What's Really in the Air When You Burn a Scented Candle?

                                                  Figure 1. Scented candles in glass holders. From www.carolinacool.com

    What's Really in the Air When You Burn a        Scented Candle?

                                       Tayren N. Ben-Abraham, MPH, MSc., M.A., M.A.

                        

                                            Figure 2. Scented candles, when they are lit, release various chemical into the air. This figure shows an example of linalool responsible for the lavender scent on the left, limonene on the top right responsible for the scent of lemons, and on the bottom right an unspecified ring structure representing volatile organic compounds and other chemicals. From: Sobe Staff (2025).

Imagine walking into your home after a long day. You light a lavender or vanilla candle, and within minutes your dwelling smells warm and inviting. For many people, scented candles are associated with relaxation, comfort, and a cozy atmosphere. It is easy to assume that the pleasant fragrance is all that is being released into the air. The reality is more complex.

When a candle burns, it produces much more than light and fragrance. The flame creates a mixture of gases, microscopic particles, and fragrance chemicals that become part of the air you breathe. Most healthy adults are unlikely to become seriously ill from occasionally burning a candle in a well-ventilated room. However, understanding what is released into the air can help you make informed choices, especially if you have asthma, allergies, other respiratory conditions, or spend much of your time indoors.

A Candle Is More Than Just Wax

            Although candles appear simple, they contain several components that contribute to indoor air pollution when burned such as the wax, a wick, fragrance chemicals, and some candles may contain dyes or even decorative additives (Singha & Singha, 2024). Here is a diagram showing the anatomy of a candle.

                                                Figure 3. Candle Anatomy Diagram. From Good Smells Inc.

When a candle is lit, the wax melts and is drawn up the wick by capillary action (Frilliciardi et al., 2026). Capillary action is the movement of a liquid through tiny spaces because its molecules stick to surfaces and to each other (Filliciardi et al., 2026). One way to think of capillary action is to imagine it this way: Imagine a line of people holding hands. If the first person climbs a small step and pulls the others along, the whole line moves upward. Water molecules and other liquids can do something similar in very small spaces. The heat vaporizes the liquid wax, and these vapors burn in the flame to produce light and heat (Elisabet & Kurniawan, 2022). At the same time, fragrance ingredients evaporate into the surrounding air, where they can be inhaled (Al-Khathlan et al., 2023). As a result, you are breathing far more than the pleasant scent itself. I have provided an illustration below showing the process of a burning candle and the chemistry behind it at the end of the post. For now, let’s talk about the chemicals and other things candles put into the air.

Tiny Particles You Can't See

One of the primary pollutants released during candle burning is particulate matter, especially particles smaller than 2.5 micrometers in diameter, known as PM2.5 (Mostafa et al., 2021). The PM means particulate matter and the 2.5 means it is 2.5 microns. A micron is one-millionth of a meter, so a 2.5-micron particle could fit across the width of one human hair 20 to 40 times. These particles are so small that they can bypass many of the body's natural defenses, travel deep into the lungs, and in some cases enter the bloodstream (Thangavel et al., 2022).

Figure 4. Relative sizes of PM10, a red blood cell, PM 2.5, a bacillus bacteria, and a coronavirus virion (virus particle). From Mayairgroup.com

 

Long-term exposure to elevated PM2.5 from many different sources, including wildfire smoke, vehicle exhaust, wood-burning stoves, and other forms of combustion, has been associated with a variety of health outcomes including death (Sangkham et al., 2024). The diagram below shows a limited selection of common health outcomes from PM2.5.

Figure 5. Particulate matter, when inhaled for short periods of time or long periods of time have distinct health outcomes.

A single candle generally produces far less particulate matter than major outdoor pollution sources. However, burning several candles simultaneously or burning candles for many hours in a small, poorly ventilated room can noticeably increase indoor particle concentrations (World Health Organization, 2024). Over time, pollutants accumulate as well as the risk for serious illness. Even with flame-free candles, the same pollutants are produced and can equally as harmful to our health (Patra et al., 2025). According to Patra et al., (2025), even as flameless candles and melting scented wax products are promoted as being non-toxic, that claim is actually false.

