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The risks of electronic cigarette use are uncertain. This is due to there being little data regarding their health effects and to the variability of vaporizers and variability in liquid ingredients and in their concentration and quality, and thus variability of the contents of vapor delivered to the user. The limited evidence suggests that e-cigarettes are probably safer than traditional cigarettes. They appear to be similar in toxicity to other nicotine replacement products, but there is not enough data to draw conclusions. The evidence suggests that the US Food and Drug Administration (FDA) accepted products such as a nicotine inhaler may be a safer way to give nicotine than e-cigarettes. A July 2014 World Health Organization (WHO) report cautioned about potential risks of using electronic cigarettes. The report concluded that "the existing evidence shows that ENDS aerosol is not merely "water vapour" as is often claimed in the marketing for these products. ENDS use poses serious threats to adolescents and fetuses." A 2014 systematic review concluded that the risks of e-cigarettes have been exaggerated by health authorities and stated that while there may be some residual risk it is likely trivial compared to continuing to smoke. As of 2014, e-cigarettes cannot be regarded as harmless or safe until additional data is available on the topic. No long-term studies have shown that e-cigarettes are a "healthier alternative" to traditional cigarettes.

The distribution on the amount of nicotine inhaled by the user is not clear. The risk is probably low from the inhalation of propylene glycol and glycerol. When heated at hotter temperatures glycerol may generate harmful acrolein. There are no studies in respect to the short- and long-term effects of the inhalation for aromatic substances. The levels of chemical constituents in the vapor were found to be 1 to 2 orders of magnitude smaller than in cigarette smoke but greater compared to a nicotine inhaler. The long-term health impacts of e-cigarette use are unknown. There is limited information available on the environmental issues in connection with the production, the usage, and the disposing of e-cigarettes. Less serious adverse effects from e-cigarette use include throat and mouth inflammation, vomiting, nausea, and cough. Long-term studies regarding the effects of e-cigarettes after chronic exposure are unavailable.

The aerosol emitted from an e-cigarette is commonly but inaccurately called vapor. The particle size distribution of particles emitted by e-cigarettes are like traditional cigarettes, with the majority of particles in the ultrafine range (modes, ≈100–200 nm). Exhaled vapor consists of nicotine and some other particles, primarily consisting of flavors, aroma transporters, glycerol and propylene glycol. A 2014 WHO report stated passive exposure was as a concern, indicating that current evidence is insufficient to determine whether the levels of exhaled vapor are safe to involuntarily exposed bystanders. The report concluded that the aerosol emissions are likely to increase the risk of disease to nearby bystanders, especially from those e-cigarettes which produce toxicant levels close to those emitted by certain cigarettes. E-cigarette vapor has notably fewer toxicants than cigarette smoke and is likely to pose less harm to users or bystanders. There is insufficient data to determine the impact on public health from e-cigarettes. It is recommended that e-cigarettes should be adequately regulated for consumer safety.

Toxicology

A preliminary analysis of e-cigarette cartridges by the US Food and Drug Administration (FDA) in 2009 identified that some contain tobacco-specific nitrosamines (TSNAs), known cancer-causing agents, namely anabasine, myosmine, and β-nicotyrine. These were detected in a majority of the samples at levels similar to a licensed nicotine inhaler. The FDA's analysis also detected diethylene glycol, which is poisonous, in a single cartridge manufactured by Smoking Everywhere and nicotine in one cartridge claimed to be nicotine-free. This prompted the FDA to warn that e-cigarettes may present a health risk. 15 other studies have failed to find diethylene glycol in e-cigarettes. The UK National Health Service noted that the toxic chemicals found by the FDA were at levels one-thousandth that of cigarette smoke, and that while there is no certainty that these small traces are harmless, initial test results are reassuring. Further concerns were raised over inconsistent amounts of nicotine delivered when drawing on the device. They appear to be similar in toxicity to licensed nicotine replacement products, but there is not enough data to draw firm conclusions; one 2014 review found higher levels of carcinogens and toxins than in an FDA-approved nicotine inhaler, suggesting that FDA-approved devices may deliver nicotine more safely.

Serum nicotine levels identified are inharmonious and rely upon the user and the device. There was inconsistent labeling of the actual nicotine content on e-liquid cartridges from some brands. Some nicotine has been found in ‘no nicotine' liquids. Due to nicotine content inconstancy, it is recommended that e-cigarette companies develop quality standards with respect to nicotine content. There are safety issues with the nicotine exposure from e-cigarettes, which has the possibility of causing addiction and other adverse effects. Serum cotinine levels are comparable to that of traditional cigarettes. The risk is probably low from the inhalation of propylene glycol and glycerol. Some research states that propylene glycol emissions may cause respiratory irritation and raise the likelihood to develop asthma. E-cigarettes companies use purified water and glycerin instead of propylene glycol for aerosol production to lesson the risks. When heated at hotter temperatures glycerol may generate harmful acrolein. Some e-cigarette products had acrolein identified in the aerosol. If exposure of aerosols to propylene glycol and glycerin rises to levels that one would consider the exposure in association with a workplace setting, it would be sensible to investigate the health of exposed persons. The essential propylene glycol and/or glycerol mixture may consist of natural or artificial substances to provide it flavor. Some of these substances are regarded as toxic and a number of them resemble known carcinogens. Although the majority of aromatic substances that mimic tobacco and others using generally inaccurate terms such as ‘vegetable flavoring' are approved for human use, there are no studies in respect to the short- and long-term effects of the inhalation of these substances. Some artificial flavors have been demonstrated as being cytotoxic.

