 Frankincense and myrrh date back to thousands of years before the three wise men, the burning of which is incense may have actually had a hygienic function, like maybe repelling mosquitoes, and when put to the test incense fumes were able to kill off some bacteria and mold in the air, but may also carry health risks. Although the adverse health effects of second-hand tobacco smoke are well-recognized, the impact of burning incense in the home has received less attention, but burning incense has been found to generate like four times the particulate matter as cigarette, so incense maybe even works. No wonder home incense used may have significant adverse health effects, particularly in the heart and lungs, including childhood asthma. No wonder since the incense smoke particle size peeks down in the danger range, so ultrafine they can float down to the deepest parts of the lungs. It's not just the little ash particles in the smoke, though. There's carbon monoxide, nitric oxides, sulfur dioxide, carcinogenic polycyclic aromatic hydrocarbons, and volatile organic compounds like benzene and formaldehyde. The World Health Organization suggests limiting indoor formaldehyde to about 80 parts per billion, but even when the window opened during the hour or so incense is burning, formaldehyde levels exceed the safety limit. What does this all mean in terms of disease outcomes? Studies on rats show incense can do all sorts of terrible things, but what about people? A study of thousands of children followed over time, found that exposure to household incense burning was associated with impaired lung function, reduced lung function growth, and increased risks of respiratory diseases and symptoms. Daily exposures associated with impaired lung function in adolescents, too, though interestingly those who had pets at home appeared to have better lung function, something I noted previously, how having a dog or cat in the house during early life may protect against childhood asthma analogy. What about the heart? Long-term exposure to incense burning in the home environment was associated with an increased risk of cardiovascular mortality. Approximately 8% of heart disease deaths and 12% of stroke deaths could potentially be attributed to incense use, though they were looking at long-term exposure, so like incense burning at home on a daily basis for more than 20 years. What about cancer? Temple workers exposed to incense day in and day out were found to have evidence of significantly more DNA damage, including DNA strand breaks. Does this translate into greater cancer risk? One unsolved mystery has been why non-smoking Asian women have such high lung cancer rates. Might it be incense? Probably not, since the association between incense use and lung cancer remains inconclusive. Though incense use does appear to be linked to cancers of the upper respiratory tract, as well as brain tumors among children whose mothers were exposed to incense. Three times the odds even more than that of secondhand smoke. In fact, even more than the consumption of baloney sandwiches. Process meat consumption only appears to at most double brain tumor risk among children. Even without tumors, a study of 15,000 infants found that household incense burning was associated with a delay in brain development milestones, such as when they start to walk. And then on the other side of the life cycle, incense exposure among older adults was associated with reduced cognitive performance and adverse structural changes in the brain. The researchers conclude that this calls for safer practices, such as avoiding burning incense indoors or using safer incense alternatives. So-called environmentally friendly types of incense have been put to the test, and they were found to contain even higher concentrations of several potentially carcinogenic polycyclic aromatic hydrocarbons. Despite being a recognized health hazard, burning incense remains in widespread use. And at the very least, we may want to avoid burning incense in the home when susceptible individuals are present, such as the very young, the very old, or people with a family history of allergies or pre-existing cardiovascular or respiratory disease. One innovative suggestion is electronic incense, like the e-cigarette of the incense world, so you get the fragrance without the combustion byproducts of smoke. Most of the concern about e-cigarette-related adverse events traditionally have evolved around the nicotine, which wouldn't be a problem with e-incense, the concern that e-cigarette use would lead to real cigarette use. But now that there have been thousands of cases of lung injury associated with vaping, and we're still actually not sure what's causing the issue, it seems to me we should figure that out before we push for the electronic incense equivalent. One option in the meantime is scented candles, which, under normal conditions of use, do not appear to pose known health risks to the consumer.