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.
Green, natural and unscented / Government agency
On the page describing its Product Endorsement Scheme, Allergy UK publishes no fragrance-specific criteria: the word "fragrance" does not appear anywhere on the page, and the only stated assurance is that a product has been "scientifically tested by Allergy UK to confirm its claims," with no ingredient list, protocol, or threshold given.
Moderate evidence: Absence of published criteria on this page is not proof the underlying testing process lacks criteria internally; it is only what the public page discloses.
Source: Allergy UK 2026 Link to this fact
Green, natural and unscented / Government agency
EPA's Safer Choice fragrance-free certification is a documentary ingredient-list review, not a finished-product lab test: EPA checks that a product already meets the full Safer Choice Standard, then checks its ingredient list against the industry's own IFRA Transparency List of fragrance materials.
Moderate evidence.
Caveats
No chemical analysis of the finished product is described; verification rests on declared ingredient lists checked against two lists (SCIL and the IFRA Transparency List), not analytical chemistry or clinical testing.
Source: US EPA Safer Choice Link to this fact
Green, natural and unscented / Government agency
A product carrying the EPA Safer Choice 'fragrance-free' label can still have a smell, because ordinary functional ingredients such as surfactants and solvents can carry an odor without being classified as a fragrance material.
Moderate evidence: EPA states this directly; it is a definitional carve-out, not a measurement of any certified product's actual odor.
Source: US EPA Safer Choice Link to this fact
Green, natural and unscented / Government agency
Health Canada's cosmetic labeling guidance on 'unscented'/'fragrance-free' does not cover laundry detergent, fabric softener, or dryer sheets; Canada's legal definition of 'cosmetic' (Food and Drugs Act s.2) covers products for the complexion, skin, hair, or teeth, not fabric.
Moderate evidence.
Caveats
The 'cosmetic' definition and its exclusion of fabric-care products is confirmed directly from the source text; that laundry products instead fall under Canada's consumer chemical product safety rules (CCPSA) is background knowledge, not itself stated in either captured Health Canada page, so graded moderate rather than strong.
Source: Health Canada 2026 Link to this fact
Green, natural and unscented / Measured in people or real products
Laundry products labeled 'free and gentle' genuinely excluded fragrance (0% contained it across every product category), but still commonly contained preservative allergens (MI in 57.1% of free-and-gentle detergents) and surfactant allergens (decyl/lauryl glucoside in 28.6-33.3% of free-and-gentle detergents and stain removers).
Moderate evidence: N=7-13 per free-and-gentle subgroup depending on category; label survey only.
Green, natural and unscented / Measured in people or real products
In the same test house and wax warmer, an unscented wax melt produced no significant terpene release and no measurable nanoparticle formation, showing that the fragrance chemicals — not the melted wax itself — are what drives the particle-forming reaction.
Moderate evidence: A single unscented product tested as one control condition; supports the mechanism but is not itself a survey of unscented products generally.
Source: Patra et al. 2025, Environmental Science & Technology Letters Link to this fact
Green, natural and unscented / Review of other studies
Most 'natural' or herbal deodorant actives described in this review (essential oils such as tea tree and usnic acid, and dozens of herbal extracts) work the same way synthetic actives like triclosan and silver compounds do: by killing or inhibiting the skin bacteria that cause odor, not through some fundamentally gentler mechanism.
Moderate evidence: Based on antibacterial potency (MIC/MBC) data only; this review does not compare skin-irritation or sensitization rates between herbal actives and synthetic anti-microbial salts.
Source: Kanlayavattanakul & Lourith 2011, International Journal of Cosmetic Science Link to this fact
Green, natural and unscented / Measured in people or real products
The unscented 'plain' paraffin candle used as this study's own combustion reference produced the third-highest formaldehyde level of the six candles tested when lit (925 ppb), higher than two of the five scented candles.
Moderate evidence.
Caveats
Single lab, six products, no replication; wax type (paraffin vs. palm) did not track cleanly with formaldehyde output either, so this alone doesn't identify which factor (wax, wick, dye, or fragrance) actually controls it.
