the user. whereas another found that vaping is associated with chronic obstructive pulmonary disease but less so than smoking. but e-cigarettes are safer than combusted tobacco products However, e-cigarette use with or without nicotine cannot be considered risk-free because the long-term effects of e-cigarette use are unknown. There is "only limited evidence showing adverse respiratory and cardiovascular effects in humans", with the authors of a 2020 review calling for more long-term studies on the subject.|alt=Possible side effects of nicotine include increased clotting tendency, atherosclerosis, enlargement of the aorta, bronchospasm, muscular tremor and pain, gastrointestinal nausea, dry mouth, dyspepsia, diarrhea, heartburn, peptic ulcer, cancer, lightheadedness, headache, sleep disturbances, abnormal dreams, irritability, dizziness, blood restriction, increased or decreased heart rate, increased blood pressure, tachycardia, more (or less) arrhythmias, coronary artery constriction, coronary artery disease, high insulin, insulin resistance, and risks to the child later in life during pregnancy include type 2 diabetes, obesity, hypertension, neurobehavioral defects, respiratory dysfunction, and infertility. The cytotoxicity of e-liquids varies, and contamination with various chemicals have been detected in the liquid. Metal parts of e-cigarettes in contact with the e-liquid can contaminate it with metal particles. Nicotine is associated with cardiovascular disease and poisoning, and possibly with birth defects. In 2021, researchers at Johns Hopkins University reported over 2,000 unknown chemicals in the vape clouds that they tested from Vuse, Juul, Blu and Mi-Salt vape devices. E-cigarettes create vapor that consists of fine and ultrafine particles of particulate matter, with the majority of particles in the ultrafine range. The majority of toxic chemicals found in cigarette smoke are absent in e-cigarette vapor. E-cigarette vapor contains lower concentrations of potentially toxic chemicals than with cigarette smoke. Those which are present, are mostly below 1% of the corresponding levels permissible by workplace safety standards. But workplace safety standards do not recognize exposure to certain vulnerable groups such as people with medical ailments, children, and infants who may be exposed to second-hand vapor. although e-cigarette pollutant levels are much lower than for cigarettes and likely to pose a much lower risk, if any, compared to cigarettes. A 2014 review recommended that e-cigarettes should be regulated for consumer safety. E-cigarettes that are not reusable may contribute to the problem of electronic waste. == Addiction ==

Nicotine, a key ingredient in most e-liquids, Addiction is believed to be a disorder of experience-dependent brain plasticity. The reinforcing effects of nicotine play a significant role in the beginning and continuing use of the drug. First-time nicotine users develop a dependence about 32% of the time. Chronic nicotine use involves both psychological and physical dependence. Nicotine-containing e-cigarette vapor induces addiction-related neurochemical, physiological and behavioral changes. Nicotine affects neurological, neuromuscular, cardiovascular, respiratory, immunological and gastrointestinal systems. Neuroplasticity within the brain's reward system occurs as a result of long-term nicotine use, leading to nicotine dependence. The neurophysiological activities that are the basis of nicotine dependence are intricate. Nicotine addiction is a disorder which alters different neural systems such as dopaminergic, glutamatergic, GABAergic, serotoninergic, that take part in reacting to nicotine. Long-term nicotine use affects a broad range of genes associated with neurotransmission, signal transduction, and synaptic architecture. , such as nicotine, are associated with its ability to excite the mesolimbic and dopaminergic systems.How does the nicotine in e-cigarettes affect the brain? Until about age 25, the brain is still growing. that binds to and activates nicotinic acetylcholine receptors in the brain, and several neuropeptides, including proopiomelanocortin-derived α-MSH and adrenocorticotropic hormone. Corticotropin-releasing factor, Neuropeptide Y, orexins, and norepinephrine are involved in nicotine addiction. Continuous exposure to nicotine can cause an increase in the number of nicotinic receptors, which is believed to be a result of receptor desensitization and subsequent receptor upregulation. Long-term nicotine exposure upregulates cortical nicotinic receptors, but it also lowers the activity of the nicotinic receptors in the cortical vasodilation