June 23, 2021

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Can e-cigarette cause cancer because it still contains carcinogens?

15 min read
Can e-cigarette cause cancer because it still contains carcinogens?

Can e-cigarette cause cancer because it still contains carcinogens?  Ten important questions about e-cigarette.

Can e-cigarette cause cancer because it still contains carcinogens? What are the hazards of formaldehyde, acetaldehyde, acrolein, and o-methylbenzaldehyde detected in electronic cigarettes to the human body? Compared with traditional cigarettes, which is more harmful?

Many studies points out the health hazards of e-cigarettes in detail from the harmful substances of e-cigarette liquid and aerosols, and young people who are more likely to be contaminated with cigarettes after using e-cigarettes, and are accompanied by relevant research certificates. Are e-cigarettes harmful? Let’s count the addiction, toxic and harmful substances, and difficulty of withdrawal from e-cigarettes and traditional cigarettes.



Q1: What are the hazards of formaldehyde, acetaldehyde, acrolein, and o-methylbenzaldehyde detected in e-cigarettes to the human body? Compared with traditional cigarettes, which is more harmful?

Electronic cigarettes heat and atomize e-liquid (a mixture of vegetable glycerin, propylene glycol, nicotine and flavoring agents) under electric heating. Volatile carbonyl compounds are produced in the smoke, which is one of the main harmful components. The main forms of carbonyl compounds include formaldehyde, acetaldehyde, acrolein, o-methylbenzaldehyde and glyoxal. These are known carcinogens with potential dangers and can have various effects on the health of users.

Formaldehyde is extremely active and easily soluble in water. It has been listed by the International Agency for Research on Cancer (IARC) as a Class I carcinogen related to sinus cancer and nasopharyngeal cancer, that is, “known human carcinogens.” 

Acetaldehyde is also a highly mutagenic and active carcinogen, and is classified as a IIB carcinogen by IARC. The harmfulness of acetaldehyde has already been proven because it is also produced during drinking. We know that after drinking alcohol (ethanol) will be catalyzed by alcohol dehydrogenase (ADH) to produce acetaldehyde, and acetaldehyde will further form acetic acid under the action of acetaldehyde dehydrogenase (ALDH).

However, Asians generally have some genetic mutations, which can lead to increased alcohol dehydrogenase (ADH) activity or decreased acetaldehyde dehydrogenase (ALDH) activity, which leads to a large accumulation of acetaldehyde in the human body, causing physical discomfort -Dizziness, blushing, reduced mobility and reflexes-that is, the performance of drunkenness.

A study of more than 70,000 Asians found that people who carry a genetic variant that can reduce the activity of acetaldehyde dehydrogenase (ALDH) have a strong drunken response, and they drink significantly less alcohol than others overall. Because people drink a lot of alcohol and have a high concentration of acetaldehyde in their body, their cancer risk increases by 32%.

The 160,000 study published in the international authoritative medical journal “The Lancet” found that for men, drinking two 40-degree liquor or two cans of beer a day increases the risk of ischemic stroke by 27%, and hemorrhagic stroke (hemorrhage) Sexual stroke) increased by 58%! It also increases the diastolic blood pressure by 4.3 mmHg. People who both smoke and drink have a higher risk of cancer and cardiovascular disease.

Acrolein can irritate the nasal cavity and damage the lung mucosa. O-methylbenzaldehyde is a toxic and strong oxidant, which is strongly irritating to eyes, skin and mucous membranes. Inhalation strongly stimulates the respiratory tract. Glyoxal and methylglyoxal are mutagenic, and can react with human DNA, leading to breakage or mutation, and induce the formation of cancer cells. The behavior of formaldehyde releasing agents (hemiacetal) in the respiratory tract is currently unclear.

The content of carbonyl compounds in e-cigarettes varies significantly between different brands, and even between different samples of the same product. In most cases, the levels of carbonyl compounds detected in e-cigarettes are lower than traditional cigarette smoke, but very high levels of formaldehyde have also been reported in e-cigarette aerosols. For example, in a 2014 study by Kosmider et al., 13 aerosol samples produced by Polish e-cigarettes were tested, and formaldehyde and acetaldehyde were detected in 8 samples. At lower voltages, the content of formaldehyde and acetaldehyde in e-cigarette aerosols are on average 13 times and 807 times lower than those in traditional cigarette smoke, respectively.

