N-Nitrosonornicotine (NNN) is a nitrosamine produced during the curing and processing of tobacco and has been classified by the IARC as a Group 1 carcinogen. Although no adequate studies of the relationship between exposure to NNN and human cancer have been reported, there is sufficient evidence that NNN causes cancer in experimental animals. NNN is found in a variety of tobacco products including smokeless tobacco like chewing tobacco and snuff, cigarettes, and cigars. It is present in smoke from cigars and cigarettes, in the saliva of people who chew betel quid with tobacco, and in the saliva of oral-snuff users. NNN is produced by the nitrosation of nornicotine during the curing, aging, processing, and smoking of tobacco. Roughly half of the NNN originates in the unburnt tobacco, with the remainder being formed during burning.
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