A 2014 review found "Various chemical substances and ultrafine particles known to be toxic, carcinogenic and/or to cause respiratory and heart distress have been identified in e-cigarette aerosols, cartridges, refill liquids and environmental emissions." Many toxic chemical compounds have been produced from e-cigarettes, especially carbonyl compounds like formaldehyde, acetaldehyde, acrolein, and glyoxal, which are frequently identified in e-cigarette aerosols. These materials may cause harmful health effects; though, in the majority of cases, the amounts inhaled are less than those in traditional cigarettes. The toxicity of e-cigarettes and e-liquid can vary greatly, as there is potential differences in construction and materials in the delivery device, kind and origin of ingredients in the e-liquid, and the use or non-use of good manufacturing practices and quality control approaches. While there is variability in the ingredients and concentrations of ingredients in e-cigarette liquids, tobacco smoke contains thousands of chemicals, most of which are not understood and many of which are known to be harmful. The levels of chemical constituents in the vapor were found to be 1 to 2 orders of magnitude smaller than in cigarette smoke but greater compared to a nicotine inhaler. The Centers for Disease Control and Prevention (CDC) stated the possible negative impact between nicotine and brain development in youth is a concern. The short-term toxicity of e-cigarette use appears to be low, with the exception for some people with reactive airways. Long-term toxicity and cancer risk will depend on exposure to contaminants and the low level of carcinogens in the e-liquid; research and data is currently limited, and potential effects are unknown.

A 2013 review found after using a single e-cigarette there was an instant increase in airways resistance and concluded that they can do harm to the respiratory system. The risks, especially to the lungs, are not fully understood and are of concern to public health authorities. A 2014 review found that e-cigarettes used in the short-term on specified cardiovascular and respiratory functional results have demonstrated that even though some minor harmful effects of vaping are documented, these are appreciably milder in comparison to traditional cigarettes. When used in the short-term, an e-cigarette results in a rise of respiratory resistance comparatively to traditional cigarettes. The long-term effects regarding respiratory flow resistance are unknown. E-cigarette use can be associated with a substantial dispersion of nicotine, thus generating a plasma nicotine concentration which can be comparable to that of traditional cigarettes. This is due to the minute nicotine particles in the vapor, which permit quick delivery into the bloodstream. This could increase the risk of cardiac arrhythmias and hypertension, which could affect some users, particularly those with atherosclerosis or other cardiovascular risk factors, to developing a significant risk of acute coronary syndrome. The limited evidence suggests that e-cigarettes produce less short-term effects on lung function than traditional cigarettes. Like cancer risk, there is no literature outlining the long-term lung function or cardiovascular consequences. A 2014 review found 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. The affect on population health from e-cigarettes is unknown.

Environmental impact

No studies have been conducted into any environmental issues connected to the production, usage, and disposal of e-cigarettes or the nicotine they contain. Some e-cigarette brands state their products are ‘eco-friendly’ or ‘green’. It is unclear how many traditional cigarettes are comparable to one e-cigarette when looking at the cost of manufacturing them. Some brands have began recycling services for their e-cigarette cartridges and batteries but the prevalence of recycling is not known.

Adverse effects

Health effects

E-cigarettes use lithium batteries most of the time; improper use may result in accidents. Rare major injuries have occurred from battery malfunctions such as explosions and fires. The explosions resulted either through extended charging and use of unsuitable chargers or as a result of design flaws. It has been recommended that manufacturing quality standards are imposed to reduce or prevent such accidents. Use-related concerns with e-liquids involve leaks or spills and contact with contaminants in the e-liquid.

Less serious adverse effects including throat and mouth inflammation, vomiting, nausea, and cough have resulted from e-cigarette use. Adverse effect are mostly associated with a short term of use, and their frequency was significantly lower after 52 weeks of use. Long-term studies regarding the effects of e-cigarettes after chronic exposure are unavailable. Many of the observed negative effects from e-cigarette use concerning the nervous system and the sensory system are probably related to nicotine overdose or withdrawal. In youth, e-cigarette use risks involve accidental nicotine exposure and possible choking dangers. In pediatric patients, accidental exposures include ingesting of e-liquids and inhaling of e-cigarette vapor. The US Food and Drug Administration Center for Tobacco Products reported between 2008 and the beginning of 2012, 47 cases of adverse effects associated with e-cigarettes, of which eight were considered serious. A causal relationship between e-cigarettes and the reported adverse effects was not established with the exception of two severe outcomes in the United States: a death when an infant choked on the cartridges and burns when one blew up.

