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 / 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 / Self-reported survey
About 1 in 7 Danish adults (14%) reported fragrance-triggered symptoms at least weekly, and 5% had changed where they shop, how they travel, or how they work because of them.
Moderate evidence: Self-report.
Source: Elberling 2005, Clinical and Experimental Allergy Link to this fact
Health effects / Review of other studies
Cleaning products were the suspected exposure in 236 of 1,915 (12%) confirmed work-related asthma cases across California, Massachusetts, Michigan, and New Jersey (1993-1997); in California, janitors and cleaners had roughly double the confirmed-case rate of all other occupations combined (4.3 vs 2.3 per 100,000 workers).
Moderate evidence.
Caveats
Now traced to its primary source (Rosenman 2003), not a secondary citation. But the underlying surveillance system's own authors say it misses 53-87% of true cases (Michigan capture-recapture) and that up to 37% of confirmed cases in such systems may not be truly work-related (Malo et al., cited by Rosenman); 'cleaning products' is a broad, mostly unspecified chemical category (36% of named agents never identified further than 'cleaning compound'), not fragrance-specific (limonene only 2/300 exposure counts).
Source: Nazaroff & Weschler 2004, Atmospheric Environment Link to this fact
Health effects / Measured in people or real products
In a Toronto clinic for work-related breathing problems, about 1 in 10 referred workers had an irritable larynx (throat) syndrome rather than asthma; perfumes and cleaning agents, bleaches and air fresheners were among the named triggers.
Moderate evidence.
Caveats
Single referral clinic, retrospective, n=30; perfume named by 5/30 and cleaning agents/fresheners by 4/30; 10% of referrals, not of workers. Morrison 1999, the founding case series behind the diagnostic criteria Hoy applied, independently found perfume was a named trigger in only 26% (10/39) of its own ILS cohort, behind reflux (72%) and other airborne irritants (51%) — the syndrome is not fragrance-specific at its point of origin either.
Health effects / Measured in people or real products
About 80% of workers with scent- and irritant-triggered irritable larynx syndrome were women, versus 24–52% of workers with occupational asthma at the same clinic.
Moderate evidence: N=30, one clinic; referral and care-seeking may differ by sex.
Health effects / Measured in people or real products
Over 20 years (1993–2012), California's work-related asthma surveillance confirmed 270 cases linked to perfume or air fresheners at work, 3.8% of all confirmed cases; perfume was the 9th most common workplace asthma exposure.
Moderate evidence: Surveillance count of physician-diagnosed, reported cases; misses >=2/3 of cases; no objective testing required; excludes fragranced cleaners.
Health effects / Measured in people or real products
94% of workers with fragrance-related work asthma in California were women, mostly in offices, health care, and schools, and most cases came from perfume worn by others.
Moderate evidence: Authors attribute the sex skew to occupation and exposure, not susceptibility; care-seeking bias possible.
Health effects / Self-reported survey
Of all personal care product types, perfumes and colognes had the highest hazard ratings in the Environmental Working Group's Skin Deep database, and adults aged 18–39 used the highest-rated ones (average 7.2 of 10, vs 5.9 for those 60 and over).
Moderate evidence: EWG hazard ratings from listed ingredients, not measured toxicity or exposure; 39% of perfumes used could not be rated.
Source: Barrett 2025, Journal of Exposure Science & Environmental Epidemiology Link to this fact
Health effects / Review of other studies
A systematic review of workplace irritants found that people with pre-existing airway sensitivity (atopy plus non-specific bronchial hyper-responsiveness) can develop new-onset asthma from chronic, repeated exposure to an irritant at concentrations below the official occupational exposure limit.
Moderate evidence.
Caveats
General occupational-irritant literature (solvents, isocyanates, dusts, gases), not fragrance-specific; the below-OEL pattern is narrative synthesis over 3 older sources plus compiled case-series examples, not an independently SIGN 2+-graded finding.
Source: Baur, Bakehe & Vellguth 2012, Journal of Occupational Medicine and Toxicology Link to this fact
Health effects / Measured in people or real products
Cleaning products were the suspected exposure in 236 of 1,915 (12%) confirmed work-related asthma cases across California, Massachusetts, Michigan, and New Jersey, 1993-1997; most were new-onset asthma (80%) and about a fifth were consistent with reactive airways dysfunction syndrome, an irritant-induced, non-allergic asthma type.
Moderate evidence.
