Are Wax Melts Safer Than Candles? What the Research Says

Key Takeaways

• Flame-free doesn't mean emission-free. A 2025 study measured nanoparticle levels from scented wax melts that were similar to those from scented candles, gas stoves and diesel engines (Environmental Science & Technology Letters, 2025).
• The fragrance does it, not the heat and not the wax. When the same researchers warmed an unscented wax melt, they measured no meaningful terpene release and no particle formation at all.
• The mechanism is a chemical reaction in your room. Fragrance compounds called terpenes meet ozone in the air and form brand new particles that weren't emitted by anything.
• This applies to scented candles too, ours included. We sell candles, and the same chemistry runs in a room with one of ours burning in it.
• What you control is fragrance load and airflow, not which device you own. The study ran its tests at two different ventilation rates for exactly that reason.
• The researchers are careful, and so are we. They call for more toxicology work before anyone draws conclusions about harm. This is a measurement, not a verdict.

If you've swapped a candle for a wax warmer to get the scent without the smoke, it's worth knowing what the measurements show. The answer is more interesting than yes or no, and it points at something you can act on.

The short answer

Taking the flame away takes the flame away. It doesn't change what the scent does once it's in the air.

A wax warmer has no open flame, no soot and nothing to knock over and set alight. Those are real gains and worth having. But the scent itself is a chemical release, and in 2025 a team measured what that release does in a real house. The result isn't what the marketing implies.

What the study actually measured

Researchers took measurements in a full-size, ventilated test house at Purdue University. The work was published in the American Chemical Society journal Environmental Science & Technology Letters (full text, 2025).

They tracked two things as they happened: particle sizes down to about one nanometre, and the scent compounds in the air.

Here is what they found. Terpenes given off by scented wax melts react with ozone already in the room, and that reaction builds new particles that nothing gave off directly. The paper calls these new particle formation events.

Counts went above 10⁶ particles per cubic centimetre. The authors describe that as on a par with scented candles, gas stoves, diesel engines and natural gas engines.

They also worked out how much of it lands in the lungs. The dose rates were, in their words, similar to those found for sources that burn something.

The authors put their conclusion bluntly. The results challenge the idea that scented wax melts are a safer choice.

Set the two devices side by side and the split is clear:

What you get	Scented candle	Scented wax warmer
Open flame	Yes	No
Combustion by-products	Yes	No
Knock-over fire risk	Yes	No
Releases terpenes	Yes	Yes
Particles formed with indoor ozone	Yes	Yes, at comparable levels
Usual run time	Until you put it out	Often hours at a stretch

The top half of that table is why people switch, and those reasons are sound. The bottom half is the half that rarely gets mentioned by anyone selling scent, ourselves included.

Why taking the flame away doesn't take the emissions away

This is the bit worth grasping, because it explains why the device isn't what decides the outcome.

Terpenes are the aromatic compounds that give a scent its character, and warming scented wax releases them. Limonene and linalool are two common ones.

Ozone is a reactive form of oxygen that's already in your indoor air. It drifts in from outside and comes off some appliances.

The two react. That reaction makes heavy, slow-moving vapours, and those vapours clump into particles small enough to reach deep into the lungs. Nothing burned. The particles simply assembled in the room.

New particle formation is the name for that process: particles built in the room by a chemical reaction, rather than given off by a source.

There's a twist. Because nothing burns, a warmer gives off none of the nitrogen monoxide that would otherwise break the reaction up. The paper measured it at or below 0.8 parts per billion, low enough for the terpene chemistry to run freely.

That's the mechanism. It needs fragrance and it needs ozone. It does not need a flame.

The unscented test is the finding to act on

The researchers ran a control test, and it makes the practical answer obvious.

They warmed an unscented wax melt in the same warmer, in the same house. No real terpene release. No particles formed. The room's particle profile looked like the background air with nothing going on at all.

So it isn't the warmer, and it isn't the wax. The amount of scent is the variable, and it's the one you can turn down.

For example: two cubes of a strongly scented melt in a closed lounge room gives the reaction plenty to work with. One cube in the same room with a window open gives it much less. Same warmer, same wax, very different afternoon.

What this means for candles, including ours

Full disclosure: Yarra Light makes and sells scented soy candles, so read the next paragraph with that in mind.

The same chemistry runs in a room with one of our candles burning in it. The paper is clear that scented candles give off these compounds as well, and it puts the two side by side rather than singling melts out. So this study hands us no advantage over wax melts, and we won't pretend it does. It describes something that applies to scented products in general, ours included.

If you want the research on candles specifically, we've written up what the studies actually show about candle emissions and indoor air separately.

There's also a labelling angle worth naming. The paper notes that wax melts are marketed as noncombustion, smoke-free and nontoxic. That word does a lot of work and has no defined meaning in Australia, which we've covered in what "non-toxic candle" really means.

What actually reduces what you're breathing

Three things, and none of them is a brand choice.

Airflow. The researchers ran their tests at two different ventilation rates on purpose, because airflow changes the result. Opening a window is the cheapest fix there is.

How much scent. More scent means more terpenes, which means more to react with. A smaller product in a bigger room does less. Unscented does none, as the control run showed.

How long. A warmer left on all afternoon keeps going the whole time. A candle burned for an hour stops when you put it out. This is where the two really differ in daily use, and it's about the habit more than the hardware.

If someone in the house has asthma or another airway problem, those three are the levers to pull, whichever device you prefer.

Does this change anything for pets?

Partly, and in both directions.

A warmer takes away the open flame, and the flame is the risk most pet owners underrate. Cats get onto surfaces other animals can't, and they knock things over. On that one hazard, a flameless device is a real gain.

On the scent side, it's the picture we've set out before. It depends on the animal, and on how the scent reaches it. Cats are less able than other pets to clear certain compounds, which we've covered in candles and cats. The general label question is in what "pet safe" means in Australia.

One limit worth stating. This study measured particles in a test house. It didn't study animals, and nobody should read it as telling you what a wax melt does to a cat.

Frequently asked questions

Are wax melts safer than candles?

They take away the open flame, the soot and the knock-over fire risk, which are real gains. On airborne particles, the 2025 measurements found levels on a par with scented candles, so "safer" doesn't hold as a blanket claim. It depends which risk you mean.

Do wax warmers give off anything if the wax is unscented?

In the study's control run, no. An unscented wax melt gave off no real terpene emissions and formed no particles, and the room matched the background air.

Are wax melts safe for cats?

This research doesn't answer that, because it didn't study animals. The flameless design takes away the knock-over fire hazard, which matters for cats in particular. On scent, the same species questions apply as with any scented product.

Why do particles form if nothing is burning?

Because they're made in the room rather than given off. Scent terpenes react with ozone in the air, and that reaction makes vapours that clump into new particles. It's chemistry after the fact, not smoke.

Does opening a window help?

The study measured at two different ventilation rates for exactly that reason. More fresh air is the simplest lever anyone has.

Should I stop using wax melts?

That's not what the research says, and it isn't our call. The authors say plainly that more toxicology work is needed before anyone draws conclusions about harm. What the study does support is less scent and more airflow, whichever product you use.

Sources

• Jung, Boor et al., "Flame-Free Candles Are Not Pollution-Free: Scented Wax Melts as a Significant Source of Atmospheric Nanoparticles", Environmental Science & Technology Letters, 2025. Open-access full text via PubMed Central.

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