Do candles release formaldehyde indoors?
Yes. Scented candle combustion produces formaldehyde plus a mix of other VOCs that irritate airways and damage lung tissue.
What's actually in it
Candle flames are small combustion reactors. Paraffin wax feeds the flame; fragrance oil evaporates through it. The flame breaks both down into formaldehyde, benzene, acetaldehyde, and toluene. Even "clean" candles made of soy or beeswax with added fragrance release these because the fragrance itself is the main source.
Formaldehyde is a known carcinogen. It doesn't just affect factory workers. In a small closed room with a candle running for hours, the air load can approach workplace exposure limits.
What the research says
A 2025 study in Front Public Health collected VOCs from burning scented candles and tested them on rats. The animals showed oxidative stress, airway inflammation, and lung injury. Computer modeling confirmed that formaldehyde and several other VOCs crossed the lung barrier into blood.
Reduce exposure by skipping candles with synthetic fragrance, running them in well-ventilated rooms only, and never in bedrooms where a baby or child sleeps. Unscented beeswax candles produce far fewer VOCs than scented paraffin.
The research at a glance
| Study | Journal | Year |
|---|---|---|
| Toxicological evaluation of volatile organic compounds emitted from scented candles. | Front Public Health | 2025 |
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