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Experts interviewed by Good Housekeeping say candles release soot, particles and chemical compounds, but studies of ordinary household use have generally measured emissions below levels of concern. The health effects of candle exposure at particular doses remain unclear; experts recommend ventilation and extra caution for people with asthma or allergies and during pregnancy.
Scented candles release particles and chemical compounds into indoor air, but studies that simulate typical household use have generally found emissions below levels of concern, according to experts interviewed by Good Housekeeping. The report says the health risk is not settled for every situation: room size, ventilation, candle use and individual sensitivity can all affect exposure.
Meghan E. Rebuli, a respiratory toxicologist and assistant professor of pediatrics at the University of North Carolina at Chapel Hill, said candle burning can release soot, particulate matter and volatile or semi-volatile organic compounds. She said studies modeling ordinary indoor use have mostly found those emissions well below thresholds of concern, although some candles may produce more of certain pollutants than others.
Daniel Croft, an associate professor of pulmonary and critical care medicine at the University of Rochester Medical Center, said the exposure depends on how many candles are burning, their size and duration, and the room’s size. The report says researchers have not established a clear threshold for how many candles in a room, or for how long, would create a harmful exposure. Visible smoke or soot can signal particles in the air, but it does not by itself establish that a particular exposure will cause harm.
The report also describes a 2021 study that measured ultrafine particles from five types of pillar candles over six hours. Croft said emissions appeared higher when the candles first began burning and became relatively stable later. The paraffin candle had some of the higher readings in that example, but the reported ranges were similar across the candles. He said earlier research has raised questions about paraffin, so choosing to avoid it is a reasonable precaution while evidence develops.
Ventilation Shapes Candle Exposure
The practical issue is indoor exposure, not simply whether a candle is scented. Croft said ventilation is the most important factor for indoor air quality, because it helps dilute and remove pollutants. Burning multiple candles for a long time in a small or poorly ventilated room could create a different exposure than briefly lighting one candle in a larger, aired space.
Long-term exposure to particulate matter from many sources has been linked in research to asthma attacks, worsening chronic obstructive pulmonary disease, cardiac events, stroke and other neurological conditions, Croft said. Those broader findings do not prove that candle use causes those outcomes: the report says the dose from candles and its health effects have not been firmly established. People with asthma or allergies, and pregnant women, are advised by the experts to pay closer attention to potential air pollution and reduce exposure where practical.
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What Candle Studies Have Measured
The report’s evidence includes studies with different aims, and their findings should not be treated as a single verdict on health effects. A 2021 candle-emissions study examined ultrafine particles from five pillar candles during a six-hour period. The report also cites a 2023 study by the Research Institute for Fragrance Materials on exposure to fragrance materials in air, and a 2025 study that found an increase in certain strains of airborne bacteria after scented candles were burned.
These results address different questions: emissions, fragrance exposure and airborne bacteria are not interchangeable measures of illness or health risk. The supplied report does not give enough detail about the 2025 study’s size, methods or health outcomes to establish what its bacterial finding means for people. It also notes that many studies on particulate matter examine exposure from sources beyond candles, so evidence about those sources cannot by itself quantify candle-related risk.
“The dose makes the poison.”
— Daniel Croft, associate professor at the University of Rochester Medical Center
Exposure Thresholds Remain Unknown
The report says research has not established a precise harmful candle-exposure threshold, such as a number of candles or a burning duration for a particular room size and ventilation level. It is also not clear how findings from individual emissions or bacterial studies translate into illness risk for consumers using candles at home.
Evidence about paraffin is mixed in the report: one study found relatively similar particle ranges across the candle types tested, while earlier research raised concerns about paraffin emissions. The supplied material does not provide the full methods or results of the cited 2023 fragrance study or 2025 bacteria study. Claims about effects from routine use should be read with those limits in mind.
Practical Steps While Evidence Develops
The experts’ immediate advice is to ventilate rooms while burning candles and pay attention to whether smoke, soot or a strong scent accumulates. People with asthma or allergies, and pregnant women, can take added care to limit potential air-pollution exposure, including opening windows when conditions allow. The report does not say consumers must stop using scented candles.
Further research would need to clarify exposure levels across candle types and household conditions, and whether measured emissions lead to meaningful health effects. Until a threshold is established, the effect of candle number, burn time and room ventilation remains central to judging individual exposure.
Key Questions
Are scented candles proven to be harmful?
No specific harm from ordinary use is established in the report. Experts say candles emit particles and compounds, while studies simulating typical household use have generally measured levels below concern thresholds. Researchers have not defined a precise harmful exposure level.
Are unscented candles safer?
The report says scented and unscented candles both release smoke and particulate matter as they burn. Fragrance may add compounds to emissions, but the material does not establish that unscented candles are risk-free or that scented candles cause illness under ordinary use.
Does paraffin wax pose a greater risk?
Evidence described in the report is not conclusive. A 2021 study found some of the higher particle emissions in its paraffin candle example, but readings across the tested candles were in a similar range. Croft said avoiding paraffin is a reasonable precaution for people who prefer to do so while research continues.
How can I reduce exposure when burning candles?
Ventilate the room and avoid letting smoke or soot build up. Exposure also depends on the number of candles, how long they burn and the size of the room. The report does not give a universal safe number of candles.
Source: goodhousekeeping.com