Figure 6. Cardiovascular effects are common with particulate matter exposure. These exposures can affect organs and body systems such as the lungs, heart, the immune system, and the brain which all rely on blood flow. These organs are affected by these organs and systems to cause the diseases presented at the bottom of the graphic.

Volatile Organic Compounds (VOCs): Invisible Chemicals in the Air

Another important group of chemicals released during candle burning is volatile organic compounds (VOCs). VOCs are chemicals that readily evaporate into a gas that mixes with the air at room temperature, which is why scented candles have a noticeable aroma even before they are lit (US EPA, 2019). Below are some flavors and scents we encounter in candles and foods that are volatile organic compounds. These chemicals occur naturally and can also be manmade.

Figure 7. A visual showing fragrance molecules, which are volatile organic compounds, that leave a candle flame and entering indoor air. From Instagram.

 

So, if you are wondering how we smell these lovely fragrances and how we inhale particulate matter at the same time, this is how it happens. When a candle is burning, fragrance molecules released from the melted wax and fragrance oils disperse through the air (Thimmapuram, 2024). Some of these molecules enter a person's nose, where they bind to olfactory receptors in the nasal cavity (Chen, 2026). These receptors transmit signals through the olfactory nerve to the brain, allowing the person to perceive and identify the scent (Chen, 2026).

At the same time, the heat from the flame releases additional fragrance ingredients into the air, while combustion produces a mixture of gases and particles (Dasari et al., 2025). Depending on the candle's wax composition, fragrance formulation, wick material, and burning conditions, volatile organic compounds (VOCs) released into indoor air (Hasan et al., 2025). Not every candle emits all of these compounds, and the types and concentrations can vary considerably between products. Some VOCs are directly released from fragrance oils, while others may be generated as combustion byproducts when wax and fragrance compounds are heated and burned (Hasan et al., 2025).

Figure 8 Toxicology Exposure Principle. We can determine the toxicity of a chemical by the chemical itself, how much of the chemical we take in, how it enters our body, and the duration of exposure. Toxicity depends on this principle, not whether the chemical is natural or synthetic.

When Indoor Chemistry Changes the Air

The chemistry of indoor air does not stop once fragrance chemicals leave the candle, they actually persist for some time. Many homes also contain small amounts of ozone that drift indoors from outdoor air (Nazaroff & Weschler, 2022). Some fragrance chemicals react with ozone after they are released, producing new pollutants (Wang et al., 2023).  This can introduce new health risks. Among these secondary pollutants are formaldehyde, ultrafine particles, and other oxygen-containing compounds (Richard et al., 2024). Although scientists continue to study how much these reactions contribute to everyday indoor exposure, they illustrate that indoor air is chemically active rather than static. What is known is that these chemicals can negatively impact human health.

What About Paraffin Wax? And other waxes?

Paraffin candles are often criticized because paraffin wax is derived from petroleum (Krendlinger & Wolfmeier, 2022). While this sounds concerning, the science is more nuanced. When a candle burns efficiently, paraffin wax is converted primarily into carbon dioxide and water, along with relatively small amounts of soot and other combustion byproducts (Wang, 2023). The less efficiently the candle burns, the more soot that is produced.

What about other types of candle waxes such as soy, beeswax, and others? Soy wax is a plant-derived alternative to paraffin that may produce less soot under proper burning conditions, but emissions can still occur from fragrance chemicals, wick materials, additives, and incomplete combustion (Rezaei & Wang, 2002). So, you get more soot and more pollution output from soy candles. Beeswax candles often burn with a cleaner flame and may generate fewer visible particles than some other waxes, but they still release combustion products, including fine particles and VOCs, especially when burned in poorly ventilated spaces (Zhao et al., 2025). Other plant-based waxes may have favorable burning characteristics, but limited independent research and variations in formulations make it difficult to predict their effects on indoor air quality (Singha & Singha, 2024).

