Let's Settle This: Is Burning Candles & Incense At Home Bad For Air Quality?

Last month, Harvard University's School of Public Health released a comprehensive list of 36 research-backed ways anyone can nix toxins at home.

The Healthy Home report contained a lot of advice that you've heard before in mbg headlines: Kick your shoes off at the door, add plants to your space, be mindful of your humidity levels, etc. But its warning on candles gave us pause: "If you use candles or incense, you are creating small combustion sources inside your home," the report reads. "The evidence is clear—in homes with candles or incense burning, there is a sharp increase in airborne particles, sometimes reaching levels that are higher than what is typically measured outside in US cities."

But first, a little background research: One commonly cited chemical of concern in scented candles is limonene, which is naturally found in citrusy notes. While totally safe on its own, when limonene comes in contact with nitrogen oxide—a common pollutant in indoor and outdoor air—it has been shown to lead to byproducts like formaldehyde and acetone. Formaldehyde, in particular, has been identified as a chemical of concern by the Environmental Protection Agency, linked to an increased risk of developing certain cancers.

However, another comprehensive report from the EPA found that in order for candle smoke to surpass the EPA's "excess cancer risk level," you'd have to burn 30 of them in an enclosed room for three hours.

The agency considers a candle's wick to be far more important to its overall safety, writing that wicks made with lead "generate indoor airborne lead concentrations of health concern." Though technically banned from U.S. markets in 2003, you might still find lead wick candles on shelves.

The other important part of candles is the type of wax. Paraffin wax candles (extracted from petroleum) have been found to produce higher levels of alkenes and toluenes than other wax types, though it's unclear whether they emit enough to be a human health concern.

"They probably weren't looking at natural candles and incense," Rhea Mehta, Ph.D., a molecular toxicologist and mbg Collective member said when I told her about the Harvard report. Mehta hesitates to tell anybody to stop burning candles and incense altogether—especially people who use them for religious or spiritual practice.

Instead, choose candles with a "soot-free" wick made of cotton or wood; clean-burning waxes like soy, beeswax, or coconut; and a transparent ingredient list. (Here are a few that pass the test.) As far as incense is concerned, choose ones that have been dipped in natural oils.

Mehta adds that no matter what kind of candle or incense you have, you should be careful when putting it out.

"Usually with candles, the issue is when you blow it out. I tell people to open their windows so smoke doesn't end up in their space—especially if they're about to go to sleep," she says.

Finally, people who are predisposed to respiratory issues or allergies should be extra observant when burning anything at home. "If you notice a headache or drop in energy when you burn a candle, you might not want to keep it close to you," she says.