Is soy cleaner than paraffin, and are candles bad for indoor air?
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No one has shown it either way. No good peer-reviewed study has been published comparing the emissions of soy and paraffin candles, and the study most often quoted against paraffin was never published in a peer-reviewed journal. The most detailed exposure study of scented candles found, by authors from fragrance and consumer-products companies, concluded that under normal use they "do not pose known health risks to the consumer," while a 2025 animal study reported lung effects under heavy, poorly described exposure. What you can control is soot, the visible part of a candle's emissions. This page sets out what each study found and what that means for how you make and describe a candle.
What a burning candle gives off
A candle flame burns the wax vapor drawn up the wick. Complete combustion produces mainly carbon dioxide and water; incomplete combustion produces soot (fine carbon particles) and other byproducts, and a scented candle also releases fragrance compounds, which is the point of it. The studies below measured three groups of emissions: volatile organic compounds (VOCs, which evaporate readily at room temperature), semi-volatile organic compounds (SVOCs) and particulate matter (fine particles in the air, including soot).
The studies, and what each one can support
| Study | Who did it | What it measured | What it found | Limits |
|---|---|---|---|---|
| Petry et al., Regulatory Toxicology and Pharmacology, 2014 [1] | Authors listed with ToxMinds, the Research Institute for Fragrance Materials (RIFM), SC Johnson, Firmenich, Procter & Gamble and Reckitt Benckiser [2] | VOC, SVOC and particulate emissions from scented candles in small and large controlled chambers; indoor concentrations then modeled for a standard EU dwelling and compared with air quality guidelines and toxicity thresholds | Under normal use, scented candles "do not pose known health risks to the consumer" | Industry-affiliated authors. Modeled exposure, not measured in homes. Covers scented candles, not a comparison of waxes |
| Mohamed et al., Frontiers in Public Health, 2025 [3] | University and hospital researchers in Egypt and Saudi Arabia | Rats exposed to an unscented or a scented commercial candle for 1, 3 or 6 hours a day, 5 days a week for 8 weeks in a sealed 3 x 3 x 2.8 m room; VOCs identified by GC-MS | Inflammation markers, oxidative stress and lung tissue damage rose with exposure time, more with the scented candle | Wax type, brand and fragrance not named. No room concentrations or emission rates reported, so the dose cannot be compared with home use. Many toxicity flags were computer predictions |
| Systematic review of PAHs from scented candles, Journal of Research in Environmental Health [4] | Three authors at Tehran University of Medical Sciences | Literature on polycyclic aromatic hydrocarbons (PAHs) from scented candles: 1,297 records screened, 11 studies included | Recommends "cleaner alternatives (e.g., soy or beeswax candles)," shorter burns, natural wicks and ventilation, and calls for more research | The review's published summary reports no comparative data between waxes to support the soy or beeswax recommendation |
| South Carolina State University, 2009 (as reported) | University researchers | Reported toluene and other chemicals from paraffin candles | Widely cited against paraffin | According to a supplier that looked into it, "never published in any peer-reviewed journals" and no longer on the university's website [5]. It cannot be checked |
Read together, the evidence supports three statements. Scented candle emissions, modeled for normal home use, fell below the guideline values one industry-funded team compared them against. Heavy exposure in a sealed room produced harm in rats, at doses nobody has related to how people burn candles. And no study read here compares soy with paraffin, or either with beeswax, under the same conditions.
What has not been studied
These questions come up repeatedly from makers and customers and have no good peer-reviewed answer:
- Soy versus paraffin versus beeswax emissions measured side by side, with the same wick, fragrance and burn conditions.
- Coconut and other blends, which combine vegetable waxes with paraffin.
- The effect of fragrance load on emissions in ordinary home candles.
- Real homes. The chamber study modeled a dwelling; nobody has published a large study measuring candle emissions in the rooms where people burn them.
- Independent replication of the main industry study by authors without fragrance or consumer-products affiliations.
The honest answer to "is soy cleaner?" is that the question has not been tested well enough to say.
Soot is the part you can see and control
Whatever the wax, a candle that smokes is burning incompletely, and that is something you can observe, measure and fix. CPSC lists ASTM F2326, the standard test method for collecting and analyzing visible emissions from candles as they burn, among the six ASTM candle standards it lists for businesses [6]. The National Candle Association's consumer advice is to trim the wick to 1/4 inch before each use, which it says helps limit high flames and soot, to avoid drafts from open windows, fans and vents, and to burn candles in well-ventilated rooms [7].
For a maker, that means soot is a wick and formula question:
- Measure it in your burn test. How to check for soot and the smoke limits one retailer uses are on measuring soot and smoke in a test.
- Fix it when a candle smokes. Causes in order of likelihood are on stopping a candle from sooting.
- Tell customers how to burn it: trimming, drafts and burn time belong on burn instructions to give customers.
What this means for your label
Because no good comparative evidence exists, claims that a wax is "cleaner burning," "non-toxic," "healthier" or "soot-free" have nothing behind them that you could show a regulator, a retailer or a customer. The federal rules on environmental and health claims, including when a health claim turns a product into something regulated differently, are on what you can claim about your candle. Describe what the wax is and how to burn the candle well.
If you or a customer notice irritation, headaches or breathing trouble while a candle burns, put it out and ventilate the room, and seek medical advice for symptoms that continue.
The claims rules come next
If you are writing a label or a product description, go to what you can claim about your candle before you print anything. If you are still choosing a wax, the physical differences that do have sources (melt point, fragrance load, cure, frosting) are compared on choosing a candle wax.
References
- Petry T, Vitale D, Joachim FJ, Smith B, Cruse L, Mascarenhas R, Schneider S, Singal M., Human health risk evaluation of selected VOC, SVOC and particulate emissions from scented candles, Regulatory Toxicology and Pharmacology 69(1):55-70, 2014. https://doi.org/10.1016/j.yrtph.2014.02.010
- Pherobase, literature record for Petry et al. 2014 with abstract and author affiliations, read October 22, 2026. https://pherobase.com/literature/data/details/B/22611
- Mohamed MS, Omran AME, Obidan A, et al., Toxicological evaluation of volatile organic compounds emitted from scented candles: in silico ADMET profiling, oxidative stress, inflammation, and lung injury in rats, Frontiers in Public Health 13:1678549, September 18, 2025. https://pmc.ncbi.nlm.nih.gov/articles/PMC12488666
- Journal of Research in Environmental Health, Investigating the Impact of Scented Candles on the Emission of Polycyclic Aromatic Hydrocarbons (PAHs) and Their Health Implications: A Systematic Review, read October 22, 2026. https://jreh.mums.ac.ir/article_26106_en.html
- Village Craft & Candle, Soy Wax vs Paraffin Wax, Erin Parsons, October 23, 2021. https://villagecraftandcandle.com/blogs/news/soy-wax-vs-paraffin-wax
- U.S. Consumer Product Safety Commission, Candles Business Guidance, undated, read October 22, 2026. https://www.cpsc.gov/Business--Manufacturing/Business-Education/Business-Guidance/Candles
- National Candle Association, Candle Safety Tips, modified August 12, 2025. https://candles.org/candle-safety/
