Don’t take our word for it. Here’s every fact on this site, with its evidence grade, its caveats, and a link to the source, so you can check us.
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 / Other evidence
RIFM's founding scientific director personally authored the sole primary study behind the fragrance industry's 'quenching' safety exception; IFRA later codified it into a formal use-with-limonene rule (≥25% d-limonene) that required a higher proportion of the 'quenching' terpene than Opdyke's own 1976 test (~20% d-limonene) actually used.
Moderate evidence: The evidence base does not have IFRA's own documentation of why 25% (rather than the tested ~20%) was chosen, or of when/why the quenching exception was later withdrawn.
Source: Ford 1994 (RIFM), citing Opdyke 1976 Industry-funded Link to this fact
The industry / Measured in people or real products
Despite thousands of positive allergy-test reactions to oxidized limonene and linalool reported worldwide, the fragrance industry's own market-testing program concluded that where people are actually getting exposed to these allergens "remains elusive" — the industry itself has not identified the real-world consumer-product source of a widely documented skin allergy.
Moderate evidence.
Caveats
This is the industry's own conclusion, from an industry-funded study; it does not mean the allergy is not real or not caused by fragrance chemicals — only that the specific consumer-product exposure route has not been chemically confirmed even by the party with the strongest incentive to find an innocuous explanation.
Source: Natsch 2019, Food and Chemical Toxicology 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 / Measured in people or real products
All cleaning products tested in this study (laundry detergent, fabric softener, dust/floor/glass cleaners, and a smoke remover) contained detectable VOCs; alkanes (mainly n-tetradecane, 87 µg/mL in the laundry detergent) and terpenes (mainly limonene, up to 64 µg/mL in the smoke-remover spray) were the dominant classes, while chlorine bleach (not itself tested for VOCs but used liberally) was linked to the chloroform and carbon tetrachloride found in laundry-room air.
Moderate evidence: Only 7 products from one hotel were tested; formulations vary by brand and hotel.
Information, not medical advice. See also: myths we won’t tell you.