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.
The industry / Review of other studies
The candle recipes tested in this study, the criteria for making them, and the study's funding all came from an advisory committee of candle and fragrance industry groups: the European Candle Association, National Candle Association, Latin American Candle Manufacturers Association, and the fragrance houses Arylessence, Belmay, Firmenich, Givaudan, International Flavors & Fragrances, Symrise, and Takasago.
Strong evidence.
Caveats
The authors' Declaration of Competing Interest states no known competing financial interests, alongside this acknowledged industry funding, study design input, and co-author industry affiliations (Arylessence, European Candle Association).
Source: Salthammer 2021, Environment International Industry-funded Link to this fact
The industry / Industry source
The fragrance industry's aggregate consumer exposure model did not include any estimate of inhaled fragrance exposure until 2017, when it added an inhalation route for air fresheners, scented candles, and personal-care sprays only — 23 years after the industry's 1994 safety package dismissed inhalation testing.
Moderate evidence.
Caveats
This is a modeled inhalation exposure fraction from a compartmental model run at single default parameter values, not measured breathing-zone data; the model's own validation against real chemical concentrations is reported in a companion paper (Safford et al. 2017) not yet in this evidence base.
Source: Comiskey 2017 (RIFM/Creme Global), Regulatory Toxicology and Pharmacology Industry-funded Link to this fact
The industry / Industry source
Some of the amount-per-use values feeding this industry exposure model come from very small studies — 10 Dutch adults for bar-soap-in-the-shower amounts, and a single non-distributional value for scented-candle amount per day — rather than large, representative samples.
Moderate evidence.
Caveats
Small external studies feeding a large aggregate model is a data-provenance observation, not itself evidence the resulting exposure estimates are biased in a particular direction; the paper does not report sensitivity analysis on these specific inputs.
Source: Comiskey 2017 (RIFM/Creme Global), Regulatory Toxicology and Pharmacology Industry-funded Link to this fact
The industry / Other evidence
In this industry model, the highest simulated exposure to vanillin came from body lotion (prestige range, P95 8.79 mg/kg bw/day), eau de parfum (8.34) and eau de toilette (6.34), while plug-in air freshener and scented candles — despite having the highest simulated in-product concentrations of vanillin — produced comparatively low exposure (P95 1.81 and 0.81 mg/kg bw/day) because there is no direct skin contact and the modeled inhalation fraction is low.
Moderate evidence: Modeled, not measured; industry-funded (RIFM); pattern shown for vanillin, generalized by the authors to the other 7 ingredients tested.
Source: Safford 2017, Regulatory Toxicology and Pharmacology Industry-funded Link to this fact
The industry / Measured in people or real products
The fragrance industry's own study found that grasping a scented candle for a total of 100 seconds transfers only about a quarter of a microgram per square centimeter of cinnamic aldehyde and eugenol to skin, which the authors say leaves a 1,000-fold or larger safety margin below the industry's own dermal sensitization threshold.
Moderate evidence.
Caveats
Industry-funded (RIFM and fragrance-industry co-authors); the comparison threshold ('NOEL-HRIPT') itself comes from an unpublished 2006 RIFM/IFRA technical dossier, not independently reviewed data. The paper itself states two different safety-factor numbers for cinnamic aldehyde in the same paper (~1,000 in its own table vs ~2,000 in its discussion text), an unresolved internal inconsistency.
Source: Api 2007 (RIFM), Regulatory Toxicology and Pharmacology Industry-funded Link to this fact
The industry / Measured in people or real products
In the same candle, d-limonene transferred to hands in undetectable amounts in every subject and every round tested, while cinnamic aldehyde and eugenol transferred consistently — the study authors could not explain the difference and did not test whether the missing d-limonene had oxidized inside the candle into breakdown products that are known allergens.
Moderate evidence.
Caveats
Industry-authored (RIFM); the authors themselves raise, but did not test, in-candle auto-oxidation of d-limonene as one possible explanation, citing separate evidence that limonene's oxidation products are allergenic.
Source: Api 2007 (RIFM), Regulatory Toxicology and Pharmacology Industry-funded Link to this fact
The industry / Review of other studies
The 2016 published critique that prompted Kim et al. to revise their scented-candle formaldehyde paper was authored by two National Candle Association staff members, not independent scientists.
Moderate evidence.
Caveats
The critique also identified a real methodological point (chamber concentrations do not equal room concentrations), which the responding authors accepted; industry authorship does not by itself make that specific point wrong.
Source: Kim et al. 2016, Journal of Hazardous Materials Link to this fact
The industry / Review of other studies
After a separate 'exception letter' sent in March 2015 by the National Candle Association, the original study's authors deleted a sentence reporting that formaldehyde in three scented-candle types (925, 1022, and 2098 ppb) exceeded workplace TLV (325 ppb) and PEL (730 ppb) limits, and softened a paper highlight from 'exposure levels of some species are high enough to exceed guideline values' to 'can approach or exceed certain guideline values.'
Moderate evidence.
Caveats
This is a documented instance of a trade association prompting language softening and deletion of a specific hazard finding in an academic paper's corrigendum; it does not mean the underlying revised emission-factor numbers (which went up, not down) are wrong.
Source: Kim et al. 2016, Journal of Hazardous Materials Link to this fact
The industry / Animal study
Scented candles are marketed and used in hotels, restaurants, and spas for a calming, stress-relieving aromatherapy effect, but in a mouse model, scented candle fume exposure did not significantly reduce the stress hormone corticosterone that chronic social-disruption stress had raised.
Moderate evidence.
Caveats
The study exposed mice to candle combustion fumes, not a controlled scent-only stimulus, so it cannot separate a candle's psychological/olfactory calming effect (untested here) from its combustion-product toxicity; a human user's subjective calming experience is not ruled out by this animal biomarker result.
Source: Chandrasekaran 2021, Current Research in Toxicology Link to this fact
The industry / Review of other studies
According to an industry report cited in this review, about 75% of scented candles are fragranced with artificial scents because they cost less than natural fragrance materials.
Weak evidence: Cited without an independently checkable primary source in this review; industry-report figure (ref. 48).
Source: Adamowicz 2019, Cancer Prevention Research Link to this fact
The industry / Other evidence
The US market for scented candles is estimated to be worth approximately $2 billion annually.
Weak evidence: Abstract-only/background figure; sourced from an industry-characterization paper (Ahn et al. 2015) not independently verified in this evidence base.
Source: Nazir et al. 2024, Annals of Medicine & Surgery Link to this fact
The industry / Other evidence
A study by Petry et al. (2014) concluded that, under normal conditions of use, scented candles do not pose known health risks to consumers.
Weak evidence.
Caveats
Petry et al. 2014 is not yet a evidence base primary; its funding/COI has not been independently verified here, though several co-authors and the paper's risk-assessment framing are consistent with fragrance-industry-connected toxicology work. It is one study among several in this same Viewpoint reaching the opposite conclusion (Adamowicz 2019, Derudi 2014, Chandrasekaran 2021).
Source: Singh 2023, Environmental Science & Technology Link to this fact
Information, not medical advice. See also: myths we won’t tell you.