THS is a newly described health risk.Evidence supports its widespread presence in indoor environments.However, its genotoxic potential, a critical aspect in risk assessment, is virtually untested.An important characteristic of THS is its ability to undergo chemical transformations, as demonstrated in a recent study showing that sorbed nicotine reacts with the indoor pollutant nitrous acid (HONO) to form tobacco-specific nitrosamines (TSNAs), 4-(methylnitrosamino)-4-(3-pyridyl)butanal (NNA) and 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanone (NNK).