Soot: More Than a Black Stain

If you have ever noticed black residue on a candle jar, ceiling, or nearby wall, you have seen soot. Soot is made up of thousands of chemicals yet consists primarily of tiny carbon particles produced during incomplete combustion (Klaassen, 2019). Soot is formed during incomplete combustion of an organic fuel such as the wax from your candle or the gas from your gas stove (Liu & Consalvi, 2023). Keeping the wick trimmed to approximately one-quarter inch before each use can help reduce soot formation.

Simple Ways to Reduce Exposure

If you enjoy scented candles, you do not necessarily need to stop using them. Simple habits can reduce exposure while allowing occasional enjoyment. Here are some simple tips:

·       Open a window and keep the space well ventilated.

·       Trim the wick.

·       Reduce the number of candles if you like to burn multiple candles.

·       Avoid smoke in public, outdoors, and in your home. Multiple exposures increase your risk.

·       Limit the time you burn your candles to reduce your risk.

The Bottom Line

Scented candles create a pleasant atmosphere, but they also change the chemistry of the air inside your home. Burning candles releases fine particles, combustion gases, and volatile organic compounds, while some fragrance chemicals can react with indoor ozone to form additional pollutants. For most healthy adults, occasional candle use in a well-ventilated room is unlikely to pose a significant health risk. However, repeated exposure in enclosed spaces can increase indoor air pollution, particularly for people with asthma, respiratory disease, or fragrance sensitivities. The next time you light your favorite scented candle, remember that you are doing more than filling the room with fragrance - you are also changing the chemistry of the air you breathe.

 

Encore…

Every once in a while, there will be an encore to the lesson. In this encore, here is a diagram made by a high school student to show the chemistry of how candles burn. Remember that chemistry is the science of materials and how they interact. Here is the graphic. Kudos to the student, they did an excellent job of taking detailed notes.

References

Al-Khathlan, N., Basuwaidan, M., Al Yami, S., Al-Saif, F., Al-Fareed, S., & Ansari, K. (2023).

Extent of exposure to scented candles and prevalence of respiratory and non-respiratory

symptoms amongst young university students. BMC Public Health, 23(1), 80.

Basith, S., Manavalan, B., Sin, T. H., Park, C. B., Lee, W.-S., Kim, J., & Lee, G. (2022).

Biological pathways associated with particulate matter and cardiovascular disease

[Journal Article]. In Journal article . https://www.mdpi.com/2079-4991/12/15/2656

Chen, J. (2026). Nasal Cavity and Olfactory Receptors. Food Oral Processing: Fundamentals of

Eating and Sensory Perception, 1, 49-64.

Dasari, S., Kakara, M., Maloth, S., Karthikeyan, S., & Katam, K. (2025). Inhalation Risk

Assessment of Formaldehyde and PM2. 5 from Fragrance Product Emissions in Indoor

Environments. International Journal of Environmental Pollution and Remediation, 13, 47-57.

Elisabet, Y., & Kurniawan, C. (2022). Understanding the Difference Between Chemical Changes

and Physical Changes. Indonesian Journal of Chemical Science and Technology, 5(1),

51-57.

Frallicciardi, P., D’Acunto, I., & Di Bartolomeo, A. (2026). A sensor-based study of the candle-

under-glass experiment. European Journal of Physics, 47(3), 035805.

Hasan, A. B. M. R., Pillai, K. M., Ihrke, M., Ali, M. S., & Mirza, S. (2025). A next-generation

device for spreading volatiles substances into room air: Study of parameters affecting

efficient dispersion. International Journal of Heat and Mass Transfer, 241, 126709.

Klaassen, C. D. (2019). Casarett and Doull’s Toxicology : The Basic Science of Poisons (9th

ed.). McGraw-Hill Education.

Krendlinger, E. J., & Wolfmeier, U. H. (2022). Natural and Synthetic Waxes: Origin,

Production, Technology, and Applications. John Wiley & Sons.