region. With constant use of nicotine, tolerance occurs at least partially as a result of the development of new nicotinic acetylcholine receptors in the brain. Nicotine also stimulates nicotinic acetylcholine receptors in the adrenal medulla, resulting in increased levels of epinephrine and beta-endorphin. When trying to quit smoking with vaping a base containing nicotine, symptoms of withdrawal can include irritability, restlessness, poor concentration, anxiety, depression, and hunger. E-cigarettes may reduce cigarette craving and withdrawal symptoms. It is not clear whether e-cigarette use will decrease or increase overall nicotine addiction, but the nicotine content in e-cigarettes is adequate to sustain nicotine dependence. Chronic nicotine use causes a broad range of neuroplastic adaptations, making quitting hard to accomplish. Experienced users tend to take longer puffs which may result in higher nicotine intake. The National Institute on Drug Abuse said e-cigarettes could maintain nicotine addiction in those who are attempting to quit. The limited available data suggests that the likelihood of excessive use of e-cigarettes is smaller than traditional cigarettes. No long-term studies have been done on the effectiveness of e-cigarettes in treating tobacco addiction, Adolescents are likely to underestimate nicotine's addictiveness. Vulnerability to the brain-modifying effects of nicotine, along with youthful experimentation with e-cigarettes, could lead to a lifelong addiction. A long-term nicotine addiction from using a vape may result in using other tobacco products. The majority of addiction to nicotine starts during youth and young adulthood. Adolescents are more likely to become nicotine dependent than adults. as is the extent to which e-cigarette use may lead to addiction or substance dependence in young people. == Positions ==

The scientific community in US and Europe are primarily concerned with their possible effect 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 young people. 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. Medical organizations differ in their views about the health implications of vaping. There is general agreement that e-cigarettes expose users to fewer toxicants than tobacco cigarettes. Healthcare organizations in the UK (including the Royal College of Physicians and Public Health England) have encouraged smokers to switch to e-cigarettes or other nicotine replacements if they cannot quit, as this would potentially save millions of lives. In 2016, the US Food and Drug Administration (US FDA) stated that "Although ENDS [electronic nicotine delivery systems] may potentially provide cessation benefits to individual smokers, no ENDS have been approved as effective cessation aids." In 2019 the European Respiratory Society stated that "[t]he tobacco harm reduction strategy is based on well-meaning but incorrect or undocumented claims or assumptions." Medical organizations avoid releasing statements about the relative toxicity of electronic cigarettes because of the many different device types, liquid formulations, and new devices that come onto the market. Some healthcare groups and policy makers have hesitated to recommend e-cigarettes with nicotine for quitting smoking, despite some evidence of effectiveness (when compared to Nicotine Replacement Therapy or e-cigarettes without nicotine) and safety. In August 2014, the Forum of International Respiratory Societies, which represents multiple pulmonary associated medical associations in the United States, Latin America, Africa, Europe, and Asia, released a statement in which they argued that e-cigarettes have not been demonstrated to be safe and their benefits as a smoking cessation tool or in harm reduction has not been adequately studied. In May 2018, the Forum of International Respiratory Societies released a position statement, stating "ENDS are devices that deliver aerosols of nicotine and other volatile chemicals to the lung. Their use has rapidly escalated among youths and they are now the most commonly used tobacco product among adolescents. Initiation of electronic cigarette use is strongly associated with the subsequent initiation of combustible tobacco product use among adolescents." In January 2014, the International Union Against Tuberculosis and Lung Disease released a statement asserting that the benefits and safety of e-cigarettes have not been scientifically proven. The World Lung Foundation (now known as Vital Strategies) applauded the 2014 WHO report's recommendation for tighter regulation of e-cigarettes due to concerns about the safety of e-cigarettes and the possible increased