Aug. 25, 2008 -- People who breathe burning incense over long periods have an increased risk of developing certain cancers, even if they don't smoke cigarettes, a new study shows.
Long-term exposure to incense fumes was associated with an increased risk for most upper respiratory cancers, as well as squamous cell lung cancer, the study shows. Squamous cell lung cancer is most common type of lung cancer in smokers.
The risk was seen in smokers and nonsmokers, suggesting that exposure to burning incense is an independent risk factor for certain cancers of the respiratory tract, says lead researcher Jeppe T. Friborg, MD, PhD, of Copenhagen's Statens Serum Institut.
"The findings from this study and the experimental research are sufficient to recommend that people avoid prolonged use of incense in areas where they spend a lot of time, like living rooms," Friborg says.
Daily Incense Use Common
Used since biblical times, incense is still an integral part of daily life in large parts of Asia and India. And many people in the U.S. and other Western countries also burn incense on a daily basis.
A wide variety of plants and oils are used to make incense. When burned, many of these mixtures have been shown to produce some of the same carcinogens that are found in cigarette smoke.
Because of this, a number of studies have examined a possible link between incense inhaled into the lungs and lung cancer, but the findings have not been conclusive.
The newly published study is the first to follow healthy people over time in an effort to understand the impact of long-term exposure to burning incense on cancer risk.
More than 60,000 Chinese residents of Singapore who were participants in a larger health study were followed from enrollment (which occurred between 1993 and 1998) and 2005.
None of the study participants had cancer at enrollment, and all were interviewed in detail about their dietary and lifestyle habits, including their exposure to incense.
Roughly three-quarters of the men and women reported being current incense users.
Over the course of the study, 325 upper respiratory tract cancers and 821 lung cancers were reported.
Long-term and frequent exposure to incense fumes was associated with a significant increase in the risk of squamous cell cancers of the upper respiratory tract.
Risk Small for Casual Users
Daily exposure to burning incense is common in Asia, but it is not limited to the East.
To illustrate the point, Friborg and colleagues cite a 2004 study involving non-Asian minority women living in New York City. More than a quarter of the women (28%) reported burning incense during pregnancy, and incense exposure was identified as a significant source of exposure to a commonly inhaled carcinogen.
American Cancer Society Deputy Chief Medical Officer Len Lichtenfeld, MD, tells WebMD that the study should not alarm casual incense users who do not appear to be at significant risk.
But he adds that people who breathe burning incense on a daily basis need to understand the risk.
"Daily exposure is associated with an increase in upper airway cancer," he says. "This a real risk that should not be ignored."