Another study conducted by Hutzler et al. measured formaldehyde in e-cigarette aerosols. The study found that the exposure of e-cigarette users to formaldehyde is comparable to that of traditional cigarettes. They measured the formaldehyde content in the final fraction of every 10 inhalations to be 20-50µg, which is equivalent to the exposure of a traditional cigarette. Blair et al. measured and compared the acrolein in e-cigarettes and traditional cigarette smoke aerosols, and found that the acrolein content of 5 e-cigarettes was 0.290±0.018μg, while the acrolein content of 9 traditional cigarettes was 2.61±0.16μg.

The relative standard deviations of all average measurements have a wide range, which indicates that there are inconsistencies between products in terms of the release of these chemicals. Researcher Tayyarah tested 55 harmful and potentially harmful components in e-cigarette aerosols and quantified three carbonyl groups (acrolein, acetaldehyde, and propionaldehyde), the levels of which were 86 to 544 times lower than that of traditional cigarette smoke.



Q2: Are cigarette tar and nicotine in traditional cigarettes also contained in e-cigarettes? What are the hazards to the human body? Compared with traditional cigarettes, which is more harmful?

Electronic cigarettes do not produce tar and carbon monoxide, thus reducing the harm of tar and carbon monoxide to the human body.

However, e-cigarettes contain an addictive substance-nicotine. Nicotine is a nicotinic acetylcholine receptor agonist, which can stimulate the protein receptors in tracheal epithelial cells, immune cells, and vascular endothelial cells-nicotinic acetylcholine receptors. Genetic studies have found that nicotinic acetylcholine receptors are related to lung cancer.

This receptor can regulate cell proliferation and inhibit cell apoptosis-uncontrolled cell proliferation is a sign of cancer. In genome-wide association studies, genes related to nicotinic acetylcholine receptors are associated with the risk of lung cancer. In addition, differences in the expression profile of nicotinic acetylcholine receptors between non-smokers and non-small cell lung cancer smokers were also observed.

Whether the chronic activation of nicotine in e-cigarettes on nicotinic acetylcholine receptors can lead to lung cancer is unclear, but the role of the receptors in non-small cell lung cancer by changing cell proliferation and apoptosis resistance has been reported.

Studies have found that nicotine causes vascular endothelial dysfunction by increasing the leakage of vascular endothelium. In addition, exposure to nicotine (rather than propylene glycol/vegetable glycerin) can increase arterial stiffness and adversely affect microcirculation, indicating that the nicotine released by e-cigarettes may be a risk factor for cardiovascular disease.Exposure to nicotine in e-cigarettes may affect any organ that expresses nicotinic acetylcholine receptors.

Therefore, the use of e-cigarettes may affect the inflammation of the respiratory tract and increase the risk of infection, chronic obstructive pulmonary disease or lung cancer. Except for nicotine, under normal use conditions, the exposure to potentially toxic substances in e-cigarettes is lower than that of combustible tobacco cigarettes, but it cannot be concluded that its health hazards are less than traditional cigarettes.



Q3: What are the hazards of e-cigarette aerosol? Compared with the second-hand smoke of traditional cigarettes, which is more harmful than the second-hand smoke of electronic cigarettes?

The aerosol of e-cigarettes is not harmless “water vapor”. The smoke that users inhale and exhale from e-cigarette devices contains harmful and potentially harmful substances, including nicotine, ultrafine particles that can be inhaled deep in the lungs, and fragrances (such as diacetyl, a type of Chemical substances), volatile organic compounds, carcinogens, heavy metals (such as nickel, tin and lead), etc. Therefore, the “second-hand smoke” of electronic cigarettes is still harmful.

For this reason, the United Kingdom and other European countries have also incorporated electronic cigarettes into laws, prohibiting the use of electronic cigarettes in public places and enclosed spaces (often understood as “any covered structure”). However, compared with the “second-hand smoke” of traditional cigarettes, the “second-hand smoke” of electronic cigarettes does not have high concentrations of tar and carbon monoxide, which are one of the important risk factors for cardiovascular disease and cancer. Some current evidences believe that it is less harmful than traditional cigarettes. Smoke, but still harmful. There are many complex chemical substances produced by electronic cigarettes, and electronic cigarettes have been invented and used for a short period of time. Whether the long-term health hazards of “second-hand smoke” are different from traditional cigarettes has not yet been proved, and more research is urgently needed to follow up and confirm.