nicotine or tobacco addiction among youth. Canada Health Canada states in relation to the Tobacco and Vaping Products Act which became law on May 23, 2018, that "vaping is less harmful than smoking. The Canadian Cancer Society has concluded, e-cigarettes "have not been scientifically proven to help people quit" smoking tobacco. The Canadian Heart and Stroke Foundation has stated, "While early studies show some potential benefits, the effectiveness of e-cigarettes with nicotine as a smoking cessation device is not fully conclusive," and expressed concerns about the lack of long-term studies with regard to health effects to the user as well as second-hand exposure. Tobacco-flavor is the only flavor allowed and ecigs cannot be sold online. 2.7 million people die each year due to smoking. The Philippine Medical Association has also taken a strong position against the use of electronic cigarettes, citing safety concerns. Europe In 2019 the European Respiratory Society stated that "The long-term effects of ECIG use are unknown, and there is therefore no evidence that ECIGs are safer than tobacco in the long term." France In 2022, French health body le Haut Conseil de la santé publique (HCSP) said that health professionals should not recommend e-cigarettes for quitting, as there was not enough information on risks and benefits. Smokers trying to quit in France should not be offered vapes to help Germany The German Cancer Research Center in Germany released a report in 2013 stating that e-cigarettes cannot be considered safe, in part due to technical flaws that have been found as well as unreliable information about product quality, including information provided by manufacturers. Spain The Spanish Society of Pneumonology and Thoracic Surgery (SEPAR) released a position statement which states that the substances found in aerosol from e-cigarettes have not been demonstrated to be safe, and a number of chemicals which are carcinogens and can damage the lung have been found, though usually in concentrations smaller than conventional cigarettes. United Kingdom A 2018 Public Health England report reiterated the approximation that e-cigarettes are 95% less harmful than smoking. United States Government agencies Following five confirmed deaths in the US, on September 6, 2019, the Centers for Disease Control and Prevention stated that while this investigation is ongoing, people should consider not using e-cigarette products. In 2016, the US Food and Drug Administration (FDA) stated that "Although ENDS [electronic nicotine delivery systems] may potentially provide cessation benefits to individual smokers, no ENDS have been approved as effective cessation aids." Medical societies On September 9, 2019, following an upsurge of reports of lung disease associated with vaping, the American Medical Association issued a statement saying "In light of increasing reports of e-cigarette-associated lung illnesses across the country, the AMA urges the public to avoid the use of e-cigarette products until health officials further investigate and understand the cause of these illnesses." The next day the American Lung Association issued a warning, saying "E-cigarettes are not safe and can cause irreversible lung damage and lung disease. No one should use e-cigarettes or any other tobacco product. This message is even more urgent today following the increasing reports of vaping-related illnesses and deaths nationwide." On November 19, 2019, the American Medical Association urged for a complete ban on all types of vaping products that are not approved by the US FDA as quitting smoking aids. ==Risk context==

When evaluating the health effects of some activity, a reasonable question is "what is the practical alternative?" If the alternatives are worse, then the activity must be measured against the alternatives. If the alternative is smoking, the answer might be different than if the alternative is simply to avoid nicotine. This is because the health impacts of smoking are strongly negative, while the impacts of avoiding nicotine entirely are positive. Smoking E-cigarette vapor does not contain tobacco and does not involve combustion, therefore users do not encounter several harmful constituents of tobacco smoke, A 2014 review concluded that e-cigarette aerosol contains far fewer carcinogens than tobacco smoke, and concluded that e-cigarettes "impart a lower potential disease burden" than traditional cigarettes. Smokers can use e-cigarettes for various purposes. As an aid to quitting smoking, vaping is a temporary activity that reduces smoking and terminates once the smoker has completed the transition away from nicotine. To the