Nicotine-derived nitrosamine ketone (NNK) is one of the key tobacco-specific nitrosamines derived from nicotine. Endogenous nitrosamine formation can be inhibited by ascorbic acid. Nitrite and nitrosamine intake are associated with risk of gastric cancer and oesophageal cancer. Non toxic 4-IPO analogues are also capable of inhibiting nicotine-derived nitrosamine ketone (NNK) metabolism. Vitamin C may prevent some cancers by inhibiting the formation of mutagenic N-nitroso compounds (nitrosamine). Around 1970, it was found that ascorbic acid (vitamin C), an antioxidant, inhibits nitrosamine formation. Ascorbate, which is added to cured meat, however, reduces nitrosamine formation. "N"-Nitrosonornicotine (NNN) is a tobacco-specific nitrosamine produced during the curing and processing of tobacco. However, this toxic nitrosamine has only rarely been identified in cosmetic products. However, smoked salmon is not a major source of nitrosamine exposure to humans. Nitrosamine formation in beet juice can reliably be prevented by adding ascorbic acid. Among the tobacco-specific nitrosamines, nicotine-derived nitrosamine ketone (NNK) and "N"-nitrosonornicotine (NNN) are the most carcinogenic.