Some studies have found that burning incense indoors increase the levels of chemicals called polycyclic aromatic hydrocarbons (PAHs), which have been linked to cancer. This makes sense—burning any sort of organic material, whether tobacco leaves, coal or an incense stick—produces PAHs. But the mere presence of PAHs does not mean that people have a higher risk of cancer. It comes down to the dose. Does burning incense produce enough of these chemicals to actually affect a person’s cancer risk? The largest study so far, looking at incense use and cancer, tracked the health of 61,000 people in Singapore. Although the study claimed to show that people who used incense most heavily were almost twice as likely to develop cancer in their airways than those who did not, the results were weak. The differences between the two groups could have been down to chance, or the fact that people who use incense are far more likely to smoke cigarettes than those who did not. For the most part, the study’s results showed that incense use did not increase the risk of cancer and, even if it did, the rise in risk would be very small. Regardless, anyone wishing to avoid any potential risks could consider burning incense only in situations with good ventilation. Smoking remains the biggest cause of lung cancers and other cancer of the airways. Tobacco smoke contains loads of PAHs, as well as dozens of other cancer-causing chemicals. And smoking can also worsen the effects of other chemicals.