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.
Hidden ingredients / Review of other studies
Fragrance turns up in products people don't think of as scented: household cleaners and detergents, tampons and panty liners, medicines, medical devices, toys, and candles.
Moderate evidence: Qualitative list of exposure sources.
Source: Sukakul 2024, Acta Dermato-Venereologica Industry-funded Link to this fact
Hidden ingredients / Review of other studies
Unlike most retail candles labeled only "fragrance," the candles in this study had their full wax and fragrance formulations precisely known and reported, because they were purpose-built for the research with fragrance industry cooperation.
Moderate evidence.
Caveats
This transparency applies only to these custom research candles, not to any candle sold at retail; the study does not show that any specific commercial candle's contents are disclosed.
Source: Salthammer 2021, Environment International Industry-funded Link to this fact
Hidden ingredients / Measured in people or real products
Before candles were lit, the largest class of chemicals detected across the products was esters (30 of 34 dominant compounds identified), which manufacturers disclose on the label only as 'fragrance' or 'aroma oil.'
Moderate evidence.
Caveats
Most of these ester identities were quantified by a predictive (ECN) method rather than authentic calibration standards, so individual concentrations carry more uncertainty than the 24 directly-calibrated target compounds; no specific health hazard was established here for most of the named esters.
Source: Ahn et al. 2015, Journal of Hazardous Materials Link to this fact
Hidden ingredients / Animal study
GC-MS of the scented candle's emissions detected methylene chloride (2.71% of peak area, a carcinogen with two known toxic-metabolite pathways) and the phthalate DEHP (0.1%), neither of which would appear on a candle's fragrance or wax label.
Moderate evidence.
Caveats
Detected in headspace/combustion emissions, not necessarily added as ingredients; percentages are of total VOC peak area, not of candle mass, and the specific candle's ingredient list is not published.
Source: Mohamed et al. 2025, Frontiers in Public Health Link to this fact
Information, not medical advice. See also: myths we won’t tell you.