Watch out, stoners!  You cover up may be causing cancer.

Burning incense may create a sweet scent, but regularly inhaling the smoke could put people at risk of cancers of the respiratory tract, researchers reported Monday.

In a study of more than 61,000 ethnic Chinese living in Singapore who were followed for up to 12 years, the investigators found a link between heavy incense use and various respiratory cancers.

Incense is usually derived from fragrant plant materials, like tree bark, resins, roots, flowers and essential oils. Past research has found that burning these materials can produce potentially cancer-causing substances, including benzene and polyaromatic hydrocarbons.

However, no studies until now had linked the practice of burning incense to an increased cancer risk over time, according to the researchers, led by Dr. Jeppe T. Friborg of the Statens Serum Institute in Copenhagen.