Sweetened vanilla, calming lavender, or fragrant jasmine and lotus may fill your home with enticing aromas. But new research shows that the supposed stress-reducing and mood-enhancing effects of scented products may come with unwanted indoor pollution.

“While these products are widely used to create a cozy atmosphere, their emissions can impact indoor air quality, especially in spaces with limited ventilation,” says Nusrat Jung, a civil engineer at Purdue University.

Jung became interested in the quality of our indoor atmosphere after walking through grocery store aisles that had scented candles, wax melts, and other fragrance-releasing items.

“These products are marketed as safe and clean, but we wanted to investigate what else they might be releasing into the air besides pleasant scents,” she says.

Scented Wax Melts and Pollution

In research published recently in Environmental Science & Technology Letters, Jung and her colleagues examined the effects of scented wax melts that are often advertised as pollution-free. They used a laboratory recreation of a typical home at Purdue filled with sensors that could monitor the kinds of chemicals inside.

Scented products have released volatile organic compounds and terpenes — chemicals responsible for everything from aromatic essential oils to the skunk-like smell of marijuana. But previous research by Jung and her colleagues revealed that flame-free candles, or wax melts, release more terpenes than candles with flames.

Once released, terpenes react with ozone in the air and form nanoparticles.

“These particles, despite being formed in a non-combustion process, reached levels that pose potential respiratory risks, challenging the perception of scented wax melts as a benign household product,” Jung says.

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Do All Scented Products Cause Indoor Pollution?

While the team’s recent study looked at flame-free scented candles, previous work from Jung examined the impact that other fragrant products have on indoor air quality.

Her team found in an earlier study that hair products like sprays persisted for a while indoors, especially after being exposed to devices like hair curlers or straighteners.

In fact, Jung’s work shows that scented products in general are significant contributors to indoor pollution. In one study they found that scented products can create more breathable nanoparticles than gas stoves or diesel engines.

It may not be limited to homes. Scented products like air fresheners often used in cars release many of the same volatile organic compounds to mask lingering stench — all in a relatively smaller area than your average home. But Jung hasn’t specifically studied these potential impacts, and said further research would be needed to get a clearer idea of any problems they might be causing.

Health Problems from Scented Products

The types of health problems these chemicals can cause isn’t entirely clear, but they may pose issues for our breathing systems — some of them long-term.

“Some [volatile organic compounds] are classified as hazardous air pollutants, while airborne nanoparticles have been linked to lung inflammation, cardiovascular effects, and other adverse health outcomes,” Jung says.

She noted that actual exposure from these potentially harmful chemicals might vary based on a number of factors, though.

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What to Avoid

Other recent research has found homes vary greatly in their amount of indoor air pollution. Ventilation, occupancy patterns, and household location can all effect how polluted homes are. The authors of that paper say that monitoring indoor pollution in your home is becoming increasingly important, as a result.

“With more time spent working from home, understanding the factors that affect air quality within households is increasingly important,” said Owain Rose, a coauthor of the paper, in a press release.

Jung has recommended always keeping on exhaust fans such as those above stoves or in bathrooms when using these products. But the best thing would be to avoid hair care products, or scented candles, and waxes altogether.

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Joshua Rapp Learn is an award-winning D.C.-based science writer. An expat Albertan, he contributes to a number of science publications like National Geographic, The New York Times, The Guardian, New Scientist, Hakai, and others.