Liu, F., & Consalvi, J. L. (2023). Carbonaceous particles in flames and fires. In Light,

Plasmonics and Particles (pp. 371-391). Elsevier.

Mostafa, M. Y. A., Khalaf, H. N. B., & Zhukovsky, M. V. (2021). Dynamic of particulate matter

for quotidian aerosol sources in indoor air. Atmosphere, 12(12), 1682.

Nazaroff, W. W., & Weschler, C. J. (2022). Indoor ozone: Concentrations and influencing

factors. Indoor air, 32(1), e12942.

Patra, S. S., Jiang, J., Liu, J., Steiner, G., Jung, N., & Boor, B. E. (2025). Flame-Free Candles

Are Not Pollution-Free: Scented Wax Melts as a Significant Source of Atmospheric

Nanoparticles. Environmental Science & Technology Letters, 12(2), 175–182.

https://doi.org/10.1021/acs.estlett.4c00986

Rezaei, K., Wang, T., & Johnson, L. A. (2002). Combustion characteristics of candles made

from hydrogenated soybean oil. Journal of the American Oil Chemists” Society, 79(8),

803–808. https://doi.org/10.1007/s11746-002-0562-y

Richard, G., Hait, M., & Ibrahim, M. (2024). Emerging chemical air contaminants and their

associated human health effects. In Air Pollutants in the Context of One Health:

Fundamentals, Sources, and Impacts (pp. 187-210). Cham: Springer Nature Switzerland.

Sangkham, S., Phairuang, W., Sherchan, S. P., Pansakun, N., Munkong, N., Sarndhong, K.,

Islam, Md. A., & Sakunkoo, P. (2024). An update on adverse health effects from

exposure to PM2.5 [Review of An update on adverse health effects from exposure to

PM2.5]. Environmental Advances, 18( 100603), 100603.

https://doi.org/10.1016/j.envadv.2024.100603

Singha, R., & Singha, S. (2024). Indoor Air Pollution: Causes, Effects, And Solutions. Effects,

And Solutions (November 25, 2024).

Sobe Staff. (2025, December 2). The SOBE World Co. The SOBE World Co.

https://www.sobeworldco.com/blogs/news/%E2%9C%A8-light-up-your-mood-the-science-of-scent-and-the-soul-of-our-soy-candles

Thangavel, P., Park, D., & Lee, Y. C. (2022). Recent insights into particulate matter (PM2. 5)-

mediated toxicity in humans: an overview. International journal of environmental

research and public health, 19(12), 7511.

Thimmapuram, U. K. R. (2024). Preparation And Evaluation Of Polyherbal Scented Candle

Using Volatile Oils Extracted By Enfleurage Method: Evaluation Of Polyherbal Scented Candle. INDONESIAN JOURNAL OF HEALTH SCIENCES RESEARCH AND DEVELOPMENT (IJHSRD), 6(1), 38-48.

Wang, D., Xing, Y., Li, J., Dong, F., Cheng, H., He, Z., ... & Ma, J. (2023). Degradation of odor

compounds in drinking water by ozone and ozone-based advanced oxidation processes: a

review. ACS ES&T Water, 3(11), 3452-3473.

Wang, C. (2023, February 14). Candles: What do they emit when lit? [Review of Candles: What

do they emit when lit?]. Office for Science and Society.

https://www.mcgill.ca/oss/article/student-contributors-you-asked-general-

science/candles-what-do-they-emit-when-lit

World Health Organization. (2024, October 16). Household Air Pollution and Health. Who.Int;

World Health Organization: WHO. https://www.who.int/news-room/fact-sheets/detail/household-air-pollution-and-health

Zhao, S. M., Liu, W. X., Miao, Q. Y., Li, J. M., Sun, L. M., & Wu, S. P. (2025). Emissions

characteristics of polycyclic aromatic hydrocarbons, water-soluble heavy metals, and

oxidative potential from indoor non-energy combustion sources. Environmental Science

and Pollution Research, 32(25), 15342-15358.