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.
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
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 / 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.
Health effects / Other evidence
The EU's safety margin of 192 for conditioner quats (cetrimonium, steartrimonium, behentrimonium chloride) rests on a skin-absorption value borrowed from a different, shorter-chain chemical (laurtrimonium bromide, rat, 1979) and a 12-month rat study of cetrimonium bromide; the committee itself called the absorption value a compromise.
Strong evidence: The committee also says rat skin is usually more permeable than human skin, so 3.15% may overestimate; the MoS is a worst-case figure against a benchmark of 100.
Source: SCCS 2009 trimoniums, SCCS opinion (PDF) Link to this fact
Information, not medical advice. See also: myths we won’t tell you.