extent that vaping aids the transition, its health effects are positive. Alternatively, smokers can substitute vaping for smoking without intending to transition. In this context, vaping is still preferred. However, if vaping is used as a way to get nicotine in situations where smoking is not convenient, vaping may negatively affect health. Other smoker-transition aids are available and may offer better safety and/or effectiveness profiles then vaping. Given equal effectiveness, relatively safety considerations would become paramount. However, a large-scale 2025 analysis indicated that other smoking cessation products are less effective at aiding transition than vaping. Abstinence Vaping presents health risks that are definitionally higher than those of simple abstinence, as no independent health benefits have been reported, while nicotine and cannabis have well-established harms. This comparison is relevant because some never-smokers adopt e-cigarettes for these drugs. Once dependence is established, users may be more likely to take up smoking. == Individual effects ==

Health effects for non-smokers must be considered in absolute terms for long-term use as well as the risk of transition into traditional cigarettes, while for smokers the relative risks are paramount, and if used as a quitting aid, any short-term effects are most important. Non-smokers E-cigarettes create nicotine dependence in non-smokers. Pregnant or nursing women and the elderly are more sensitive to nicotine than other individuals. Smokers Used to transition to abstinence, e-cigarettes end the consumption of nicotine and the other harmful substances in tobacco smoke and later any harmful e-liquid ingredient. However, if abstinence is not achieved, e-cigarettes could mean increased nicotine dependence (by adding vaping to smoking) and ongoing harm from other e-liquid ingredients. Health benefits associated with transitioning from smoking to vaping include decreased post-smoking weight gain and improved exercise tolerance. Even a partially successful transition may allow smokers to reduce their cigarette consumption with related health benefits. A 2022 Cochrane review concluded that vaping increased quit rates compared to e-cigarettes without nicotine and compared to nicotine replacement therapy, although it did not compare vaping to other methods. How much safer electronic are versus conventional cigarettes is disputed. 2015 and 2018 Public Health England (PHE) reports claimed that vaping is "at least 95% less harmful than smoking". The Royal College of Physicians, the Royal Society for Public Health, and the National Health Service backed these claims. The estimate was limited by "lack of hard evidence for the harms of most products on most of the criteria". lack of specific evidence, Reviews in 2016 and 2018 claimed that the harm from e-cigarettes is much higher than the "95% safer" figure. reported that e-cigarettes sold in England (which allow nicotine strength of no more than 20 mg/ml) are unlikely to exceed 5% of the harm of cigarettes for non-pregnant adults. This claim is consistent with the 2018 view of the US National Academies of Sciences, Engineering, and Medicine. General Device defects can result in e.g., battery explosions and may cause burns or other injuries. Concentrated e-liquid exposure can come by leaks or spills. Nicotine poisoning can occur by ingestion, inhalation, or absorption via the skin or eyes. A 2018 review concluded that exposure to second-hand vapor can reduce lung function. A 2015 review concluded that adverse effects are mostly associated with short-term use and the reported adverse effects decreased over time. Neurological Many effects on the nervous and the sensory systems are possibly related to nicotine overdose or withdrawal. A 2016 study reported that an e-liquid containing 23% alcohol was linked to reduced performance on the Purdue Pegboard Test. A 2017 study reported harm to neurons along with tremors and spasms. Injuries (USFA) report entitled Electronic Cigarette Fires and Explosions. or misused. E-liquid ingredients may be flammable. A 2014 review claimed that some users add more or larger batteries to nonadjustable e-cigarettes, which may lead to battery leakage or explosion. Another 2016 study assembled reports of 92 explosion, fire, or overheating events, with related injuries in 47 individuals. Prominent harms included 2 cervical vertebral fractures, 1 palate fracture, 3 instances of damaged teeth, 33 thermal burns, 4 chemical burns, and 5 lacerations. In 2018 PHE reported six UK case studies involving e-cigarettes with burns. Explosions have resulted in lost teeth, neck