Inhaling any burned plant material causes a slight increase in (primarily lung) cancer risk.
Inhaling burned tobacco has an above average ability to cause cancer.
Common commercial cigarettes, in general, have other ingredients that become carcinogenic when burned.
Nicotine, while not directly cancer causing, depresses the immune response in the affected areas, increasing cancer risk in those areas. This also affects chew, gum, inhalers, etc. Due to the nature of the rapid regeneration of the mouth and throat, this is likely a significant factor in the increased caused risk for chewed tobacco.
Additionally, chewed tobacco can cause Leukoplakia, which increases the risk of Oral cancer.
Cancer risk (most to least): Smoking, chew/dip, inhalers, gum, snuff.
