Introduction. The popularity of electronic cigarettes spread faster than doctors had time to assess their danger. An interesting fact is that the first electronic cigarettes were invented and patented by Chinese pharmacist Hong Lik, who himself smoked a lot for a long time. After his father’s death due to lung cancer due to smoking, Hong Lik decided to quit smoking immediately and come up with a device that would help with this. In 2003, he designed the first electronic cigarette, which was based on the principle of a steam generator. The design he created is still used in their production.
Most are unaware of the harm of electronic cigarettes, believing that they are not dangerous, unlike conventional cigarettes, calling them almost harmless. But is it true? It is necessary to intervene and deal with this issue, because studies show that use causes diseases of the teeth and gums.
Materials and methods. Analysis of studies proving the harmful effects of e-cigarettes during prolonged smoking.Study of the harmful effects of electronic cigarettes on the development of a number of pathologies, including diseases of the oral mucosa.
Results. The smoking liquid is a mixture of propylene glycol, glycerin, flavorings and, optionally, nicotine. It became known that mutagenic substances, in particular acrolein and formaldehyde, are formed during vaping. The heating element also releases harmful substances with steam, such as propylene oxide, glycidol, heavy metals and silicate particles, which are potential carcinogens. 
According to research, the aerosol interacts with harmful bacteria that are on the surface of the teeth and lead to caries, making them more resistant. Reducing the amount of saliva when smoking e-cigarettes also helps these bacteria: the environment becomes more nutritious for them, hygiene becomes more difficult, the pellicle (a structural element of the surface layer of enamel) becomes thinner.
Scientists of the All-Russian Research Institute of Tobacco and Tobacco Products reported on the results of a detailed study of electronic cigarettes, revealed that they contain «moderately dangerous substances» in huge concentrations. 
Also the Department of Food and Drug Control analyzed 19 different electronic cigarettes, and also came to the conclusion that they are not so harmless. Scientists have found substances in the liquid such as ethylene glycol, which is also contained in antifreeze, as well as nitrosamine, a substance that can cause cancer in humans, and it is contained in electronic cigarettes in large quantities, and other impurities harmful to humans have been found. Nitrosamines are highly toxic compounds. When ingested, they cause hemorrhages, convulsions, affect the liver, and can lead to coma. Most of the nitrosamines have a strong carcinogenic effect even with a single action, exhibit mutagenic properties.
And one more news: the analysis showed that all cartridges sold as nicotine-free actually contain this harmful substance.
The thermal decomposition of propylene glycol and glycerin contained in the e—cigarette refueling liquid leads to the release of toxic substances — acrolein and formaldehyde. Acrolein irritates the mucous membranes of the eyes and respiratory tract, causes lacrimation, has mutagenic properties. Constant exposure to formaldehyde can lead to mutation of organs. The danger of formaldehyde as a mutagen lies in the fact that it not only induces somatic mutations that are dangerous to the life of the organism, but also in the fact that these mutations accumulate, are transmitted to offspring and appear in the next generations. It has a side effect on the central nervous system, causing headaches, fatigue and depression. It can potentially cause asthma and asthma attacks. Formaldehyde accumulates in the body and is difficult to remove.
E-cigarette vapors cause the same genetic changes as tobacco smoke, in addition, it suppresses the work of other «immune» genes. Scientists have concluded that e-cigarette vapors are stronger than tobacco, affect the immune responses of the mucous membranes, worsen the protective mechanisms of the respiratory system and increase the activity of deadly bacteria.
It is also necessary to mention Periodontists from Ohio State University who found out that electronic cigarettes can provoke various diseases of the oral cavity, ranging from gum inflammation to tooth loss. In addition, the risk of developing cancer is increased among vapers. The study is published in the scientific journal Science Advances.
«Vaping is a serious threat to the oral cavity. Changes occur abruptly and in a short period of time,» says lead author of the study Purnima Kumar.
Scientists took dental plaque samples from 123 young healthy volunteers. This group included non-smokers, vapers, lovers of traditional cigarettes and those who alternate between vaping and cigarettes.
The results of the study showed that electronic vaporizers change the microflora of the oral cavity. The bacteria of fans of such devices are in a state of severe stress and form a thin layer of mucus for survival. As a result, the immune system stops recognizing beneficial bacteria, which leads to the development of diseases of the teeth and gums, explains Purnima Kumar.
In clinically healthy study participants, the microbiome became almost the same as in patients with severe periodontitis, an infection that leads to tooth loss. In addition, in a neglected state, this disease causes problems with the heart and lungs.
Experts also noted that a negative effect is observed when using electronic cigarettes both with and without nicotine. This indicates that the main danger is caused by glycerin and glycol used to create floating clouds.
According to periodontists, the harm from the vaporizer is comparable to smoking ordinary cigarettes. «If you quit smoking and switch to vaping, you will not return to a healthy bacterial profile. In other words, you are not doing yourself any good by trying to give up cigarettes in this way,» explains Purnima Kumar.
According to them, it takes only three to 12 months for the development of radical changes in the oral microflora — less than it happens when smoking cigarettes, changing the diet and even using antibiotics. Changes in the microflora are also felt by the body: Kumar and his co—authors have shown that smokers and vapers have increased amounts of cytokines — signaling molecules indicating the development of inflammatory processes. Moreover, the set of cytokines in smokers and vapers turned out to be different. Scientists believe that for this reason, the diseases caused by electronic cigarettes can be very different from the set characteristic of «traditional» smokers. What these diseases will turn out to be, we still have to find out. 
Discussion.An aggressive marketing policy regarding the safety of electronic cigarettes has been taking place recently. People are told that this is an excellent substitute for regular cigarettes, but research shows that this is far from the case. However, the full range of negative impacts has not been fully studied, since electronic cigarettes are relatively new on the market. We hope that in the near future all the myths about the safe replacement of conventional cigarettes will be dispelled and people, in particular young people, will stop poisoning their bodies.
References1.Gabdulgalieva S.M., Kobzeva Yu.A., Parfenova S.V., Arinina L.V. The effect of electronic cigarettes on the oral mucosa of the Saratov State Medical University named after V.I. Razumovsky of the Ministry of Health of Russia, Department of Therapeutic Dentistry
2. Petrova A.P., Pavlova A.O., Miroshnichenko Yu.D., Sergeev A.A. THE INFLUENCE OF VAPING AND TOBACCO CIGARETTES ON THE ORAL MUCOSA // International Student Scientific Bulletin. – 2018. – No. 1