How Long Is Too Long To Keep A Candle Burning? Toxicology Experts Weigh In

The first thing to consider when deciding how long to keep candles lit is air quality. Lara Adler, an environmental toxins expert and certified holistic health coach, tells mbg that scented candles can release small particles like benzene, toluene, and formaldehyde into the air—all of which are harmful to health in high doses.

According to a recent New York Times investigation, research shows that burning a candle at home is unlikely to emit enough particulate matter to harm health. However, Adler points out that indoor air pollution is always more of a concern during the winter months, “when we tend to keep our windows closed throughout the day.”

So if you notice that you have an irritated, itchy throat, watery eyes, or headache after lighting up a scented candle, it’s a sign to blow it out and switch to an unscented option. (Adler vouches for small, unscented beeswax tea lights.)

Beyond that, it should be safe to burn for up to four hours with a window cracked open as an extra precaution. (Toxicology experts recommend opening windows from time to time in winter anyways, to keep indoor air from getting too stuffy.)

After four hours, manufacturers note that most candles will begin to lose their scent. Candle wicks will also begin to mushroom, which can lead to an uneven burn.

Candles made from petroleum-derived paraffin wax tend to be worse for air quality (and the planet) than ones made from cleaner-burning waxes. We recommend opting for candles made from soy or beeswax, scented using naturally derived essential oils, and labeled phthalate-free. (Here are some of our top picks for winter.)

Adler notes that even the cleanest-burning candles can aggravate those with sensitivities. “All candles, regardless of whether they have additive colors or scents, and whether those scents are synthetic or natural, produce particulate matter when burned,” she says. “Even in the absence of phthalates, many compounds used in fragrance formulations are allergens and can act as asthma triggers.” For this reason, it’s important to pay attention to how your body feels when a candle is burning.

To minimize the risk of a reaction, you can open more windows, place the candle further away from you, or move to a larger room with better ventilation.

Molecular toxicologist Rhea Mehta, Ph.D., previously told mbg that the smoke that comes from a candle after you blow it out can be especially high in particulate matter. She recommends putting the candle next to an open window after you blow it out to let the smoke escape—especially if you’re about to go to sleep.