<unk>  (abbreviated<unk>  is a nitrosamine found in tobacco that has been classified by the IARC as a Group 2B carcinogen.
Although no adequate studies of the relationship between exposure to<unk>  and human cancer have been reported, there is sufficient evidence that<unk>  causes cancer in experimental animals.<unk>  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.<unk>  is produced by the nitrosation of nicotine during the curing, ageing, processing, and smoking of tobacco. Roughly half of the<unk>  originates in the unburnt tobacco, with the remainder being formed during burning.
Some of the<unk>  present in the saliva of tobacco users is produced endogenously from nitrite in saliva and tobacco alkaloids including nicotine.
N-Nitrosonornicotine
Cyclochlorotine
Nicotinyl alcohol
Methyl isocyanate
Acrolein
Methanol
Nicotine
Nicotine 