fractures, and burns from combustion and/or battery acid. Reported burns covered from 1% to 8% of body area. They were most commonly reported in the lower extremity, hands, head and neck, and genitalia. Explosions in some cases produced 2nd and 3rd degree burns. A 2018 review concluded that some 50% needed surgical management. Burn risk extends to bystanders. Burn events while on home oxygen therapy have been reported, leading Health Canada in 2014 to warn of fire risk. The heating element in vaping devices can get hot enough to ignite in the presence of oxygen. Poisoning related to e-cigarette calls to US poison control centers E-cigaratte nicotine poisoning occurs via ingestion, inhalation, or absorption via the skin or eyes. As of 2016 four adults were reported to have died in the US and Europe after intentionally ingesting e-liquid. Two children, one in the US in 2014 and another in Israel in 2013, died after ingesting liquid nicotine. A two-year-old girl in the UK in 2014 was hospitalized after licking an e-cigarette liquid refill. A 2022 concluded that toxicity can come from aerosols containing toxic chemicals or excessive concentrations of nicotine as an e-liquid. A 2016 study reported minor, moderate, and serious adverse effects. Minor effects correlated with e-liquid poisoning were tachycardia, tremor, chest pain and hypertension. More serious effects were bradycardia, hypotension, nausea, respiratory paralysis, atrial fibrillation and dyspnea. Initial symptoms included rapid heart rate, sweating, feeling sick, and vomiting. Delayed symptoms included low blood pressure, seizures, and hypoventilation. Rare serious effects included coma, seizure, trouble breathing, and heart attack. After examining poison control centers' reports between 2010 and early 2019, FDA reported that, between the poison control centers and FDA, 35 cases of seizures mentioned use of e-cigarettes. From 2011 to 2019, cases of accidental poisoning from nicotine e-liquids grew rapidly in the US. From 1 September 2010, to 31 December 2014, 58% of e-cigarette calls to US poison control centers were related to children under 6. Severe outcomes were more than 2.5 times more frequent in children exposed to e-cigarettes and nicotine e-liquid than with traditional cigarettes. . A 2015 study reported that e-cigarette vapors can induce oxidative stress in lung endothelial cells. A 2014 case report observed the correlation between sub-acute bronchiolitis and vaping. A 2015 review reported that the long-term effects regarding respiratory flow resistance were unknown. A 2015 clinician's guide stated that 5 minutes of vaping considerably increased lung airflow resistance. A 2014 study reported higher levels of exhaled nitric oxide, which was associated with lung inflammation. A 2014 review concluded that harmful effects to cardiovascular and respiratory functions after short-term use of e-cigarettes were appreciably milder than traditional cigarettes. E-cigarette particles are small enough to enter the alveoli and to go deep in the lungs and enter into systemic circulation. A 2019 case study of hard-metal pneumoconiosis cannabis vapers reported cobalt, nickel, aluminum, manganese, lead, and chromium in the vapor. Metal-induced toxicity in the lung can result in long-term/permanent lung scarring. A 2018 review concluded that exposure to vapor has adverse effects on lungs and pulmonary function. Repeated acrolein exposure causes chronic pulmonary inflammation, reduction of host defense, neutrophil inflammation, mucus hypersecretion, and protease-mediated lung tissue damage, which are linked to the development of chronic obstructive pulmonary disease (COPD). It further reported that vapers experienced decreased expression of immune-related genes in their nasal cavities, more so than smokers. By contrast, vaping upregulates expression of platelet-activating factor receptor (PAFR) in nasal epithelial cells; PAFR is an important molecule involved in the ability of S. pneumoniae, (leading cause of bacterial pneumonia), to attach to cells. A 2016 study reported that adverse effects may include airway resistance, irritation of the airways, eyes redness, dry throat, and increase in allergic airway inflammation with elevated infiltration of inflammatory cells including eosinophils into airways. Vaping is associated with a positive association of vaping and chronic bronchitis among US high school juniors and seniors; which persisted among former users. Vaping was associated with an increased diagnosis of asthma and asthma-related school absences among Korean never-smoker high school students. A 2020/21 survey of 39,214 young people (aged 16 to 19) from the US, Canada, and England found that those who vaped were more likely to have breathing issues (breathlessness, wheezing, chest pain, phlegm, and cough) than those who did not. Also, the more young people vaped, the higher their chance of breathing issues. 