Q4: Are the flavors added to e-cigarettes harmful to humans?

The e-cigarette’s e-liquid contains a variety of flavor additives, which can be divided into aldehydes, alcohols, pyrazines, ketones, and sweeteners including ethyl maltol according to the types of chemical elements (see below).

  • Vanillin:  vanilla
  • Benzaldehyde: Fruit
  • Cinnamaldehyde:  Cinnamon
  • Damascus:  Tobacco
  • Benzyl alcohol:  Flowers
  • Linalool:  Flowers
  • Farnesol: Apple
  • Menthol:  mint
  • Pyrazine:  coffee, chocolate
  • Menthone:  Peppermint


These additives with different flavors are combined with other chemical substances to produce a wide range of flavored e-cigarette liquids on the market. Some flavor additives are food additives and cosmetic fragrances. However, the safety of their inhalation into the lungs in the form of e-cigarettes is unclear. Although occupational exposure to these additives is regulated, their concentration in e-cigarettes is not regulated. This is a big safety hazard, because formaldehyde flavoring agents are harmful in high concentrations. The concentration of flavoring agents inhaled into the lungs through e-cigarettes, like nicotine, is unclear.

An in vitro study evaluated about 150 e-liquids and found that the amount of flavors in e-liquids was positively correlated with their in vitro toxicity. The study also found that the concentrations of vanillin and cinnamaldehyde in different e-liquids were related to overall toxicity. The concentration of cinnamaldehyde in the smoke liquid can exceed 1m (mole), and the cinnamaldehyde-flavored electronic cigarette aerosol can cause cytotoxicity and cilia dysfunction and inflammation of the epithelial cells in the body.

People are more concerned about the butter-flavored diacetyl in the smoke liquid because it is known to have pulmonary toxicity and the tendency to cause obstructive bronchiolitis. It is worth noting that the aldehyde seasoning and propylene glycol/vegetable glycerin can react chemically within a few hours after mixing to form acetal compounds. These compounds are stable in the water environment at physiological pH, but as aerosols, they can activate stimulus receptors. Therefore, e-liquid is much more complicated than originally thought, and it is not chemically stable, and can form compounds with new respiratory toxicological effects.



Q5: What harmful substances in e-cigarettes are not found in traditional cigarettes? What are the harms of these substances to the human body?

There is a lot of research evidence that, in addition to nicotine, most e-cigarette products contain and release many potentially toxic substances. Moreover, depending on the characteristics of the product (including the characteristics of the device and the e-cigarette liquid) and the operation mode of the device, in addition to nicotine, the amount and characteristics of potentially toxic substances emitted by e-cigarettes vary greatly.

A large amount of evidence shows that the aerosol of e-cigarettes contains metals. The source of these metals may be the metal coil used to heat the e-liquid, other parts of the e-cigarette device, or the e-liquid. Product characteristics and usage patterns may cause differences between the actual metal content in the e-cigarette aerosol and the measured metal concentration. There is limited evidence that the metal content of e-cigarette aerosols may be higher than that of metals other than cadmium in traditional cigarettes.

The basic ingredient of e-cigarette liquid is propylene glycol/vegetable glycerin. Propylene glycol is a common chemical used in the production of polyester and deicing/antifreeze, and it is also a common food additive. It usually forms aerosols in e-cigarettes and is inhaled into the human body.

And vegetable glycerin (VG) is glycerin extracted from plants. Like propylene glycol, it is used as a fusion agent in e-cigarette liquid. Although in the food industry, both are considered safe as food additives, the inhalation safety is not so. Short-term occupational exposure to propylene glycol can cause irritation with slight or no objective effects on lung function, indicating that propylene glycol may be a sensory irritant. In cell and animal models, propylene glycol can cause abnormal excitement in sensory nerves and participate in the promotion of asthma inflammation and airway hyperresponsiveness. Propylene glycol/plant glycerin increases the expression of mucin in primary airway epithelial cells.

Both propylene glycol and plant glycerin are fat-soluble substances, which can enter the cell through the cell channel, or can play a role in the cell. The cell membrane is also mainly composed of a large amount of lipids. Plant glycerol can enter the cell membrane and affect the biological membrane including the cell membrane. Studies have found that propylene glycol and vegetable glycerin reduce the fluidity of airway epithelial cell membranes. The decrease in membrane fluidity may affect endocytosis (including phagocytosis, a special form of endocytosis), exocytosis, and plasma membrane protein-protein interactions. “Dosage and the way to produce toxins” is the basic principle of toxicology, and it is unscientific to talk about toxicity without dosage. Long-term inhalation of e-cigarettes can lead to high-dose inhalation of propylene glycol/vegetable glycerin, which adds to the harm of inhaled nicotine.