Caveats
This is a primary surveillance source, not a population prevalence estimate: the authors' own capture-recapture analysis found the surveillance system misses 53-87% of true work-related asthma cases in Michigan, and up to 37% of confirmed cases in such systems may not be truly work-related (Malo et al., cited by the authors). Fragrance/limonene was a minor named agent (2 of 300 exposure counts); bleach, acids, disinfectants, and quaternary ammonium compounds dominate.
Source: Rosenman 2003, Journal of Occupational and Environmental Medicine Link to this fact
Health effects / Measured in people or real products
In California, janitors and cleaners had roughly double the confirmed work-related asthma rate of all other occupations combined (4.3 vs 2.3 per 100,000 workers).
Moderate evidence.
Caveats
Single-state comparison using SENSOR case counts against 1990 census occupation denominators; not adjusted for other confounders; occupations with the highest overall work-related-asthma rates (firefighters, correctional officers) were not cleaning-related, so elevated rate alone does not isolate cleaning-product causation.
Source: Rosenman 2003, Journal of Occupational and Environmental Medicine Link to this fact
Health effects / Measured in people or real products
In a 2021 audit of 50 stores across 8 Boston neighborhoods, stores in lower-income Roxbury and Mission Hill were more than twice as likely to stock a hair product with a high (7-10) Environmental Working Group hazard score than stores in higher-income, predominantly White Beacon Hill (risk ratio 2.3 for both).
Moderate evidence.
Caveats
Retail-shelf audit of what stores stock, not what people buy or use; EWG hazard score is a derived ingredient-label rating, not a measured chemical concentration; only 2 of 6 neighborhood comparisons reached statistical significance, and Chinatown was excluded for 94% missing scores.
Source: Chan 2023, Environmental Health Perspectives Link to this fact
Health effects / Measured in people or real products
People with mild asthma performed a concentration task significantly less accurately than healthy people during a 3-hour ozone-limonene chamber exposure, despite working faster.
Moderate evidence: Single study, no unexposed control arm, so it is not established that the chemistry (rather than general chamber occupancy or task load) caused the accuracy difference.
Health effects / Review of other studies
Quaternary ammonium compounds such as benzalkonium chloride (BAC) and didecyldimethylammonium chloride (DDAC) have been linked to occupational asthma, contact dermatitis, and urticaria in healthcare workers, professional cleaners, and hairdressers with heavy, repeated exposure to disinfectants, antiseptics, and cosmetic preservatives.
Moderate evidence.
Caveats
Evidence is case reports, small cohorts, and a few specific-inhalation-challenge studies of occupational/disinfectant/cosmetic exposure, not laundry products; two cited cohort studies of QAC and healthcare-worker asthma directly disagree (see contradictions).
Source: Peyneau 2022, Frontiers in Toxicology Link to this fact
Health effects / Self-reported survey
Among 543 healthcare workers in 7 French hospitals/clinics, occupational exposure to quaternary ammonium compounds (QACs, e.g. benzalkonium chloride) was linked to about 7.5x higher odds of reported physician-diagnosed asthma (adjusted OR 7.56, 95% CI 1.84-31.05) and about 3.2x higher odds of nasal symptoms at work (adjusted OR 3.21, 95% CI 1.42-7.22), after adjustment for age, gender, smoking, BMI, and atopy.
Moderate evidence.
Caveats
Single cross-sectional cohort (not replicated by an independent group); the asthma outcome relies on self-report plus doctor confirmation, not spirometric testing; the confidence interval's lower bound (1.84) shows a wide range of plausible effect sizes; healthy-worker survivor bias could have caused an underestimate, especially among cleaners.
Source: Gonzalez 2014, Clinical & Experimental Allergy Link to this fact
Health effects / Measured in people or real products
Only 6.5% of tested healthcare workers (32 of 494) had detectable specific IgE antibodies to quaternary ammonium compounds, and this was not significantly associated with reported asthma, new-onset asthma, or nasal symptoms — despite QAC exposure itself being strongly associated with those same outcomes. The study authors read this pattern as pointing to an irritant, not an IgE-mediated allergic, mechanism.
Moderate evidence.
Caveats
Absence of an IgE signal does not rule out a non-IgE immunological mechanism; specific IgE was only tested against a general quaternary ammonium radical, not against every specific QAC compound (e.g. benzalkonium chloride vs. didecyldimethylammonium chloride) separately.
Source: Gonzalez 2014, Clinical & Experimental Allergy Link to this fact
Health effects / Self-reported survey
Reported physician-diagnosed asthma prevalence varied sharply by healthcare occupation: 16.1% among nurses, 16.7% among auxiliary nurses, 7.7% among cleaners, 5.1% among other healthcare workers, and 3.4% among administrative staff (overall 11.2%, p=0.003).
