Scented candles can make a room feel inviting, but burning them may also add fine particles and volatile organic compounds to indoor air. The level of exposure depends on the fragrance, wick, burning conditions, room size and ventilation.
A 2026 study of 112 homes in London, published in Environment International, found that candles, incense and oil diffusers could cause indoor fine-particle levels to rise. Candle use was estimated to account for 14% of bedroom PM2.5 exposure in homes where candles were used; some hourly readings reached 622 micrograms per cubic meter.
Flame-free does not mean emission-free
Research by Purdue University, published in Environmental Science & Technology Letters, found that scented wax melts can also generate large numbers of airborne nanoparticles. The researchers linked their formation to fragrance compounds called terpenes, which can react with ozone indoors. An unscented wax melt did not produce the same pattern in the experiments.
These findings do not establish that occasional candle use causes illness. A 2014 risk assessment found no known health risk under typical conditions, while researchers say more evidence is needed to understand long-term exposure. People with asthma or fragrance sensitivities may be more affected by scented products.
How to use candles thoughtfully
Opening windows or otherwise improving air circulation can help disperse indoor emissions. Avoid burning several candles at once in small rooms, keep wicks trimmed to limit smoke and consider unscented options if fragrance causes discomfort. Wax type alone does not determine emissions, and wax melts can also affect air quality.
As homes become more energy-efficient, ventilation and indoor-air monitoring may play a growing role in making comfortable living spaces healthier.