2019–2020 vaping lung injury outbreak Cardiovascular A 2018 review concluded that the specific role of nicotine in cardiovascular disease had not been established. A 2024 review attributed cardiovascular effects to oxidative stress, inflammation, endothelial dysfunction, atherosclerosis, hemodynamic effects, and platelet function. A 2019 review reported limited evidence of vaping's adverse impacts on endothelial function and arterial hardening. A 2017 review concluded that vaping could exacerbate adverse cardiovascular effects among those who already have cardiovascular disease. Studies of aldehydes, particulates, and flavorings reported mixed impacts on cardiovascular health. A 2016 review concluded that vaping generates sympathomimetic effects. A 2016 review concluded that there could be a risk for conditions such as tachycardia-induced cardiomyopathy. Tight junctions (TJ) help with the construction and permeability of the barrier in the gut by firmly securing joints. Chronic, repetitive exposure to e-cigarettes damages this barrier by breaking the TJs, which causes gut inflammation, assage of bacteria. altering gene expression. A 2022 study reported that common GI health effects include nausea, vomiting, gastrointestinal discomfort, xerostomia, oral mucositis, gum bleeding, gingivitis, gastric burning, altered bowel habits, and acid reflux. Chronic exposure also drives inflammation in the colon. Nervous system A 2024 review concluded that nicotine exposure has detrimental effects on the nervous system, especially during adolescence. Exposure during developmental stages changes brain structure and function. Vaping is linked to impairment of cognitive processes, increased mood disorders and addiction, damage to functions such as memory, reasoning, impulse control, and attention. A 202 study reported lower gene expression, reducing occludin, which compromises the stability and strength of the blood-brain-barrier, resulting in neurovascular dysfunction, neuroinflammation, and cognitive defects. A 2010 study reported that short-term nicotine use excites the autonomic ganglia nerves and autonomic nerves. Oral cavity A 2018 review reported little evidence indicating that vaping is less damaging than smoking for periodontal disease j A 2017 review concluded that nicotine and flavorings may damage periodontal ligaments, stem cells, and gingival fibroblasts in cultures from aldehydes and/or carbonyls from vapor. A 2021 study reported that vaping resulted in nicotine stomatitis, hairy tongue, angular cheilitis, and oral mucosal lesions. E-cigarettes are not implicated in cancer. However, cannabinoid e-cigarettes mixed with other diluents and chemicals was associated with EVALI, == Public health effects ==

Various studies rate the public health impacts of vaping as far less negative than those of smoking. Second-hand vapor E-cigarette emissions are not comparable to cigarette smoke as their chemical composition is completely different. that form a visible fog. Vapor particles are larger than smoke particles, with a mean droplet size of 600 nm (inhaled) and 300 nm (exhaled) and could present a second-hand risk. A third reported that vapor may include propylene glycol aerosols at levels that can cause eye and respiratory irritation and exceed California Environmental Protection Agency standards. A 2017 study reported that people living with e‐cigarette users had increased salivary nicotine concentrations. health effects from exhaled vapor were known. A 2017 review concluded that the few studies that examined the effect of indoor air quality on human test subjects in natural settings produced inconsistent results. (vapor) exhaled by a vaper may expose non-users to second-hand vapor. Between January 2012 and December 2014, FDA published 35 adverse effect reports regarding second-hand vapor exposure. A 2018 study reported PM2.5 levels in a large hotel event room (4,023m3) increased from 2–3 μg/m3 to as high as 819 μg/m3 (interquartile range: 761–975 μg/m3) when 59–86 people were vaping. This level exceeded the US Environmental Protection Agency annual time-weighted standard for PM2.5 of 12 μg/m3. In 2014, several groups came out against e-cigarettes. The International Union Against Tuberculosis and Lung Disease stated, "Adverse health effects for exposed third parties (second-hand exposure) cannot be excluded because the use of e-cigarettes leads to emission of fine and ultrafine inhalable liquid particles, nicotine and cancer-causing substances into indoor air." The American Industrial Hygiene Association concluded that "e-cigarettes are not emission-free and that their pollutants could be of health concern for users and those who are exposed secondhand....