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 and e-cigarette 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.