Odours can alter our mental and physical well-being. But could a burning candle also be a secret killer?

An aroma in the air

Ancient Egyptians often get credited for the invention of scented candles. However, we do not know their exact origins. There is some evidence that the first candles were made from whale fat in China, during the Qin Dynasty (221- 206 BC), or from a residue of boiling cinnamon in India, around the same period.

From a physical point of view, candles self-feed themselves. Take, for instance, a cylindrical candle with a cotton wick inside. When the candle is lit, the overheated air melts the wax around it. The wax rises along with the wick towards the flame and mixes with the air, releasing aromas. Molecules from candles form a combustible gas, which is then burned by the flames.

For that reason, candles were then used for illumination and sometimes for heating. Nowadays, however, they are mostly used for decoration and relaxation. And they have become popular again. Only in 2018, over 700 thousand tons of candles were consumed in the EU.

Wolf in sheep’s clothing

Recently, scent marketing has also become more and more common: shops, cafes, restaurants try to attract us with pleasant odours. We are constantly surrounded by a sea of ​​aromas. But have you ever wondered what chemicals are hidden behind our favourite smells?

Unfortunately, scented candles contain compounds that might be toxic to us. Harmful particles invade not only our indoor airs; they also escape our houses, react with other pollutants, and form ozone. Ozone is beneficial in upper portions of the atmosphere; however, in the lower ones, it is highly toxic and reactive, triggering asthma attacks and eye and throat inflammation. 

Wax composition and the candles’ scent are two separate topics. The least toxic candles are made from natural ingredients, such as beeswax —the oldest raw material for candle making— and soybean wax. In contrast, most scented candles are based on paraffin wax prepared from petroleum, coal, or shale oil. Additives, such as pigments or aromas, modify these candles so when they melt, they emit harmful toxic compounds.

Dangerous ingredients in a romantic atmosphere

One of the components of candles is formaldehyde, a well-known carcinogen, possibly linked to leukaemia. However, its toxic effects are not only limited to cancers. Even in low concentration, formaldehyde can cause eye and upper airway irritation.

There are also other chemicals that are released from scent candles. Naphthalene causes inflammation, leads to DNA damage, and is a potential carcinogen. Prolonged exposure to it may cause serious health problems due to this compound’s toxicity. Toluene is found both in candles and in nail-polish. It affects the central nervous system and leads to permanent brain toxicity. It also affects lungs, kidneys, eyes, and skin, causing inflammation, headache, nausea, dizziness, or even loss of coordination. Anthracene can cause inflammation of the gastrointestinal tract, skin problems like inflammation, and skin pigment loss, while its fumes may lead to breathing problems or cough. This compound is also suspected to be a carcinogen.

Scented candles emit chemicals such as benzene, methacroleine, toluene and anthracene.
Fig.1 Chemicals released from scented candles

Moreover, paraffin wax also produces much more soot than its natural alternatives. It is full of particulate matter, like PM2.5, which pollutes the indoor air, especially when many candles are lit at the same time. Soot is responsible for countless asthma attacks, heart diseases and sometimes even cancer, mostly because of its power to induce mutations in DNA. Although its effects are highly dependent on the amount of exposure, it is still important to minimize our contact with carcinogens for our safety.

But what about fragrances in scented products? When they burn, fragrances emit volatile organic compounds (VOC) that might be hazardous or toxic. There are over 100 chemicals in air scenting products, which may cause respiratory, dermatological, and neurological problems. The same concerns natural fragrances based on terpenes like α-pinene and β-pinene from pine, d-limonene from citruses, linalool from lavender or myrcene from hops. They may undergo degradation to toxic and cancerogenic compounds like benzene and methacrolein. Benzene is a well-known carcinogen that is also toxic for the nervous, respiratory, and cardiac system, while methacrolein also affects many organs when it is inhaled, consumed, or absorbed by the skin.

A less fragrant but healthier alternative

It sounds quite scary that there are so many toxic compounds in candles. This does not mean that we should not light candles at important religious ceremonies, or romantic evenings. A remedy for the harmful effects of candles is just choosing products that are based on natural compounds – which are healthier alternatives to synthetic wax – such as beeswax, soybean wax or other plant-based waxes. Burning soybean waxes release less soot than paraffin-based ones, which makes it a safer alternative. Additionally, soy wax burns slower than paraffin and is fully biodegradable.

Unlike natural candles, scented candles are made of synthetic wax, which release VOCs,
Fig. 2 Natural candles vs synthetic candles

Scents, however, are a completely different story. Whenever you burn in a candle, it emits volatile compounds. Ideally, the burning process should lead only to the emission of water and carbon dioxide. Yet, with candles, many more chemicals are released into the air. This is the reason why safe candles do not emit any scent.

Scented candles release unwanted chemicals into the air, so when we are frequently exposed to them, we inhale dangerous pollutants that increase the risks of cancer, allergies, and other health problems. In general, the use of candles in closed rooms, especially without proper ventilation, should be avoided. Candles should be lit in the open space.

This article is a joint work of Zuzanna Kozłowska (Faculty of Chemistry, University of Warsaw), Agnieszka Pregowska (Institute of Fundamental Technology Research), and Magdalena Osial (Faculty of Chemistry, University of Warsaw) as a part of Science Embassy project.

Figures – Magdalena Osial

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Agnieszka Pregowska is a scientist from the Institute of Fundamental Technological Research Polish Academy of Sciences. Her research is focused on biomedical signal processing, neuroinformatics, and the application of Augmented and Mixed Realities in medicine. She is an engineer working on various signal types. She collaborates with scientists from medicine, biophysics, bioengineering, computer science, statistics, and informatics to provide the inside to personalized medical diagnostics. Discovering the secrets of the human brain is her passion. She enjoys traveling, long-distance cycling, dancing, and motorization.


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