Moderate evidence.
Caveats
Descriptive prevalence from a single cross-sectional cohort; differences between nurses and cleaners may partly reflect a healthy-worker survivor effect (cleaners with severe asthma more likely to have left the job) rather than only differences in true exposure or risk.
Source: Gonzalez 2014, Clinical & Experimental Allergy Link to this fact
Health effects / Review of other studies
Benzalkonium chloride (BAK), the preservative in most glaucoma eye drops, accumulates in the trabecular meshwork and other deep ocular tissues after chronic topical use and has a tissue half-life of about 20 hours in the corneal/conjunctival epithelium.
Moderate evidence: Accumulation is well documented; a causal link between that accumulation and disease progression is not established by these detection studies alone.
Source: Rasmussen et al. 2014, Journal of Ocular Pharmacology and Therapeutics Industry-funded Link to this fact
Health effects / Other evidence
BAK-exposed trabecular meshwork tissue and cells share the same qualitative cellular and molecular damage signature — cell loss, apoptosis, increased reactive oxygen species, extracellular matrix accumulation, decreased outflow, fibronectin upregulation, and cellular senescence — seen in the trabecular meshwork of primary open-angle glaucoma patients.
Moderate evidence.
Caveats
This shared signature is correlational. The review states explicitly that the causal hypothesis (BAK worsens glaucoma, rather than merely resembling it) is unproven and was, at the time of writing, only beginning to be tested in a nonhuman-primate model. See C324.
Source: Rasmussen et al. 2014, Journal of Ocular Pharmacology and Therapeutics Industry-funded Link to this fact
Health effects / Self-reported survey
Weekly use of disinfectant/cleaning sprays at work was associated with worse asthma control in US nurses (OR 1.50, 95% CI 1.16-1.94 for poorly controlled; OR 1.38, 95% CI 1.00-1.92 for very poorly controlled), and the association held even among nurses who used sprays less than once a week.
Moderate evidence.
Caveats
Self-reported spray use; the paper attributes the effect to higher inhalation potential from spray application rather than to a specific chemical, since sprays covered multiple product types (surface, patient care, air-refreshing).
Source: Dumas 2017, European Respiratory Journal Link to this fact
Health effects / Review of other studies
The same authors' own worked example for ammonia — comparing a mouse near-zero-effect threshold (42 ppm) to the human no-effect level, then adding a further factor to account for ordinary variation between people — lands on a combined safety margin of about 4 to 5, not the smaller factor of about 2 that a later 2024 review attributes to this paper for protecting sensitive groups.
Moderate evidence.
Caveats
Single worked example for one chemical (ammonia); the 'about 2' figure the authors separately cite is explicitly for age/sex/lifestyle/disease combined in a general population, not derived fresh in this paper, and not tested against moderate or severe asthma/allergy.
Source: Nielsen & Wolkoff 2017, Regulatory Toxicology and Pharmacology Industry-funded Link to this fact
Health effects / Lab study (cells or chemistry)
BAK's ocular toxicity is proposed to work partly through mitochondria: because BAK is positively charged and mitochondria are the only negatively charged compartment inside cells, cell studies cited in this review found BAK triggers oxidative stress and can inhibit mitochondrial function by more than 90%.
Moderate evidence: Mechanism drawn from in vitro/cell-culture studies cited by the review, not measured directly in intact human eyes.
Source: Goldstein 2022, Eye Industry-funded Link to this fact
Health effects / Lab study (cells or chemistry)
Exposing primary human bronchial epithelial cells (air-liquid interface culture) to a disinfectant-concentration (0.4%) benzalkonium chloride aerosol for 24 h produced 2,810 differentially expressed genes (1,475 up, 1,335 down), mapping onto DisGeNET disease networks for asthma, COPD, and pulmonary fibrosis; IL1RL1 and IL6R (upregulated) are independently reported as elevated in human asthma patients.
Moderate evidence.
Caveats
Single cell-culture model, one lab, no animal or human validation of the transcriptomic findings; the authors themselves call the existing evidence that BKC causes respiratory disease in humans 'insufficient' and frame this as hypothesis-generating.
Source: Kim et al. 2025, Ecotoxicology and Environmental Safety Link to this fact
Health effects / Government agency
An international expert working group convened by the World Health Organization and UN Environment Program concluded that close to 800 chemicals are known or suspected to interfere with hormone receptors, hormone synthesis, or hormone conversion, but only a small fraction of them have been tested for whether they actually cause overt endocrine effects in an intact organism.
