N-Nitrosonornicotine

N-Nitrosonornicotine (abbreviated NNN) is a nitrosamine found in tobacco that has been classified by the IARC as a Group 2B carcinogen.

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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 chewing tobacco, 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 nicotine during the curing, ageing, processing, and smoking of tobacco. Roughly half of the NNN originates in the unburnt tobacco, with the remainder being formed during burning.

Some of the NNN present in the saliva of tobacco users is produced endogenously from nitrite in saliva and tobacco alkaloids including nicotine.