So-called “third-hand smoke” — nicotine residue that accumulates on clothing, furniture, and other surfaces — can combine with another indoor pollutant to form cancer-causing nitrosamines, according to researchers.

The New York Daily News reported Feb. 9 that researcher Lara Gundel of the Lawrence Berkeley National Laboratory found that smoking residue can combine with ambient nitrous acid, a common indoor pollutant, to form carcinogenic tobacco-specific nitrosamines (TSNAs). Gundel said the chemicals pose the biggest potential hazard to young children, who can absorb TSNAs through their skin, although the cancer risk remains unclear.

Smoking outside doesn’t eliminate the problem, since the residues “follow a smoker back inside and spread everywhere,” said Gundel.

The study was published in the Proceedings of the National Academy of Sciences.