Every fact on this site, with its evidence grade, its caveats, and a link to the source.
We start you on the strong ones: findings that have been replicated or come from one large, well-controlled study. Moderate and weak facts are here too, labeled for what they are. Use “Link to this fact” to share a single card.
Green, natural and unscented / Measured in people or real products
The unscented 'plain' paraffin candle used as this study's own combustion reference produced the third-highest formaldehyde level of the six candles tested when lit (925 ppb), higher than two of the five scented candles.
Moderate evidence.
Caveats
Single lab, six products, no replication; wax type (paraffin vs. palm) did not track cleanly with formaldehyde output either, so this alone doesn't identify which factor (wax, wick, dye, or fragrance) actually controls it.
Source: Ahn et al. 2015, Journal of Hazardous Materials Link to this fact
Green, natural and unscented / Other evidence
Candles made from renewable waxes (beeswax, soy, coconut, palm) scented with natural essential oils are generally safer and more sustainable than paraffin candles, but still carry an environmental cost through deforestation and habitat destruction from increased crop demand.
Weak evidence.
Caveats
No emissions or land-use quantification given; our own chamber data (Salthammer 2021, Andersen 2021) also show wax type has little effect on formaldehyde/PAH output compared to fragrance load, so a wax switch alone may not reduce indoor-air health risk even if it changes the environmental footprint.
Source: Singh 2023, Environmental Science & Technology Link to this fact
Information, not medical advice. See also: myths we won’t tell you.