[T]heir use in the indoor environment should be restricted, consistent with current smoking bans, until and unless research documents that they will not significantly increase the risk of adverse health effects to room occupants." Similarly, in 2016 the American Society of Heating, Refrigeration and Air-Conditioning Engineers (ASHRAE) updated its standard for "Ventilation for Acceptable Indoor Air Quality" to incorporate emissions from e-cigarettes into the definition of "environmental tobacco smoke," which is incompatible with acceptable indoor air quality. A 2017 French "experts statement" recommended banning vaping indoors in public and working areas. A 2014 WHO report stated passive exposure was a concern, indicating that current evidence is insufficient to determine whether the levels of exhaled vapor are safe to involuntarily exposed bystanders. Several medical organizations advocate that vaping be banned in public places and workplaces. A 2014 review concluded it is safe to infer that their effects on bystanders are minimal in comparison to traditional cigarettes. A 2017 study reported that some chemicals could violate workplace safety standards. A review of convention studies concluded that second-hand vapor may be significant, particularly for workers who repeatedly encounter it. Exposure studies suggest that indoor vaping is higher than the smoke-free level put forth by the US Surgeon General and the WHO Framework Convention on Tobacco Control. and are mostly below 1% of permissible levels. and local irritation can follow. Less than 1 tablespoon can cause adverse effects such as seizures, anoxic brain trauma, vomiting, lactic acidosis, A potentially fatal dose for a child is 0.1–0.2 mg/kg of body weight, A fatal dose for an adult is 0.5–1 mg/kg However the widely used human LD50 estimate of around 0.8 mg/kg was questioned in a 2013 review, in light of documented cases of humans surviving much higher doses; the lower fatal limit was 500–1000 mg of ingested nicotine, which is equivalent to 6.5–13 mg/kg orally. Vapor build-up E‐cigarettes can be unsafe to non-users via third-hand exposure, including children, pregnant women, nursing mothers, However, the extent of such contamination has not been established. A 2015 PHE report stated that an infant would have to lick 30 square meters to be exposed to 1 mg of nicotine. Risks to children Children are more likely to mistake a colorful e-liquid container for a juice container. The US mandates child-proof packaging. Self-harm As of 2019 a few incidents of intentional self-harm by ingesting or injecting e-liquids had been reported. Pets may find and bite them or expose themselves to the liquid refilling solution. In a 15 March 2016, letter to the editor of the Journal of the American Veterinary Medical Association, the Texas Poison Center Network reported 11 cases of dog exposures to e-cigarettes or refills. == Toxicology ==

The long-term health impacts of vaping are unknown, Limited peer-reviewed data restricts the scope of toxicological evaluation; their cytotoxicity is unknown. A 2014 review concluded that few e-cigarettes had undergone a thorough toxicology evaluation and testing. A 2013 study claimed that they were similar in toxicity to other nicotine replacement products, but this was disputed. Toxicant comparisons E-cigarettes supply nicotine and other toxins at rates far below traditional cigarettes and other nicotine delivery systems: DNA damage Nicotine has been reported to damage DNA, assessed by the Escherichia colipol A+/pol− test. A 2015 review concluded that nicotine decreases Chk2, a tumor suppressor, which is otherwise activated by DNA damage. A 2016 review concluded that vapor had adverse effects on primary airway epithelial cells and tumor cell lines, and other epithelial cell lines, that ranged from reducing viability, increase in production of inflammatory mediators and oxidative stress, reduced antimicrobial defences and increased pro-carcinogenic events. Propylene glycol and glycerin molecule The primary base ingredients of e-liquids are propylene glycol and glycerin. A 2016 study reported that 6% of nicotine, 8% of propylene glycol, and 16% of glycerin was exhaled. A 2017 review concluded that propylene glycol and glycerin increased the amount of hydrogen peroxide. possibly from heated glycerin. A 