NEW YORK, Dec 5: Burning scented candles to fill the room with the aromas of gingerbread, cinnamon, and pine can certainly create a festive atmosphere, but new research suggests it could pose risks to your health. A study has shown that burning candles significantly impacts indoor air quality, potentially being more harmful to your lungs than exposure to passive smoke.

When candles are lit, they produce a complex mixture of chemicals and particulate matter, including toxic gases like carbon monoxide, sulfur dioxide, and oxides of nitrogen. In addition, scented candles and incense sticks can emit volatile organic compounds (VOCs). Breathing in these substances can cause immediate symptoms such as coughing, sneezing, and eye irritation, and it may exacerbate asthma. Long-term exposure to this indoor pollution has been linked to an increased risk of heart disease, lung cancer, and chronic bronchitis, according to Dr. Asit Kumar Mishra from the University College Cork and Dr. Marie Coggins from the University of Galway, writing in The Conversation.

Burning scented candles has been shown to increase fine particle concentrations—particles that can damage the lungs—up to 15 times the levels deemed safe by the World Health Organization. The study, published in Indoor Environments, analyzed the air quality in 14 homes in Galway, Ireland, both 24 hours before and 24 hours after interventions to improve the homes' energy efficiency.

Researchers measured the concentrations of five pollutants, including CO2 and fine particulate matter smaller than 2.5 micrometers (PM2.5), which can easily enter the lungs. PM2.5 particles, which are invisible to the human eye, can penetrate deep into the lungs and even enter the bloodstream. These particles can be emitted by vehicle engines, wood burning, and smoking.

During the study, pollution-measuring devices were placed a meter away from the floor and sources of pollution, such as candles and ventilation sources. Participants recorded typical household activities like cooking, burning candles, opening windows, and using heating and ventilation systems. The findings revealed that activities like burning candles, smoking, and blocking wall vents had a negative impact on indoor air quality, causing an increase in PM2.5 and CO2 levels. PM2.5 particles can trigger inflammation in the lungs, activating harmful cells that could lead to cancer-causing genetic mutations. The International Agency for Research on Cancer (IARC) classified PM2.5 as a Group 1 carcinogen in 2013 due to its link to lung cancer.

The study also revealed that incense sticks, when burned in equivalent amounts to cigarettes, produce approximately four times as much particulate matter. In non-smoking households, candles may become the main source of indoor pollution, introducing ultra-fine particles into the air. A flickering candle flame produces larger particles and increases the emission of black carbon.

The study further highlighted that burning candles in small, poorly ventilated rooms such as bathrooms or bedrooms exposes occupants to higher pollutant concentrations. In these spaces, higher levels of formaldehyde— a colorless, pungent chemical—were found, which can irritate the upper airways. Surprisingly, scented candles were found to release more fine particles than unscented ones. However, identifying the specific chemicals released by scented candles is challenging, as only 10 percent of the ingredients are disclosed on the product packaging. In both the US and EU, manufacturers are not required to disclose all substances used in scented candles.

Nitrogen oxides, which are also emitted by cars, are a major pollutant produced by scented candles, and they can damage the lungs and airways. Some organic compounds released by home fragrance products, such as benzene, phthalates, and formaldehyde, are known to have carcinogenic properties, according to the American Lung Association. Short-term exposure to these pollutants has been linked to reduced cognitive function, and a 2020 study published in Nature found that chronic exposure to incense smoke may contribute to cognitive decline.

Researchers caution that even opting for candles made from natural ingredients may not shield you from harm, as some natural chemicals can react with ozone in the air, creating potentially toxic byproducts. The experts suggest that burning candles in larger rooms with open windows may mitigate some of the harmful effects, but they stress that more research is needed to fully understand the health risks involved.