When a cigarette is lit, the tobacco inside it combusts (burns) to generate smoke, which contains thousands of chemicals. Once it has started, combustion is a self-sustaining process that will continue as long as there is enough tobacco (fuel) and oxygen available.

When burning takes place, the temperature in a cigarette can rise above 800 °C at the tip.
The high temperatures trigger the generation of more than 6000 different chemicals1,2, many of which are harmful or potentially harmful.
Public health authorities have classified several smoke constituents as the likely causes of smoking-related diseases, such as lung cancer, heartdisease and emphysema.
A number of health authorities such as the US FDA, Health Canada and the WHO have developed priority lists detailing the chemicals that are considered to be Harmful and Potentially Harmful Constituents (HPHCs)3,4.
[1] Read the report of the Surgeon General.
[2] The Chemical Components of Tobacco and Tobacco Smoke, Second Edition
[3] About Harmful and Potentially Harmful Constituents (HPHCs)
[4] Read the Tobacco Reporting Regulations (SOR/2000-273)
Read the report of the Surgeon General.
U.S. Department of Health and Human Services, How Tobacco Smoke Causes Disease—The Biology and Behavioral Basis for Smoking-Attributable Disease: A Report of the Surgeon General, Atlanta (GA): U.S. Department of Health and Human Services, Centers for Disease Control and Prevention, National Center for Chronic Disease Prevention and Health Promotion, Office on Smoking and Health (2010).
The Chemical Components of Tobacco and Tobacco Smoke, Second Edition
Alan Rodgman, Thomas A. Perfetti February 25, 2013 by CRC Press
About Harmful and Potentially Harmful Constituents (HPHCs)
HPHCs are chemicals or chemical compounds in tobacco products or tobacco smoke that cause or could cause harm to smokers or nonsmokers. The Food, Drug and Cosmetic Act (FD&C Act) requires tobacco manufacturers and importers to report the levels of harmful and potentially harmful constituents (HPHCs) found in their tobacco products and tobacco smoke.
Read the Tobacco Reporting Regulations (SOR/2000-273)
Minister of Justice Canada Tobacco Reporting Regulations SOR/2000-273 2016
In our tobacco-containing smoke-free products, we are able to precisely control temperatures. This ensures that the tobacco does not reach the temperature necessary for combustion to occur. By avoiding combustion, we reduce or eliminate the formation of HPHCs. It is still necessary to heat the tobacco to release nicotine and flavors from the tobacco.