2017 review concluded that acrolein induces oxidative stress and inflammation, disrupting lung endothelial cell barrier function and may lead to chronic obstructive pulmonary disease. Recent in vitro research has demonstrated that nicotine-free e-cigarette vapor induces oxidative stress in human endothelial cells via activation of ARF6 and its guanine nucleotide exchange factor ARNO. This oxidative stress promotes abnormal angiogenic signalling and endothelial dysfunction, suggesting that vaping without nicotine may still contribute to vascular injury through reactive oxygen species pathways. Similar findings have been reported with nicotine-containing e-cigarette condensate, indicating that both nicotine-free and nicotine-containing vaping fluids can disrupt pulmonary endothelial function via ARF6-mediated mechanisms. Flavorings Flavored e-liquids contain additional substances in part to disguise nicotine's bitter taste. given limited toxicological data. Each flavoring has a different chemical composition. Many flavorings are irritants. Some flavorings are toxic and some resemble known carcinogens. The caffeine exposures from vaping are considerably less than caffeinated beverages. Limited information is available regarding the effects of inhaling caffeine. A 2017 review concluded that they were carcinogenic or toxic, and could contribute to cardiopulmonary diseases and neurodegenerative disorders. A 2019 study that sampled e-cigarette delivery systems reported that Juul pods were the only product to demonstrate in vitro cytotoxicity from both nicotine and flavoring chemical content, in particular ethyl maltol. The American Lung Association recommended in 2016 that the FDA require that diacetyl and other chemicals be banned from e-cigarettes. Exposure to diacetyl produces morphological liver alterations according to animal studies. Another 2016 review surfaced concerns that e-liquid additives might lead to diseases such as popcorn lung. The irritants butyl acetate, diethyl carbonate, benzoic acid, quinoline, bis(2-ethylhexyl) phthalate, and 2,6-dimethyl phenol were present as undeclared ingredients in the e-liquid. Aldehydes may cause harm. Another 2015 study reported that "dripping", where the e-liquid is dripped directly onto the atomizer, can create carbonyls. The amount of formaldehyde expected to be inhaled by the user is disputed. A 2014 review concluded that e-cigarettes have a pharmacokinetic nicotine profile closer to nicotine replacement products than to traditional cigarettes. Another 2014 review concluded that serum cotinine levels were comparable to traditional cigarettes, but varied by usage pattern and device. In 2018 the National Academies of Sciences, Engineering, and Medicine reported that the degree of dependence is less for e-cigarettes than traditional cigarettes. The aerosol is made-up of liquid sub-micron particles of condensed vapor; thus, the users of these devices are rather "aerosolizing." lead, Heavy metals are correlated with serious health issues. A 2016 review concluded that metals reported in vapor may induce cell damage and initiate inflammatory cytokine such as in human lung fibroblasts. A 2017 review linked cadmium to low sperm density. First-generation devices Compared to traditional cigarettes, older devices typically produced much lower blood nicotine levels, Tank/adjustable devices Tank or adjustable e-cigarettes, as well as concentrated nicotine liquids, may deliver nicotine at levels similar to traditional cigarettes. As of 2017 fourth-generation devices had not been heavily researched. How do e-cigarettes affect the brain? The nicotine in e-liquids readily absorbs into the bloodstream when a person uses an e-cigarette. Youth concerns Commissioner Scott Gottlieb announced on 28 July 2017 a comprehensive regulatory plan for tobacco and nicotine regulation that will serve as a multi-year roadmap to better protect youth and significantly reduce tobacco-related disease and death, including pursuing lowering nicotine in regular cigarettes to a minimally or non-addictive level. Exposure to e-cigarette components in a susceptible time period of brain development could induce persistent behavioral changes. One study reported increased irritability among infants in those exposed to e-cigarettes or smoking. A 2022 study recommended quitting smoking altogether through smoking cessation therapy rather than turning to e-cigarettes as an alternative. The U.S. Preventive Services Task Force (USPSTF) recommended that pregnant women adopt behavioral interventions for quitting. Ecigs vaped by pregnant women may increase copd and asthma risk in offspring. == See also ==