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.
Laws and loopholes / Review of other studies
History shows removing the exposure works: as industrial turpentine use fell from 94.5% of US supply as a solvent in 1935 to 4.5% in 1975, turpentine skin allergy declined with it.
Moderate evidence: Ecological historical correlation.
Source: Karlberg & Lepoittevin 2021, Contact Dermatitis Link to this fact
Laws and loopholes / Review of other studies
Official limits for the same gas odorant differed about 280-fold in 2009: Germany allowed 50 ppm at work, a Dutch health agency derived 0.18 ppm, and the US had no limit.
Moderate evidence: Regulatory values as reported by the paper (2009); may have been revised since.
Source: Baur & Bittner 2009, American Journal of Industrial Medicine Link to this fact
Laws and loopholes / Measured in people or real products
Workers with fragrance-related asthma were twice as likely as other work-asthma cases to still be exposed at work (50% vs 26%) and more often had workers' compensation claims denied (30% vs 21%), though ER visit and hospitalization rates were the same.
Moderate evidence: Interviewed cases only (~58% of fragrance cases); unadjusted.
Laws and loopholes / Review of other studies
A fragrance-and-flavor company reported that about half of the chemicals it handles are classified hazardous, and that few of the more than 3,000 flavoring substances in use have workplace exposure limits.
Moderate evidence: Industry self-description, no inventory published; flavor materials at one company.
Source: Angelini 2016, PLoS ONE Industry-funded Link to this fact
Laws and loopholes / Review of other studies
A 2015 CMAJ editorial (Flegel & Martin, CMAJ 187:1187, DOI 10.1503/cmaj.151097) states hospital environments free from artificial scents 'should become a uniform policy, promoting the safety of patients, staff and visitors alike'; the US CDC's own workplace policy separately says fragrance 'is not appropriate for a professional work environment' (CDC wording still unverified against a primary CDC source).
Moderate evidence.
Caveats
CMAJ quote now verified against the primary editorial, now in our evidence base (src-2015-artificial-scents-no-place-hospitals): exact wording is 'should become a uniform policy' (ASEQ-EHAQ's paraphrase drops the article 'a', not a substantive misquote). The editorial is opinion/commentary, not a study — its own cited prevalence numbers (30% scent sensitivity, 27% of asthmatics worsened) are the same Caress & Steinemann survey figures used elsewhere in our evidence base. CDC portion remains unverified; the CMAJ editorial itself never mentions the CDC.
Source: ASEQ-EHAQ 2020 (quoting CMAJ 2015 and CDC) Link to this fact
Laws and loopholes / Self-reported survey
MCS is legally recognized as a disability in Canada, but in a national survey most people with MCS who asked for a workplace or housing accommodation before the pandemic (85% of 119) were refused at least once (the paper's own figure: 'at least 78%').
Moderate evidence.
Caveats
Self-reported, cross-sectional, community-based convenience sample of 119 recruited substantially through an MCS advocacy charity's own channels (ASEQ-EHAQ, which also funded the study and paid some authors); over-represents Quebec; likely under-represents the most severely affected.
Source: Diallo 2026 Link to this fact
Information, not medical advice. See also: myths we won’t tell you.