[dev_hugepages]

Nicotine itself is carcinogenic in the mouth:

> Nicotine in tobacco can form carcinogenic tobacco-specific nitrosamines through a nitrosation reaction. This occurs mostly in the curing and processing of tobacco. However, nicotine in the mouth and stomach can react to form N-nitrosonornicotine, a known type 1 carcinogen, suggesting that consumption of non-tobacco forms of nicotine may still play a role in carcinogenesis

[dyauspitr]

The dose in urine is 1-3% of that of cigarette smokers so it is a significant, order of magnitude decrease in risk based on the paper another GP has posted below. In the mouth the levels also seem to be an order of magnitude lower than cigarette smokers (though similar in a majority of cases). Those are relatively acceptable risks for a vice I would think.