Moderate evidence.
Caveats
This is a 2012 expert-consensus count covering every kind of suspected endocrine disruptor (industrial chemicals, pesticides, plastics, cosmetic ingredients, natural compounds), not a fragrance-specific count, and the report is now well over a decade old.
Source: WHO/UNEP 2012 Link to this fact
Health effects / Government agency
Benzophenone's oxidative metabolite 4-hydroxybenzophenone, which is estrogenic in vitro (MCF-7 cells, ERalpha binding) and in vivo (rat uterotrophic assay), can also be formed by ultraviolet or sunlight irradiation of benzophenone itself, not only by enzymatic metabolism; the Working Group noted this matters because benzophenone has been used as a UV filter in cosmetics.
Moderate evidence.
Caveats
Photochemical formation and estrogenic activity of the photoproduct are drawn from cited primary studies (Hayashi et al. 2006, Nakagawa & Tayama 2001/2002) summarized in the monograph, not independently re-verified here; this describes the parent compound's own photoproduct, not a sunscreen-derivative UV filter's photoproduct.
Source: IARC 2013 Link to this fact
Health effects / Measured in people or real products
Two German gas-works plumbers who repeatedly hand-poured the gas odorant tetrahydrothiophene in an unventilated room developed chronic rhinitis and lasting airway obstruction; neither had allergies on skin testing, and the accident insurer accepted both as occupational disease.
Weak evidence: Two case reports; exposure estimated, not measured; one worker smoked ~16 pack-years; industrial odorant, not fragrance.
Source: Baur & Bittner 2009, American Journal of Industrial Medicine Link to this fact
Health effects / Review of other studies
A cohort of laborers acutely exposed to gasoline vapors above allowed limits during an underground tunnel-excavation job later developed symptoms similar to those reported in multiple chemical sensitivity, and the study authors argued the workers' sociocultural profile made simple psychosomatic suggestibility an unlikely sole explanation.
Weak evidence.
Caveats
Cited secondhand from Davidoff et al. (primary study not yet in our evidence base); occupational cohort with no independent control for pre-existing chemical sensitivity, and "unlikely to be suggestible" is the original authors' qualitative judgment, not a tested exclusion of a psychological contribution.
Source: Rossi 2018, Journal of Occupational & Environmental Medicine Link to this fact
Health effects / Other evidence
In cultured human trabecular meshwork cells, BAK concentrations as low as 0.00002% — well below the 0.005-0.02% range found in commercial glaucoma drops — significantly reduced cell density and cell growth.
Weak evidence.
Caveats
Single in vitro study; bovine trabecular meshwork cells in a different study required about 50x that concentration (0.001%) to show the same effect, so results vary by species and cell state.
Source: Rasmussen et al. 2014, citing Samples et al. 1989, Journal of Ocular Pharmacology and Therapeutics Industry-funded Link to this fact
Health effects / Lab study (cells or chemistry)
BKC aerosol exposure altered secretion of 166 proteins in bronchial epithelial cells (84 up, 82 down); a gene-disease network of the upregulated secreted proteins linked GDF15, MMP1, and VEGFA (each increased two- to three-fold) to atherosclerosis and cardiovascular disease, suggesting inhaled BKC could have a direct, not just stress-mediated, systemic cardiovascular effect.
Weak evidence.
Caveats
This is a novel hypothesis from one cell-culture secretome analysis cross-referenced against disease-association databases (DisGeNET, CTD), not a measured blood biomarker change in an exposed animal or human; the authors describe it as warranting further investigation.
Source: Kim et al. 2025, Ecotoxicology and Environmental Safety Link to this fact
Health effects / Other evidence
A screening-level model of a heavy occupational scented-candle exposure (aromatherapy workers, 8 hours a day for 40 years) found a 95th-percentile lifetime lung cancer risk from PAHs alone of 1.20 in a million, marginally exceeding the commonly used 1-in-a-million risk threshold, under the single worst combination of low ventilation and intermediate humidity tested.
Weak evidence.
Caveats
PAH-only estimate (excludes co-emitted benzene, formaldehyde, and particulate matter that would add to total risk); occupational 8h/day/40-year exposure scenario, not typical home candle use; single candle formulation and small chamber; only the 95th-percentile Monte Carlo estimate under the single worst condition exceeded the threshold, not the mean case.
Information, not medical advice. See also: myths we won’t tell you.