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.  Incense is usually derived from fragrant plant materials, like tree bark, resins, roots, flowers and essential oils. A recent study conducted and presented by the researchers of the department of epidemiology from Copenhagen’s Statens Serum Institut, shows that there is a connection between the exposure to burning incense and airway cancers. Long-term Exposure to Incense Raises Cancer Risk Incense burning produces particulate matter and is known to contain possible carcinogens such as polyaromatic hyodrcarbons (PAHs), carbonyls and benzene.  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.”Given that our results are backed by numerous experimental studies showing that incense is a powerful producer of particulate matter and that incense smoke contains carcinogenic substances, I believe incense should be used with caution,” said study author Dr. Jeppe Friborg, of the department of epidemiology research at Statens Serum Institute in Copenhagen, Denmark. “That is, frequent use in rooms where people live should be minimized, or at least sufficient ventilation should be secured. In our study, we find the increased risk of cancer to be present in individuals reporting frequent use of incense for many years, thus, repeated exposure for years should probably be avoided.” Incense burning almost doubled the risk of developing squamous cell upper respiratory tract carcinomas including nasal/sinus, tongue, mouth and laryngeal. There was an increased risk both in smokers and in nonsmokers, pointing to an independent effect of incense smoke.

 http://health.usnews.com/articles/health/healthday/2008/08/25/long-term-exposure-to-incense-raises-cancer-risk.html