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.
Health effects / Animal study
Some older fragrance ingredients were neurotoxic: the nitromusk musk ambrette caused nerve damage in animal studies and was later withdrawn.
Strong evidence.
Caveats
Primary now read directly: Spencer 1984 is a large (N=220), dose-ranging, dual-route (dietary+dermal), histopathologically confirmed (light+EM) study showing clear dose-response demyelination and distal axonal degeneration. Note: musk ambrette's actual withdrawal from skin-contact products was driven primarily by a separate photoallergy finding (Cronin 1984), not directly by this neurotoxicity data, which RIFM had already argued had an adequate safety margin (>600) via absorption data (Ford 1994). Doses producing consistent neurotoxic effects are 50-250x the industry's own estimated maximum human exposure.
Source: Curtis 2004 (citing Spencer 1984), Environmental Health Perspectives Link to this fact
Health effects / Review of other studies
Chamber studies of asthma exclude moderate and severe asthmatics by design, and the one study that directly compared severity bands found the excluded group had the largest airway response — so these studies likely underestimate how sensitive people with asthma really are.
Strong evidence.
Caveats
Confirmed by a separate 103-study systematic review (Johansson 2016), whose own quality criteria excluded moderate/severe asthma in every included study; its one direct severity comparison (Linn et al. 1987, sulfur dioxide) found the moderate/severe group had the largest SRaw/FEV1 impairment, though not statistically significant in that small sample. Direction is now doubly confirmed (two independent reviews built on the same design flaw); magnitude of the underestimate is still not quantified.
Source: Kleinbeck & Wolkoff 2024, Archives of Toxicology Industry-funded Link to this fact
Health effects / Review of other studies
Chamber studies show irritant gases cause severe airway narrowing in people with asthma at concentrations at or below standard workplace exposure limits: asthmatics had severe bronchoconstriction to sulfur dioxide at about 0.4 ppm (1.1 mg/m3) after just 5-10 minutes of exercise, and to sulfuric acid at about 1 mg/m3.
Strong evidence.
Caveats
Quantified by Johansson 2016 (103-study systematic review): asthmatics showed severe airway narrowing (SRaw >=200%, FEV1 drop >=20%) to sulfur dioxide at >=1.1 mg/m3 (~0.4 ppm) after 5-10 min exercise and moderate-severe responses to sulfuric acid around 1 mg/m3 (oronasal) or 0.35 mg/m3 (mouth-only); both sit at or below typical occupational exposure limits for these substances (e.g. ACGIH SO2 TWA ~2 ppm/STEL 5 ppm; background knowledge, verify against current ACGIH tables). This is now primary chamber data, not only a secondary citation of Baur 2012's occupational-asthma review. Still not specific to fragrance chemicals; these are combustion/industrial irritant gases. Strong for sulfur dioxide and sulfuric acid only; no equivalent chamber data exist for fragrance chemicals, so do not transfer the grade to fragrance.
Source: Kleinbeck & Wolkoff 2024, Archives of Toxicology Industry-funded Link to this fact
Health effects / Review of other studies
In the same EPA review, diethyl phthalate (DEP), the phthalate used in fragrance, had only 'slight' evidence of male reproductive effects, the weakest of six phthalates, even though people are exposed to it the most.
Strong evidence: Use to set the record straight, not to accuse fragrance; 'slight' is not 'none' (more high-confidence studies needed).
Source: Radke 2018 (US EPA), Environment International Link to this fact
Health effects / Measured in people or real products
In the largest controlled test of its kind, 130 healthy young women breathing an indoor chemical mixture with and without ozone for 140 minutes showed no significant change in symptoms, lung function, attention or the stress hormone cortisol.
Strong evidence: Healthy women only; asthma and chemical sensitivity excluded; one 140-min exposure at 1.8 air changes/h; eye-blink rate not measured.
Source: Fiedler 2005, Environmental Health Perspectives Link to this fact
Health effects / Measured in people or real products
A systematic review of 103 controlled chamber studies found asthmatics develop severe airway narrowing to sulfur dioxide at concentrations around 1 mg/m3 (about 0.2-0.4 ppm) after just 5-10 minutes of exercise, while healthy people showed no response even at 15 mg/m3; individual dose-response modeling put asthmatics about 9 times more sensitive to sulfur dioxide than healthy people.
Strong evidence: Sulfur dioxide is a combustion/industrial gas, not a fragrance chemical; asthmatic subjects were mild cases only (severe asthma excluded by design).
Source: Johansson 2016, Critical Reviews in Toxicology Link to this fact
Health effects / Measured in people or real products
Every controlled chamber study in a 103-study review of asthma and airborne chemicals excluded people with moderate or severe asthma by design; the one study that directly compared severity groups found the more severe group had the largest airway response, though not statistically significant in that small sample.
Strong evidence: Direction, not magnitude: the comparison (Linn et al. 1987) was underpowered and did not reach significance.
Source: Johansson 2016, Critical Reviews in Toxicology Link to this fact
Health effects / Animal study
Musk ambrette, once a widely used musk fixative in fragrances (over 100,000 lb/year in the US since the 1920s), caused nerve-fiber demyelination and degeneration in a large industry-funded rat study of 220 animals, with hindlimb weakness ranging from isolated cases at moderate doses to complete weakness at the highest dose tested.
Strong evidence.
Caveats
Large (N=220), dose-ranging, dual-route (dietary+dermal) primary with clear dose-response and light+EM histopathology confirmation; doses producing consistent effects are 50-250x the industry's own estimated maximum human exposure.
Source: Spencer 1984, Toxicology and Applied Pharmacology Industry-funded Link to this fact
Health effects / Review of other studies
The cosmetics industry's own expert safety panel states plainly, in its own report, that no data exist — published or industry-submitted — on whether PTFE (Teflon) is absorbed through the skin or how the body distributes, metabolizes or excretes it.
Strong evidence.
Caveats
Absence of data is not evidence of harm; the tested endpoints (acute toxicity, irritation, sensitization, genotoxicity) were negative at cosmetic use concentrations. This narrow claim is about dermal absorption/ADME only — it does not extend to endocrine or environmental effects, which this document does not address at all.
Source: CIR 2018 Industry-funded Link to this fact
Health effects / Measured in people or real products
Most patients with scent- and chemical-triggered breathing symptoms in this study (8 of 12) were already taking asthma inhalers or steroid inhalers and said the drugs gave little or no relief, matching an independent Canadian clinic's finding that a similar scent-triggered condition does not respond to asthma medication.
Strong evidence.
Caveats
Both this and the corroborating study (Hoy 2010) are single-clinic case series (n=12 and n=30); 'little relief' is patient-reported, not measured by a controlled inhaler-response trial.
Information, not medical advice. See also: myths we won’t tell you.