What’s Really in the Air When You Light That Scented Candles

Take a closer look at the hidden chemistry behind your favorite evening ritual and learn what you can do about it, all backed by science

It’s 9 p.m. After a long day of emails, deadlines, and the usual chaos, you dim the lights, strike a match, and light your favorite scented candle. The soft glow flickers. Lavender and vanilla fill the room. You let out a deep breath.

This small ritual, repeated in millions of homes every evening, feels like the definition of self-care. But what if the very thing you use to relax is quietly filling your living room with pollutants you can’t see, smell, or taste?

The truth is more complicated and more interesting than a simple “candles are toxic” headline.

The Invisible Chemistry of a Burning Candle

When you light a candle, you’re not just creating ambiance. You are starting a small chemical reaction called incomplete combustion. This is the same basic process that powers car engines and coal plants, just on a much smaller scale. Like those bigger sources, candles produce by-products that go into the air.

A landmark 2025 study published in Nature Scientific Reports measured what happens when a scented candle is lit in a real residential room. The results were striking: particulate matter concentrations spiked, with PM₁₀ reaching 42.8 micrograms per cubic metre at three metres from the candle. The finer particles PM₂.₅ and PM₁ didn’t just hover near the flame. They travelled throughout the room, staying airborne long after the larger particles settled [1].

To put that in perspective, the World Health Organization’s annual air quality guideline for PM₂.₅ is just 5 µg/m³. A single candle session can push your indoor air well above that threshold.

The U.S. EPA has been flagging this since 2001, documenting candles as a recognised source of indoor air pollution that produces soot and volatile organic compounds (VOCs),  including benzene and formaldehyde [2].

Hong Kong’s own Environmental Protection Department explicitly lists “burning candles” as a source of indoor particulate matter in its official guidance on indoor air pollutants [3].

Paraffin: The Petroleum in Your Living Room

About 95% of candles on the market are made from paraffin wax, which is a byproduct of petroleum refining. The same crude oil that becomes gasoline also becomes the wax in your lavender-vanilla jar candle. Paraffin is cheap, burns evenly, and holds fragrance well, which is why the industry prefers it [4].

But when paraffin burns, it doesn’t just produce wax vapour. A 2009 study from South Carolina State University, presented at an American Chemical Society symposium, found that paraffin candles emitted a cocktail of chemicals including benzene, toluene, and formaldehyde, all classified as known or probable human carcinogens [5].

A 2023 editorial in the National Library of Medicine put it bluntly: “formaldehyde and aromatic hydrocarbons like toluene and benzopyrene may be released in large quantities from commonly available scented candles, especially the less expensive ones made from paraffin wax.” The same editorial documented a case in which a 66-year-old woman developed exogenous lipoid pneumonia, a serious lung condition from inhaling vaporised paraffin from burning candles [6].

IQAir noted that the ultrafine soot particles from paraffin candles are “similar to diesel exhaust in both their size and composition.” They penetrate deep into the lungs and are absorbed into the bloodstream [7].

It’s Not Just About the Wax

In 2024, CNN conducted a deep-dive investigation into candle science and uncovered something surprising: when researchers tested a lit strawberry-scented candle, it emitted formaldehyde at 2,098 parts per billion, more than five times the upper limit of what’s considered acceptable. But when they tested a lit unscented candle? It had the lowest emissions of all [8].

This suggests something counterintuitive: the fragrance might be a bigger problem than the wax.

Most scented candles use synthetic fragrances and dyes that release VOCs, including formaldehyde, limonene, petroleum distillates, and esters, even at room temperature, before the candle is lit [7]. Some synthetic fragrances also contain phthalates, chemicals linked to hormonal disruption.

Dr. Sarah Evans, assistant professor of environmental medicine at Mount Sinai’s Icahn School of Medicine, told CNN: “anything that is burned emits harmful particulates or chemicals.” Even essential-oil-based candles aren’t automatically off the hook, because the heat of combustion can alter the chemical composition of the oils themselves [8].

If you switch from a paraffin candle to a soy candle but buy one that’s heavily fragranced with synthetic scents, you may not be reducing your exposure as much as you think. The fragrance load is an independent and potentially larger risk factor than the wax type.

What Does This Actually Do to Your Body?

The immediate effects of candle pollution are the best-studied and most widely reported. The 2023 PMC editorial catalogued the most common complaints from scented candle exposure [6]:

A 2017 University of Copenhagen study found that particles from burning candles caused more lung damage in mice than researchers anticipated [9]. A Danish field study found that burning a candle for just over two hours contributed to two-thirds of all ultrafine particles measured in indoor air, meaning candles can dominate a room’s air pollution profile [8].

Are Natural Candles Actually Better?

The short answer is yes, in general, but there are important caveats.

A 2025 experimental study directly compared soy and paraffin candles and found a dramatic difference. Soy candles produced peak PM₂.₅ at ≤88 µg/m³, while paraffin candles peaked at 3,361 µg/m³, a roughly 38-fold difference [10]. A 2002 study in the Journal of the American Oil Chemists’ Society similarly found that soy and beeswax burned more slowly and produced less soot than paraffin [7].