Many chemical substances other than nicotine have been found in the liquids and aerosols produced by e-cigarettes, and contain hundreds of unspecified and unregulated compounds that are not found in tobacco. Compounds not listed on the label are also identified in the e-liquid. As mentioned above, several harmful compounds found in liquids and heated aerosols produced by electronic cigarettes, including formaldehyde, acetaldehyde and acrolein, are known carcinogens. What is more worrying is that the added fragrance additives are considered safe, but their sensitization, toxicity or irritant effects have not been extensively tested.

More and more studies have detected metals in e-cigarette liquid and aerosol samples produced by e-cigarette devices. Some key metals include chromium, nickel, lead, manganese, aluminum, tin and iron. Metal exposure can come from several parts of the device, including metal coils, a complex alloy that heats e-liquid to produce aerosols that are inhaled by users. Other parts of the device, such as joints and wires, can also play a role. For example, Kanthal, an alloy often used in e-cigarettes, contains aluminum, chromium, and iron. Other common alloys are Ni-200 (made of nickel) and nic chromium (made of chromium and nickel). In addition, tin and other metals were also found at the joints.

E-liquid may also contain metals in different concentrations. For example, some e-cigarette liquid solutions contain arsenic.



Q6. Overall, compared to traditional cigarettes, is e-cigarette smoking more harmful? Is it relatively safer?

Most of the adverse effects of smoking (lung cancer, chronic obstructive pulmonary disease) take decades to manifest. Our adverse effects on traditional tobacco are the scientific conclusion that “smoking is harmful to health” after several generations of research. However, many specific harms of traditional tobacco to the human body are still in the process of more in-depth research. The long-term effects of e-cigarettes on chronic diseases such as cardiovascular and cancer, mental illnesses such as depression, addiction, and schizophrenia, and how people use e-cigarettes most effectively to quit smoking remains unclear.

A study published in November 2019 by the University of Dundee, funded by the British Heart Foundation, showed that e-cigarettes may be less harmful to blood vessels than smoking. Within a month of switching from tobacco to e-cigarettes, blood vessel health indicators including blood pressure and arteriosclerosis began to improve. The study surveyed 114 people who had smoked traditional cigarettes for at least two years and at least 15 cigarettes a day. However, the study was carried out in a relatively small number of people, and it could not prove that e-cigarettes are completely safe. E-cigarettes may be a useful tool to help people quit smoking, but non-smokers should never start smoking e-cigarettes.



Q7. Will electronic cigarettes become addictive? What is the principle of addiction? Compared with traditional cigarettes, who is more likely to become addicted?

Electronic cigarettes are addictive. Electronic cigarettes, like ordinary cigarettes, contain nicotine. Studies have shown that nicotine can be as addictive as heroin and cocaine. Many smokers get more nicotine from e-cigarettes than they get from tobacco products—consumers can buy enhanced cigarette packs that contain higher concentrations of nicotine, or they can increase the voltage of e-cigarettes to get more Nicotine stimulation. When nicotine addiction is not satisfied, withdrawal symptoms occur.

In addition to the addictive nature of nicotine, e-cigarettes, which are popular as fashion products, also attract consumers on a psychological level. Compared with other traditional tobacco products, young people are more likely to be attracted to e-cigarettes. In 2015, the Secretary of the US Department of Health reported that the number of high school students using e-cigarettes has increased by 9 times, and 40% of young e-cigarettes have never smoked traditional tobacco. There may be four reasons why e-cigarettes are attractive to young people. First, out of a curiosity about new things, they began to try e-cigarettes; second, many teenagers believe that e-cigarettes are less harmful than smoking; third, the cost per use of e-cigarettes is lower than that of traditional cigarettes; fourth, compared Compared with traditional cigarettes with no odor, e-cigarettes often add flavorings such as apples and watermelons to attract young users; finally, e-cigarettes reduce the stigma of smoking and even increase the “fashion”.
Many people who did not smoke before, especially young people, have started to get infected with e-cigarettes
The habit of smoking increases the possibility that people will smoke traditional tobacco products in the future. The combination of these physical, psychological and social factors may make it more difficult to quit e-cigarettes.



