Cancer can be caused by the incense burnt in Thailand’s Buddhist temples, according to a study that has prompted the health ministry to release a set of guidelines.

Thailand's public health ministry’s set of guidelines suggest that lighting incense in areas that are not properly ventilated should be avoided and that shorter joss sticks that burn quickly should be used. Health officials have sounded the caution to minimize the danger to worshippers and temple workers.
Source-Medindia