Source: Ahn et al. 2015, Journal of Hazardous Materials Link to this fact
Green, natural and unscented / Measured in people or real products
A series of six men's grooming products from one brand were marketed with the text 'Our products never contain artificial colors, synthetic fragrances' while labeled to contain Evernia furfuracea (tree moss) extract, a natural-source fragrance allergen.
Moderate evidence: Single-brand example (n=6 products from one line), not a systematic audit of 'natural' marketing claims.
Source: Bennike 2017/2018 Link to this fact
Green, natural and unscented / Measured in people or real products
Not all fragrance-based odor masking works the same way: Iso E Super, a common deodorant fragrance chemical that barely blocked the malodor receptors in lab dish tests, still reduced how strong a sulfur malodor smelled to people, but less effectively than beta-ionone, suggesting this masking runs mainly through the brain blending two smells together rather than through receptor blocking.
Moderate evidence: Central-processing explanation is the authors' inference from a negative in-vitro result, not directly tested; based on the same single-lab, single-cohort study.
Source: Fukutani et al. 2023, Current Biology Industry-funded Link to this fact
Green, natural and unscented / Measured in people or real products
Ethanol, linalool, and D-limonene, common fragrance and solvent terpenes found in both synthetic and "natural" scented products, were the single most-listed chemicals overall (about 27%, 16%, and 12% of products respectively) in a database of over 7,000 Korean household chemical products, ahead of synthetic fragrance aldehydes like hexyl cinnamaldehyde (about 8%).
Moderate evidence: Ingredient-list prevalence, not measured air or dermal exposure; does not distinguish products marketed as "natural"/"green" from conventional ones.
Source: Lee & Ji 2022, Ecotoxicology and Environmental Safety Link to this fact
Green, natural and unscented / Government agency
EPA's own advice for preventing unpleasant household odors is proper ventilation and basic household cleanliness, not air fresheners or fragranced products.
Moderate evidence: Stated in the context of moth-repellent/paradichlorobenzene odor, not a general product-safety recommendation.
Source: US EPA, "The Inside Story" Link to this fact
Green, natural and unscented / Government agency
Because the EU's expanded fragrance-allergen list includes most of the chemicals that make up common essential oils (lavender, citrus, rose, patchouli, and more), a product marketed as 'natural' or 'essential-oil-based' is not exempt from fragrance-allergen labeling and may in fact trigger more individual allergen declarations than a synthetic-fragrance product.
Moderate evidence.
Caveats
This is an inference from the regulation's own entry list (natural oils named by species as fragrance-allergen entries), not a product-testing study; see our existing natural-cosmetics label surveys for empirical confirmation of a related pattern.
Source: Regulation (EU) 2023/1545 Link to this fact
Green, natural and unscented / Measured in people or real products
A product labeled '100% PURE & NATURAL' (Citrus Magic) and a product labeled 'unscented' (Ozium Glycol-ized Air Sanitizer) both contained phthalates not listed on their labels, in NRDC's 2007 test of 14 air fresheners.
Moderate evidence: Only one all-natural product and one unscented product were tested; not a survey of 'natural'/'unscented' air fresheners generally.
Source: NRDC 2007, Clearing the Air Link to this fact
Green, natural and unscented / Measured in people or real products
In a chamber test of 30 US cleaning products and air fresheners, fragrance-free green cleaners gave off significantly fewer volatile chemicals than conventional ones: about 500 vs 4,700 ug/m3 total on average (approx., read from Fig. 4A), and about 6 vs 46 distinct VOCs per product (approx., read from Fig. 4D).
Moderate evidence.
Caveats
EWG-authored (advocacy nonprofit that ranks cleaners and licenses EWG VERIFIED to cleaner makers); Skyline Foundation grant; unblinded; 7 fragrance-free vs 14 conventional products, one product per brand, single lab; green products also applied less product per use; chamber concentration, not personal exposure. Group means are read from Fig. 4.
Green, natural and unscented / Measured in people or real products
Green cleaners that still contained fragrance were lower than conventional ones on average but not significantly so on total VOC concentration or number of VOCs, so a 'green' label alone was a weaker signal than a fragrance-free one.
