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Candles release smoke particles and other compounds, but studies of typical household use have generally found emissions below levels of concern. Experts say exposure depends on factors such as how many candles are burning, how long they burn, room size and ventilation; a precise threshold for harm has not been established.
Scented candles release smoke particles and airborne compounds, but studies of candle burning that approximate normal household use have generally found emissions below levels of concern, according to experts interviewed by Good Housekeeping. The experts say exposure varies with the number of candles, burn time, room size and ventilation, while evidence has not established exactly what level of exposure causes harm.
Meghan E. Rebuli, a respiratory toxicologist and assistant professor of pediatrics at the University of North Carolina at Chapel Hill, told Good Housekeeping that candle burning can release soot, particulate matter and volatile or semi-volatile organic compounds. She said studies simulating typical household use have mostly measured levels well below thresholds of concern, regardless of candle type. Some studies have found higher emissions from certain candles, including fragranced or paraffin-based products, but Rebuli said those levels are not likely to be a major concern.
Daniel Croft, an associate professor of pulmonary and critical care medicine at the University of Rochester Medical Center, said the health implications depend on exposure. How many candles are burning, their size, how long they burn and the size of the room all affect what people breathe. Research on particulate matter links long-term inhalation to health problems including asthma attacks, worsening chronic obstructive pulmonary disease, and increased risks of cardiac events and stroke. That evidence concerns particulate matter broadly; it does not establish that ordinary candle use causes those outcomes.
The report also cites a 2025 study that found an increase in certain strains of airborne bacteria after scented candles were burned. It does not establish from the information provided whether that finding leads to illness. A 2021 study measured emissions from five types of pillar candles over six hours. Croft said emissions appeared higher when candles first began burning and later became relatively stable; the paraffin candle had some higher particle emissions, but results for the candles were in a relatively similar range.
Ventilation Shapes Candle Exposure
The practical concern is indoor exposure, not simply whether a candle is scented. A candle used briefly in a ventilated room does not create the same conditions as several candles burning for hours in a small, stuffy space. Croft told Good Housekeeping that ventilation is the most important factor in indoor air quality. Opening windows or otherwise improving airflow can reduce the buildup of emissions.
People with asthma or allergies, and pregnant women, may wish to pay closer attention to potential air pollution exposures, the experts said. This is a precautionary recommendation, not evidence that candle use has been shown to cause a specific pregnancy or allergy outcome. The available information does not identify a universal safe number of candles or a burn-time limit that applies to every room.
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What Candle Studies Have Measured
Candle flames can produce visible smoke or soot, but exposure is not determined by visibility alone. Croft said the amount of particulate matter people inhale depends on the candle and the conditions in which it burns. He described the toxicology principle that “the dose makes the poison”: the quantity and duration of exposure matter when evaluating potential effects.
Research cited in the report has examined different parts of the issue. The 2021 candle-emissions study compared particle emissions from five pillar candles over six hours. The report also references a 2023 Research Institute for Fragrance Materials study on consumer exposure to fragrance materials in air, as well as the 2025 study on airborne bacteria. These studies address different measures; none, as summarized in the report, establishes a specific candle-use threshold for health harm.
Good Housekeeping also cites a 2021 study comparing carbon dioxide from two candles with carbon dioxide exhaled by a person. Croft used it to illustrate that candles contribute to what accumulates indoors and that ventilation helps clear indoor air. The comparison does not define a health-risk threshold for candle emissions.
“The number of candles you’re lighting, the size of the candle, the duration that it’s burning, the size of the room—that would all matter in terms of what the exposure would look like.”
— Daniel Croft, associate professor at the University of Rochester Medical Center
No Candle-Specific Harm Threshold
Researchers have not established how many candles, in what size room, or for how long would cause harm, according to the report. Findings also vary by the emissions measured and the conditions tested. The cited evidence does not settle whether scented candles present a greater health risk than unscented candles in ordinary use, or what the 2025 finding about airborne bacteria means for illness risk.
Experts’ broader warnings about long-term particulate exposure should not be read as proof that typical candle use causes asthma, heart disease or stroke. The available material does not give a definitive risk estimate for particular groups or a clear safety cutoff. Individual sensitivity and room ventilation remain relevant, but their effects have not been quantified here.
Further Research and Safer Use
The evidence summarized by Good Housekeeping does not point to a single, confirmed threshold or a change in official guidance. More research would be needed to connect candle-specific emissions and exposure levels with health outcomes, including to clarify the significance of findings on fragrance compounds and airborne bacteria.
For now, the experts’ practical advice is to use candles in well-ventilated spaces and pay attention to smoke, soot or an overpowering scent. People with asthma or allergies, and pregnant women, can reduce possible exposure by limiting candle use or improving airflow. The report does not offer a precise burn-time rule or a specific number of candles that can be considered safe in every setting.
Key Questions
Are scented candles proven to be harmful?
No. The studies of candle burning that approximate normal household use have generally found emissions below levels of concern, according to the experts cited. The evidence does not establish a candle-specific level at which harm occurs.
Are paraffin candles more dangerous than other candles?
The report describes some research in which paraffin candles had higher particle emissions, but results across the tested candles were relatively similar. A clear verdict on comparative health risk has not been established in the material provided.
What matters most when burning candles indoors?
Ventilation, the number of candles, burn duration and room size affect exposure. Croft identifies ventilation as the most important factor for indoor air quality.
Should people with asthma avoid candles?
The experts advise people with asthma or allergies to pay closer attention to possible air pollution exposures and to reduce them where practical, such as by opening windows. The report does not say that candle use has been proven to trigger illness in every person with asthma.
Source: goodhousekeeping.com