In the United States the number of calls to poison control centers related to electronic cigarettes have increased between 2010 and 2014, such that they now represent 42% of reported cases due to either cigarettes and e-cigarettes up from 0.3%. These calls were in connection to both adults and children. E-cigarettes were associated with fewer adverse effects than nicotine patches. Calls to U.S. poison control centers related to e-cigarette exposures involved inhalations, eye exposures, skin exposures, and ingestion, in both adults and young children. The California Poison Control System reported 35 cases of e-cigarette contact from 2010 to 2012,. 14 were in children and 25 were from accidental contact. The majority of adverse effects reported were nausea, vomiting, dizziness and oral irritation.

Aerosol

First hand exposure

E-cigarettes produce an aerosol of sub-micron liquid droplets, although this is commonly called "vapour". This aerosol resembles cigarette smoke and is delivered to the user through a mouthpiece, after which the remaining aerosol is exhaled into the environment." E-cigarette vapor mostly consist of propylene glycol, glycerol, water, flavorings, nicotine, and some other chemicals.

Ultrafine Particles

Fine particles can be chemically intricate; it is not known to what extent any health effects depend on toxicity and size. Emissions from electronic cigarettes are not comparable to environmental pollution or cigarette smoke as their nature and chemical composition are completely different. The particles are also larger, with the mean size being 600nm in inhaled aerosol and 300nm in exhaled. Electronic cigarettes release a lower level of particles than cigarettes by a factor of between 6 and 880 times.

Some e-cigarette liquids and emissions contain the heavy metals nickel, tin, and chromium. Nanoparticles of these metals may be deposited in the lung's alveolar sacs, potentially leading to local respiratory toxicity or entering the bloodstream. However levels of these metals are typically 10-50 times lower than what is permitted in inhalable medications and a 2014 study concluded that this level of metal contamination does not support health concerns.

Second hand exposure

Since e-cigarettes do not burn (or contain) tobacco, no side-stream smoke or any cigarette smoke is produced. Only what is exhaled by electronic cigarettes users enters the surrounding air. E-cigarettes used in indoor environments can put at risk nonsmokers to elevated levels of nicotine and aerosol emissions. A 2014 review of limited data concluded this vapor can cause indoor air pollution and is not just "water vapor" as is frequently stated in the advertising of e-cigarettes. Exhaled vapor consists of nicotine and some other particles, primarily consisting of flavors, aroma transporters, glycerol and propylene glycol. Bystanders are exposed to these particles from exhaled e-cigarette vapor. A mixture of harmful substances, particularly nicotine, ultrafine particles, and volatile organic compounds can be exhaled into the air. The dense vapor consists of liquid sub-micron droplets. The liquid particles condenses into a viewable fog. The vapor is in the air for a short time, with a half-life of about 10 seconds; traditional cigarette smoke is in the air 100 times longer. This is because of fast revaporization at room temperature. Some of the few studies examining the effects on health shown that being exposed to e-cigarette vapor may produce biological effects. Since e-cigarettes have not been widely used long enough for evaluation, the long-term health effects from the second-hand vapor are not known.

As of 2013, the only clinical study currently published evaluating the respiratory effects of passive vaping found no adverse effects were detected. A 2014 review found it is safe to infer that their effects on bystanders are minimal in comparison to traditional cigarettes. A 2014 WHO report stated passive exposure was as a concern, indicating that current evidence is insufficient to determine whether the levels of exhaled vapor are safe to involuntarily exposed bystanders. The report concluded that the aerosol emissions are likely to increase the risk of disease to nearby bystanders, especially from those e-cigarettes which produce toxicant levels close to those emitted by certain cigarettes. E-cigarette vapor has notably fewer toxicants than cigarette smoke and is likely to pose less harm to users or bystanders.

Nonsmokers exposed to e-cigarette aerosol produced by a machine and pumped into a room were found to have detectable levels of the nicotine metabolite cotinine in their blood. The same study stated that 80% of nicotine is normally absorbed by the user, so these results may be higher than in actual second hand exposure. There are concerns about pregnant women exposed to e-cigarette vapor through direct use or via exhaled vapor; As of 2014 potential effects are unknown and research is ongoing.

There is insufficient data to determine the impact on public health from e-cigarettes. A white paper published in 2014 by the American Industrial Hygiene Association concluded e-cigarettes emit airborne contaminants that may be inhaled by the user and those nearby. Due to this possible risk, they urged restriction of their use indoors, similar to smoking bans, until research has shown the aerosol does not significantly harm others in the area. A 2014 review indicated that the levels of inhaled contaminants from the e-cigarette vapor are not of significant health concern for human exposures by the standards used in workplaces to ensure safety.

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External links

• Media related to Electronic cigarettes at Wikimedia Commons

• Cigarette types
• Technology
• Chinese inventions
• Smoking cessation
• 2003 introductions