"Nitrosamine occurs in latex products such as balloons,[1] and in many foods and other consumables. 
Nitrosamines from condoms are not expected to be of toxicological significance."
"In foods, nitrosamines are produced from nitrites and secondary amines, which often occur in the form of proteins. Their formation can occur only under certain conditions, including strongly acidic conditions such as that of the human stomach. High temperatures, as in frying, can also enhance the formation of nitrosamines. The presence of nitrosamines may be identified by the Liebermann's reaction."
"Under acidic conditions the nitrite forms nitrous acid (HNO2), which is protonated and splits into the nitrosonium cation N≡O+ and water: H2NO2+ = H2O + NO+. The nitrosonium cation then reacts with an amine to produce nitrosamine."
"These processes lead to significant levels of nitrosamines in many foodstuffs, especially beer, fish, and fish byproducts, and also in meat and cheese products preserved with nitrite pickling salt. The U.S. government established limits on the amount of nitrites used in meat products in order to decrease cancer risk in the population.[citation needed] There are also rules about adding ascorbic acid or related compounds to meat, in order to inhibit nitrosamine formation."
"Nitrosamines can also be found in tobacco smoke, American dip snuff and to a much lesser degree, snus. (127.9 PPM for American dip snuff compared to 2.8 PPM in Swedish snuff or snus)."