While research on how humidity specifically interacts with candle emissions is still limited, what we do know is that high humidity can affect how particles and VOCs behave in enclosed spaces. In a hot, humid Hong Kong summer when windows are closed and air conditioners are running, candle pollutants may linger longer and interact with other indoor contaminants in ways that are not yet fully understood.

Are there regulations?

This is something every consumer should know: there are no regulations that require full labeling of candle contents, and no third-party testing to check manufacturers’ claims [8].

Words like “natural,” “clean-burning,” “non-toxic,” and “pure” on candle packaging are mostly unregulated marketing terms, not certified standards. A company could label a paraffin candle with synthetic fragrance and a zinc-core wick as “non-toxic,” and no one would stop them.

The one notable exception: the U.S. Consumer Product Safety Commission banned lead-core wicks in 2003 after determining they could cause lead poisoning in children. But zinc- and tin-core wicks, the replacements, can still release trace amounts of heavy metals when burned [7].

So… Should You Throw Out Your Candles?

Not necessarily. But it might be a good idea to change how you use them.

The goal isn’t to live in a scent-free bubble. It’s about making informed choices about what you breathe. Here is what the evidence supports:

If You Want to Keep Burning Candles

If You Want the Ambiance Without the Combustion

• Essential oil diffusers spread fragrance using water vapor instead of burning, so they avoid most particulate matter and combustion by-products [7].
• Electric wax warmers melt scented wax without a flame, dramatically reducing emissions
• Simmer pots — a pot of water with cinnamon sticks, cloves, and citrus peels on the stove — create natural fragrance with zero combustion pollutants
• Indoor plants like areca palm and snake plant naturally filter air while adding greenery

If You Want to Relax Without Candles at All

It’s ironic that the stress relief people look for in candles—the calm, mindfulness, and sensory ritual—can also come from music, meditation, deep breathing, or a warm bath in clean air. A candle is just one option, not the only one.

Hong Kong’s Local Candle Scene: What to Look For

Hong Kong has a thriving candle culture, from luxury imports at Lane Crawford to artisanal local makers. Local brands like BeCandle (Sai Kung), Carroll & Chan, The Wax Can, Lapzuk, and Scent Clinic have built loyal followings, while eco-conscious shops like Slowood carry sustainable options [11][12].

But as we’ve seen, the words “natural” and “clean-burning” on the label don’t guarantee anything; there’s no regulation backing those claims in Hong Kong. When shopping locally, ask directly:

• What wax is used? (Look for 100% soy, beeswax, or coconut — not “wax blends” which may contain paraffin)
• Is the fragrance from essential oils or synthetic fragrance oils?
• Does the wick contain metal? (Ask for cotton or wood wicks)
• Is the product phthalate-free?

Local artisans who make small-batch candles are often more transparent about their ingredients than mass-market brands. Don’t be afraid to ask; the best Hong Kong candle makers will happily tell you exactly what’s in their products.

The Bottom Line

Scented candles won’t give you cancer overnight, but they aren’t as harmless as they seem. Every time you light one, you add measurable pollutants to your home’s air. Some of these are known carcinogens, and all are avoidable.

The science tells us three things clearly:

1. Candles release real pollutants — VOCs and particulate matter — at levels that can exceed air quality guidelines.
2. Paraffin and synthetic fragrances are the biggest culprits, and the two should be evaluated separately, not lumped together.
3. The long-term cancer risk remains unproven in humans, even though the chemical evidence is concerning.

So enjoy your candles, but do so wisely. Open a window. Choose cleaner wax. Use fewer synthetic fragrances. And sometimes, just dim the lights and breathe.

Truly clean air, after all, smells like nothing at all.

References

1.Yun, H. et al. (2025). Impact of scented candle use on indoor air quality and airborne microbiome. Nature Scientific Reports. Link

2.U.S. EPA (2001). Candles and Incense as Potential Sources of Indoor Air Pollution. Link

3.[E] Environmental Protection Department, HKSAR Government. Guidance Notes for the Management of Indoor Air Quality in Offices and Public Places. Link

4.Malibu Apothecary. Is Paraffin Wax Toxic? Health Risks of Burning Paraffin Candles. Link

5.Massoudi, R. & Hamidi, A. (2009). Emission products of petroleum-based candles. South Carolina State University, ACS symposium presentation. Link

6.Nazir, Z. (2023). The unknown risks of scented candles! What science has to say: an editorial. National Library of Medicine / PMC. Link

7.IQAir (2023). The hidden dangers of scented candles. Link

8.CNN (2024). Are scented candles bad for you? What the research says. Link

9.University of Birmingham (2017). Indoor Air Quality: The truth about candles. Link

10ResearchGate (2025). Indoor Air Quality Implications of Soy Wax versus Paraffin Wax Candles: An Experimental Study. Link

11.Time Out Hong Kong. Best places to buy candles in Hong Kong. Link

12.Sassy Hong Kong. Where to Buy Scented Candles in Hong Kong. Link