Breathe it All In

Theo de Kok of Maastricht University in the Netherlands […] and his collaborators found that PM10 from candles might be especially harmful because, in the body, unidentified constituents of the smoke readily generate free radicals that damage cells. After candles had burned in a Dutch chapel for 9 hours, particles in the air there formed 10 times as many free radicals as airborne particulates collected along busy roadways do, de Kok’s group reported

A study published in 2008 in the medical journal Cancer found that incense use is associated with a statistically significant higher risk of cancers of the upper respiratory tract […] The link between incense use and increased cancer risk held when the researchers weighed other factors, including cigarette smoking, diet and drinking habits. The research team noted that "This association is consistent with a large number of studies identifying carcinogens in incense smoke, and given the widespread and sometimes involuntary exposure to smoke from burning incense, these findings carry significant public health implications."

According to recent research, some laser printers emit sub-micrometer particles which have been associated in other environmental studies with respiratory diseases. An unpublished study at the University of Rostock in Germany is reported to have found that the microscopic particles in toners are carcinogenic, similar to asbestos.