I know this is an old thread but want to make a clarification for posterity.
Burning any organic material generates carcinogenic chemicals, among other toxic chemicals. Carcinogenic chemicals (known or suspected) include petrogenic hydrocarbons with one or more benzene rings. These can form in various isomers as a result of burning plant matter or other material.
Nicotine itself, if I'm remembering correctly, may also be a carcinogen.
BUT - here's the most important thing - carcinogenic chemicals won't give you cancer from single or even infrequent exposure. Carcinogens cause cancer when they are repeatedly ingested on a regular basis.
So you can smoke tobacco without getting cancer, so long as you avoid becoming addicted and smoke infrequently. The true risk of developing cancer comes with developing an addiction, resulting in exposure many times per day over decades.
Also, there maybe pesticides in mainstream tobacco that are carcinogens. However, the additive people speak of is typically ammonia NH3) which reacts with nicotine in the same way the OH in NaOH (lye) reacts with the H in DMT, causing said molecule to lose its H, converting it from a salt to a free base. Freebase substances have a much lower and greater window at which they will vaporize, compared to the salt form. Thus, you get a bigger dose per drag/hit.
