Most people don't think of going to a place of religious worship as a time when they're exposing themselves to the danger. However, it really depends where you worship.
A recent study by a Thai doctor found that burning insence in shrines and temples fills the air with cancer-causing toxic chemicals. Dr Manoon Leechawengwong, who completed the study, found that those chemicals are as bad as traffic fumes and cigarette smoke.
Joss sticks are a type of incense used in many East Asian countries, often burned as an offering. It is believed that their smoke carries prayers to the deceased through its journey upward into the sky.
The two year study of temple workers found that the workers are exposed to a mix of chemicals from the smoke that put them on risk for numerous diseases, including several different cancers. The study also found some DNA changes.
One way to reduce the chemical exposure would be to put the sticks out right after use, instead of letting them burn down completely. This way, the ritual can be preserved, and the pollution is reduced.