Are Soy Candles Safe? What the Research Actually Shows

Key Takeaways

• Every candle puts particles into the air. That's what burning something indoors does. It isn't a fault of any particular wax, and no candle emits nothing.
• How a candle burns is the biggest thing you control. Across five candle types tested under draught-disturbed conditions, particle-phase PAH emissions ranged from 25 to 578 nanograms per hour — a 23-fold spread (Andersen et al., Indoor Air, 2021).
• The first hour of a burn produces more ultrafine particles than the five hours after it (Rasmussen et al., Indoor Air, 2021).
• Fragrance is the bigger variable for sensitive households. In a national survey, 55.6% of asthmatic Australians reported health problems from fragranced products, against 23.9% of non-asthmatics (Steinemann, Wheeler & Larcombe, 2018).
• Four habits do most of the work: trim the wick, keep it out of the draught, ventilate the room, and snuff rather than blow it out.

If you've searched this question before, you've probably found a lot of confident opinion and not much measurement. There is real research on candles and indoor air. It's just less about wax than most articles assume.

Here's what the studies actually measured, and what it means for how you burn a candle at home.

The short answer

Burning anything indoors releases particles. A candle is a small controlled fire, and combustion produces soot, ultrafine particles and trace organic compounds. That's true of every candle on the market.

What the research shows clearly is that the quantity varies enormously — and that most of the variation comes from how the flame behaves, not from what the label says.

A candle with a steady, upright flame emits far less soot than the same candle guttering in a draught. That's the variable in your hands, and it's the one worth your attention.

What "burning badly" does to the air

Stressed burning is the term researchers use for what happens when moving air disturbs a candle flame. The flame flickers, combustion goes incomplete, and soot production climbs.

The most useful study here comes from a team at Lund University and collaborators, published in Indoor Air in 2021. They burned five types of pillar candle in a 21.6 cubic metre chamber, using fluctuating air velocities to simulate a candle sitting in a draught.

Two findings stand out.

First, wax and wick composition did influence emissions of black carbon, PM2.5 and particle-phase PAHs. Composition isn't irrelevant.

Second, and more importantly, all five candle types produced emissions dominated by soot once the flame was disturbed. The authors' conclusion was blunt: preventing stressed burning reduces indoor exposure.

Look at what that range is telling you. The gap between a well-behaved candle and a badly-behaved one is enormous, and it cuts across every type they tested.

That's the practical finding. A draught does more to the air in your room than the wax does.

Every candle emits particles

A companion study in the same journal measured ultrafine particles from five candles under steady burning conditions. Emissions varied between candle types, and the first hour of burning produced higher particle numbers than the following five hours (Rasmussen et al., 2021).

Two things follow from that.

There's no candle that emits nothing, whatever it's made from. And the beginning of a burn is the most active part, which is a good argument for lighting a candle in a room with some air movement rather than a sealed one.

Fragrance matters more than most people expect

Here's where the conversation should be, and rarely is.

Professor Anne Steinemann at the University of Melbourne surveyed a nationally representative sample of 1,098 Australian adults about fragranced consumer products. The results were published in Air Quality, Atmosphere & Health in 2018.

A third of Australians reported some adverse effect. Among asthmatics it was more than half, and 24.0% reported an actual asthma attack following exposure.

One honest caveat, because it matters. That survey covered six categories of fragranced product, including air fresheners, cleaning products and personal care items. Air fresheners were the single largest source of reported effects. Scented candles weren't broken out separately, so you can't read these numbers as candle-specific.

What they do establish is that fragrance sensitivity is common in Australian households, and considerably more common among asthmatics.

If someone in your home has asthma, the fragrance load is the thing to think about first.

What Australian rules actually cover

Australia has no mandatory standard governing candle emissions or indoor air. What does apply is the Australian Consumer Law, under which any product claim has to be substantiable.

There is one candle-specific rule worth knowing. Since 2011, Australia has permanently banned candle holders and decorations that ignite and keep burning for five or more seconds. It covers materials like wood, fabric, feathers, pine cones and paper (ACCC Product Safety).

That one is about fire risk rather than air quality — and fire risk is the more immediate hazard in most homes. It's also the closest thing to a candle-specific regulation on the books here.

We've written separately about what the wording on candle labels actually means and which parts of it you can check for yourself.

Why we use soy wax

There are good reasons to choose a wax, and they're worth stating plainly rather than dressed up.