Q8: Can e-cigarettes be used as a tool for smoking cessation?

A review of studies has shown that e-cigarettes containing nicotine can help people quit traditional cigarettes for 6 months or more. It may be better than some other smoking cessation methods (such as nicotine replacement therapy and the use of nicotine-free e-cigarettes).

Traditional methods of quitting smoking include:

· Nicotine replacement therapy, such as patches or chewing gum;

· Varenklin (a drug that helps people quit smoking);

·Nicotine-free electronic cigarettes;

·Behavioral support, such as advice or consultation;

· Without any support.

A combination of studies in the United States (24 items), the United Kingdom (9 items) and Italy (7 items) shows:

·Compared with using nicotine replacement therapy or not using nicotine e-cigarettes, there may be more people who use nicotine e-cigarettes to quit smoking for no less than 6 months;

·Nicotine e-cigarettes may be more helpful in quitting smoking than no support or pure behavioral support;

· 10 or 11 out of every 100 people who use e-cigarettes to quit smoking successfully quit smoking; in contrast, only 6 out of 100 people who used nicotine replacement therapy or nicotine-free e-cigarettes successfully quit smoking without any support or only Only 4 out of 100 people supported by behavior successfully quit smoking.

Current research is still uncertain whether there is a difference between the use of nicotine e-cigarettes and the use of nicotine replacement therapy (without support or only behavioral support). At present, e-cigarettes containing nicotine may help more people quit smoking than nicotine replacement therapy or nicotine-free e-cigarettes. However, further research and evidence may change these results. Even if you use e-cigarettes to quit smoking, you need some supportive help.

Although e-cigarettes seem to be a tool to help quit smoking, in the United States, e-cigarettes have not yet been approved by the U.S. Food and Drug Administration (FDA) as a smoking cessation device. A recent study found that most people who want to use e-cigarettes to quit the nicotine habit will eventually continue to smoke traditional cigarettes and e-cigarettes. In view of the outbreak of related lung injuries caused by the use of e-cigarette products, the Centers for Disease Control and Prevention (CDC) recommends that adults who use e-cigarettes to quit smoking weigh the risks and benefits, and consider using other FDA-approved smoking cessation programs.



Q9: After smoking e-cigarettes, why is it easier to smoke traditional cigarettes? Is there a scientific basis? Or is it more of a psychological effect?

For many young people, the first exposure to nicotine is through e-cigarette smoking. Nicotine is a known addictive drug. E-cigarette addiction can easily become an incentive to smoke traditional cigarettes. An e-cigarette survey conducted by the Zhejiang Provincial Center for Disease Control and Prevention in 2017 found that among the 24,000 middle school students, 70% of the students had knowledge of e-cigarettes, 1,214 (5.3%) were traditional smokers, and some 492 (2.1%) people smoke e-cigarettes, and nearly half of them have smoked traditional cigarettes.

Although this does not directly prove that e-cigarettes will lead to a switch to traditional cigarettes, it shows that young people who smoke e-cigarettes are likely to smoke traditional cigarettes. Judging from the evidence of smoking cessation, most people who use e-cigarettes to quit the nicotine habit will eventually continue to smoke traditional cigarettes + e-cigarettes. 



Q10: Which is easier to quit e-cigarettes or traditional cigarettes? why?

As mentioned above, the nicotine of e-cigarettes is easier to obtain or even has a higher concentration, and it is more likely to be addictive.  The circulation and acquisition of e-cigarettes It is easy, coupled with insufficient publicity on its harmful effects, and low social support for quitting e-cigarettes, which increases the difficulty of quitting e-cigarettes. At present, there is no conclusive evidence and research to compare the difficulty of quitting e-cigarettes and traditional cigarettes.

Can e-cigarette cause cancer because it still contains carcinogens?

Richard Doll (Image source: Department of Population Health, University of Oxford)

Conclusion: In the building of the Department of Human Health, University of Oxford, the British “Tobacco Carcinogen Discoverer” and “Father of Epidemiology” Richard Doll (Richard Doll)’s portraits read “Death in old” on the next nameplate. age is inevitable, but death before old age is not”. The millions of lives killed by smoking every year can be avoided.



(source:internet, reference only)

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