If you've been reading about candles online, you've probably encountered warnings about toxic emissions, debates about paraffin versus soy wax, and concerns about indoor air quality. It can be confusing to sort through all the claims. Let's break down what the science actually says when it comes to candle quality and safety.
To understand the combustion process we're discussing here, check out our companion post: The Science Behind Your Candle's Glow: How Candles Burn
The Chemistry of Combustion: Not Always Perfect
When we discussed how candles burn in our companion article, we explained that wax hydrocarbons ideally break down into carbon dioxide and water. But the reality is more nuanced. In the oxygen-poor center of the flame, the combustion process can create intermediate compounds during what's called pyrolysis, the thermochemical decomposition of carbon molecules at high temperatures in the absence of oxygen.
Some of these fragments are aromatic hydrocarbons. You may have heard the names of some these compounds, such as benzene (C₆H₆) and toluene (C₇H₈). These form because when carbon-carbon bonds break under high heat with limited oxygen, the carbon atoms often rearrange into stable ring structures rather than breaking down completely.
Understanding Candle Emissions and Safety
It's worth addressing a common concern: some of these intermediate compounds, particularly benzene and toluene, are toxic substances. Benzene is a known carcinogen, and toluene is a neurotoxin that can cause headaches and dizziness at high concentrations. This understandably raises questions about candle safety.
However, context and concentration matter enormously. The amounts of these compounds released by a well-made candle burning under normal conditions are quite small, typically far below established safety thresholds.
Beyond "Non-Toxic" Marketing Claims
You've probably seen candles marketed as "non-toxic" or "clean-burning." These terms sound reassuring, but they don't actually have standardized definitions in the candle industry. There's no regulatory body that certifies a candle as non-toxic, and no agreed-upon threshold or even definitions for what qualifies as either “non-toxic” or “clean-burning”.
The "non-toxic candle" phenomenon has an interesting origin story—one that traces back to a single 2009 conference presentation that was never peer-reviewed but fundamentally changed how the entire industry markets candles. The study found certain compounds in paraffin candles. The media translated this to "paraffin is toxic," and suddenly "non-toxic" became the most valuable phrase in candle marketing. Read the full story: The "Non-Toxic Candle" Myth: How One Study Changed an Industry
Why Some Candles Produce More Unwanted Compounds
It is in the very nature of burning a candle that intermediate compounds will be produced, and some will end up being released as unintended emissions. The composition and quantity of these emissions depend on a number of factors, including:
Wick size and material: A well-designed candle with an appropriately sized wick maintains efficient combustion, minimizing incomplete burning and emissions of intermediate molecules or particles. An oversized wick creates a larger flame that consumes oxygen faster than it can be replenished, leading to incomplete combustion. When combustion is incomplete, more intermediate products will be released.
This is why proper wick sizing is crucial for candle quality and why we rigorously test each and every candle model we sell to ensure we are using the right wick for each vessel. (Disclaimer: candles can burn differently in different environments, particularly at different ambient room temperatures. Therefore, we cannot guarantee that our candles will burn the same every home as they do in our testing environment.)
Additives and fragrances: Fragrances introduce additional chemicals into the combustion process, many of which break down into volatile organic compounds (VOCs) that contribute to indoor air quality concerns. These additives are a far more significant source of indoor air quality concerns than the base wax itself [1]. By eliminating these additives entirely, unscented candles significantly reduce the variety and quantity of compounds released into your home.
The effects of dyes are less well understood. Most research on candle safety has focused on wax type and fragrance compounds, with dyes receiving relatively little attention in the scientific literature. However, the amount of dye added is substantially lower than the amount of fragrance that is usually added to scented candles. While in scented candles fragrances may make up from 3-12% of the final weight of a candle, the drops of liquid dye I put in a candle is on the order of 0.05% of the weight.
Wax quality and composition: Wax quality and purity matter more than wax type when it comes to emissions. Well-refined, high-purity waxes—whether paraffin, soy, beeswax, or other sources—burn more cleanly and predictably than lower-grade alternatives [2]. The refinement process removes impurities and creates consistent molecular structures that combust more completely, reducing the formation of unwanted byproducts.
The Unscented Advantage
When you compare candle emissions, the presence or absence of fragrance makes a significant difference. Most fragrances used for candle production, even by small candle makers, are complex mixtures of chemicals. When these compounds enter the combustion zone, they break down in unpredictable ways, adding to the variety of substances released into your home. Unscented candles eliminate this entire category of potential emissions. The flame only needs to deal with the wax itself. The simpler composition of fragrance-free candles results in cleaner, more predictable combustion.
What you can do to lower candle emissions
Trim wicks to ¼ inch before each use: Untrimmed wicks can lead to an over-supply of wax to the flame, leading to incomplete combustion and higher emissions.
Burn time and frequency: For both fire safety and emission reduction, candles should not be burned for more than four hours at a time. Make sure the pool of melted wax does not exceed ½ inch in depth. Deep pools of melted wax may deliver more wax to the flame than can be completely oxidized. Also, a candle should be allowed a several hour rest period before burning it again to allow the wax to fully solidify.
Balance ventilation with flame stability: This might seem contradictory, but you want two things at once: general air circulation in the room (so fresh oxygen is available and emissions disperse) and a protected flame (so the flame burns steadily without disruption). Place your candle where the room has good airflow, but not directly in front of a fan, vent, or open window. Think of it as letting the room breathe while keeping the flame still. Good ventilation allows trace compounds to disperse rather than accumulate.
Transparency about ingredients: Look for manufacturers who are open about what's in their candles rather than hiding behind marketing buzzwords. A truly quality candle doesn't need to claim it's "non-toxic" or “clean-burning”. It demonstrates its quality through thoughtful formulation, transparent ingredients, and consistent low-soot burning.
The Bottom Line
By choosing unscented candles made with high-purity wax and proper wicks and burning them responsibly you can enjoy their ambiance with confidence. The warm glow, the peaceful atmosphere, and the simple pleasure of candlelight can all be yours.
You deserve the joy of candlelight!
1. Salthammer, T., Gu, J., Wientzek, S., et. al. (2021). Measurement and evaluation of gaseous and particulate emissions from burning scented and unscented candles. Environment International, 155, 106590. https://doi.org/10.1016/j.envint.2021.106590
2. Derudi, M., Gelosa, S., et. al. (2014). Emission of air pollutants from burning candles with different composition in indoor environments. Environmental Science and Pollution Research, 21(6), 4320–4330. https://doi.org/10.1007/s11356-013-2394-2
Learn more about the fascinating combustion process in our companion post: The Science Behind Your Candle's Glow: How Candles Burn