Dangers of Scented Candles: Why aromatic candles can harm your health

In autumn and winter many of us love the warm glow and pleasant scent of scented candles.  But these candles can be hazardous: they release pollutants that burden our health.  This guide summarises the latest findings on the dangers of scented candles and shows how to use them responsibly and safely.

What pollutants do scented candles release into the air?

Fine dust from scented candles: soot and ultrafine particles

When wax burns it does more than provide light.  It also produces soot and a large amount of fine particles.  Researchers have shown that a single candle emits 53 billion ultrafine particles per hour and that in winter up to 70 percent of the fine‑dust load in indoor spaces can come from candles.  After the flame is blown out the particle counts rise even further because thick soot clouds form.  These particles resemble those from tobacco smoke, which is why experts recommend ventilating well after extinguishing.  A practical test in a 22‑square‑metre room showed that five scented candles increased the fine‑dust levels (PM10 and PM2.5) by 300 percent.

Gases and nitrogen oxides released by scented candles

When wax does not burn completely it releases gases such as carbon monoxide (CO) and nitrogen oxides (NOx).  In one test the CO concentration in room air rose by 85 percent, showing that candles consume oxygen and release carbon monoxide.  The NO₂ level increased from 19 µg/m³ to 62 µg/m³, well above the recommended limit of 40 µg/m³.  Scientists at Purdue University also point out that fragrance compounds can react with ozone and form nanoparticles that penetrate even deeper into the lungs.

VOC from scented candles (volatile organic compounds)

Many candles contain synthetic fragrances derived from petroleum.  When burned these chemicals evaporate and form volatile organic compounds (VOC).  Researchers at the Fraunhofer Institute have found that fresh, floral scented candles release significantly more VOC than unscented candles and that burning them forms formaldehyde and acetaldehyde.  Formaldehyde is classified as carcinogenic.  Limonene fragrances in citrus candles also react with air to form formaldehyde.  In one trial using an air quality monitor, the VOC level doubled within minutes from 29,000 ppb to 60,000 ppb; even after the flame was out it remained 20 percent above the starting value.  A medical report warns that paraffin candles can emit formaldehyde, toluene and benzopyrene.

Heavy metals and dyes in scented candles

Cheap candles can also contain heavy metals.  Germany’s Federal Institute for Risk Assessment (BfR) points out that lead compounds from the wick and nickel and dyes enter the room air when candles are burned.  Lead is particularly harmful to children’s nervous systems and can impair mental development.  Nickel is even classified as carcinogenic.  Consumer advocates also note that leaded candles can harm the brain and nerve development of children.

PAHs and other pollutants from scented candles

When candles burn they produce polycyclic aromatic hydrocarbons (PAHs) such as benzo[a]pyrene and acrolein.  Tests found that these values sometimes reach the limits set by the World Health Organisation.  An American report also notes that cheap candles with artificial fragrances and dyes are made from benzene and toluene derivatives, chemicals suspected of causing bladder cancer.  In one dramatic case a 66‑year‑old woman developed pneumonia after inhaling paraffin fumes.

Health risks from scented candles: possible effects

The mixture of soot, fine dust, gases and VOC can irritate the airways and cause headaches and mucous membrane irritation.  Permanently elevated fine‑dust levels increase the risk of heart and lung diseases, chronic bronchitis and lung cancer.  Formaldehyde and benzene are known carcinogens; the benzene in paraffin is released when burned.  Nitrogen dioxide can worsen asthma and impair lung function.  Allergens in fragrances trigger headaches, migraines, asthma attacks and skin rashes.  The BfR therefore warns against certain fragrance compounds that cause contact eczema and are already banned in toys.  Insufficient ventilation can also cause carbon monoxide to accumulate, leading to dizziness, nausea or even poisoning.

Why do we hear so little about the dangers of scented candles?

Many of the effects described occur only with very frequent and prolonged use.  Studies show that overall exposure in most households remains below legal limits.  However we often ventilate less in winter, so pollutants accumulate.  Manufacturers are also not obliged to disclose all ingredients: in the USA less than ten percent of the fragrances used are known.  It is therefore hard for consumers to know which chemicals a candle contains.

Alternatives to scented candles and tips

• Use natural waxes: Candles made from beeswax, rapeseed or soy wax are more sustainable and emit fewer pollutants.  Scientists recommend these materials over paraffin products.  When shopping look for the RAL quality mark, which sets strict criteria for wicks, wax and colours.

• Choose unscented candles: Candles without added fragrance emit fewer VOC.  Citrus candles are particularly problematic because the limonene they contain reacts with air to form formaldehyde.

• Enjoy scent differently: Instead of candles you can use essential oils in cold nebulisers (diffusers).  They don’t heat the oils and don’t produce soot.  Nevertheless you should ventilate well because even natural fragrances can cause irritation.

• Burn candles correctly: Don’t let candles burn longer than necessary and avoid drafts.  Ventilate thoroughly before and after burning, ideally by airing cross‑wise for a few minutes.  Extinguish candles outdoors rather than blowing them out indoors to reduce smoke.

Monitor indoor air: Air‑quality monitors can measure CO₂, VOC and fine‑dust levels.  Such devices indicate when it’s time to ventilate.