Factor	Soy wax	Paraffin	Beeswax
Source	Soybean oil, renewable crop	Petroleum refining by-product	Honeybee hives, renewable
Biodegradable	Yes	No	Yes
Vegan	Yes	Yes	No
Typical melt point	Lower, around 45 to 52°C	Higher, around 46 to 68°C	Highest, around 62 to 65°C
Washes out of fabric	Yes, with warm soapy water	Harder, needs heat or solvent	Harder

Renewable feedstock, biodegradability and a cooler pour are real, checkable properties. The lower melt point is also why soy candles frost and develop surface marks, which we've covered in our piece on frosting and other soy wax imperfections.

Those are the reasons we pour soy. They're about the material and the making, and they hold up on their own.

How to burn any candle cleanly

This is the part that actually changes what ends up in your air, and it works whatever your candle is made from.

• Trim the wick to about 5mm before every burn. A long wick produces a tall, unstable flame, and instability is what generates soot.
• Keep it out of draughts. Away from open windows, doorways, fans and air conditioning vents. This is the single highest-impact habit, and it's what the Indoor Air stressed-burning research points to directly.
• Ventilate the room. Not a gale — just some air exchange that isn't blowing across the flame.
• Watch for a flickering or smoking flame. That's the candle telling you it's burning badly. Extinguish it, trim the wick, relight.
• Don't burn for more than about four hours at a stretch. Longer burns let the wick mushroom and destabilise.
• Snuff rather than blow it out. Blowing sends a plume of unburnt particles straight into the room.
• Be more careful in small or closed rooms, and around anyone with asthma. Concentration depends on room volume, so the same candle behaves differently in a bedroom than in an open-plan living area.

If you have pets there's a separate set of considerations, particularly around essential oils. We've written about candles in homes with cats and candles around dogs.

What to look for when you buy

The useful information is rarely on the front of the label. These are the things worth checking:

• A stated wax type and percentage. "Soy blend" can mean almost anything.
• Wick material. Cotton or wood, and free of any metal core.
• What's in the fragrance. Whether it's essential oil, fragrance oil, or a mix, and whether it's phthalate-free.
• A maker who'll answer questions about any of the above without deflecting.

That last one is the real test, because it's the one you can actually apply. A maker who knows their materials will tell you about them.

Frequently asked questions

Does the type of wax change how much soot a candle makes?

Composition does influence emissions — the 2021 Indoor Air research found it affected black carbon and PM2.5. But burn conditions matter more. The same study found all five candle types produced soot-dominated emissions once air movement disturbed the flame. A candle in a draught will out-soot the same candle burning steadily, by a wide margin.

Are scented candles safe if someone in the house has asthma?

Use caution. In the 2018 Australian survey, 55.6% of asthmatics reported health problems from fragranced products and 24.0% reported an asthma attack. That data covers fragranced products broadly rather than candles specifically, so treat it as a reason for care rather than a candle-specific finding. Unscented candles, good ventilation and shorter burns all reduce the exposure.

Is it safe to burn candles every day?

For most people in a ventilated room, occasional daily use is unlikely to be a concern. The things that raise exposure are small closed rooms, long unbroken burns, draught-disturbed flames and several candles at once. If you're burning multiple candles daily in a closed bedroom, that's worth reconsidering.

Does a wooden wick burn cleaner than cotton?

There's no good evidence that it does. Wooden wicks are chosen mostly for the crackle and the look. What matters is that the wick is correctly sized for the vessel and the wax, and that it has no metal core. An oversized wick of any material burns hot and unstable.

Why does my candle smoke when I blow it out?

Because blowing disperses the unburnt fuel in the wick as a visible plume. A snuffer cuts the oxygen instead, so the flame stops without the smoke. It's a small change that makes a noticeable difference in a small room.

The bottom line

The research points somewhere less exciting than most candle articles suggest, and more useful.

Every candle emits particles. How much depends far more on the state of the flame than on the label, and the flame is the part you control. Trim the wick, move it away from the draught, open a window, and snuff it rather than blowing it out.

That combination does more for the air in your house than anything printed on the front of the jar.

---

Julia hand-pours every Yarra Light candle in Melbourne. Ours are 100% soy wax with FSC-certified wood wicks and phthalate-free fragrance oils made in Australia. This article is general information about candles and indoor air, not medical advice.