Moderate evidence.
Caveats
EWG-authored (advocacy nonprofit that ranks cleaners and licenses EWG VERIFIED to cleaner makers); Skyline Foundation grant; unblinded; 9 green fragranced products; non-significant difference in a small sample is not proof of no difference.
Green, natural and unscented / Other evidence
GOTS 8.1 contains no rule on perfume, scent, or aroma finishes in ordinary clothing; its only fragrance clause (COSMOS criteria) covers Group II personal-care textiles such as tampons and cotton buds, so a GOTS label does not mean fragrance-free clothing.
Moderate evidence: Absence from this document; the Implementation Manual and the Positive List of chemical inputs were not read.
Source: GOTS 8.1 (2026) Link to this fact
Green, natural and unscented / Other evidence
An OEKO-TEX Standard 100 label covers only the as-produced state: the standard says the mark cannot declare anything about harm from "manipulation for sales promotion (e.g. perfuming)", storage or packaging contamination.
Moderate evidence: One standard document; the mark is described as "not a quality label". Whether retailers actually perfume certified goods is not shown.
Source: OEKO-TEX Standard 100 (2026) Industry-funded Link to this fact
Green, natural and unscented / Other evidence
The UK small-animal vets' association warns that people often assume complementary and alternative therapies are natural and therefore safe, but this is not always the case: all therapies may cause side effects or interact with other therapies.
Moderate evidence: General statement with no examples or data; a veterinary professional body's view.
Source: BSAVA position statement on complementary and alternative therapies (reviewed 2024) Link to this fact
Green, natural and unscented / Other evidence
EWG says 'natural' fragrance is not automatically safer than synthetic: the term is unregulated for cosmetics, some natural ingredients are harmful, and it asks natural-fragrance makers to disclose components.
Moderate evidence: Position statement without cited data on this page.
Source: EWG, Skin Deep FAQ (web page, accessed 2026-10-16), EWG web page (Skin Deep FAQ) Link to this fact
Green, natural and unscented / Other evidence
None of 150 "Clean" textured-hair products at a Los Angeles Target listed a chemical on Target's own exclusion list, yet "clean" did not mean fragrance-free: 14.6% listed sulfates and 27% phenoxyethanol.
Moderate evidence.
Caveats
Label reading only. Target's list excludes SLES, not all sulfates, and phenoxyethanol and isothiazolinones were not on it; results for phthalates and formaldehyde are not reported in the text.
Source: Madrid Larrañaga 2026, Journal of Exposure Science & Environmental Epidemiology Link to this fact
Green, natural and unscented / Review of other studies
The paper's neurodevelopment examples involve DEHP, DBP, DiBP and BBzP; it gives no effect size for DEP, the fragrance-associated phthalate, so it does not show that fragranced products affect child brain development.
Moderate evidence: DEP is named only in lists of phthalates reviewed by the CPSC panel and other reviews.
Source: Engel 2021, American Journal of Public Health Link to this fact
Health effects / Self-reported survey
In a national survey of 1,098 Australian adults, one in three (33%) said fragranced products such as air fresheners, cleaners, and perfume gave them health problems, most often breathing trouble, migraines, and skin reactions.
Moderate evidence: Self-report; same dataset as Steinemann 2018 AU asthmatics, 2018 AU MCS, and 2019 AU arm (362/1,098 reconfirmed in the MCS paper's Table 1; not a replication).
Source: Steinemann 2017, Preventive Medicine Reports Link to this fact
Health effects / Self-reported survey
In national surveys of 4,435 adults in the US, Australia, the UK, and Sweden, about 1 in 3 (32%) said fragranced products such as air fresheners, scented cleaners, or other people's perfume cause them health problems.
Moderate evidence: Self-report; any symptom from any product counts; pooled re-analysis of previously published surveys; the US arm (34.7%) is the same dataset as four US papers.
Source: Steinemann 2019, Air Quality, Atmosphere & Health Link to this fact
Health effects / Self-reported survey
About 1 in 8 adults (12.6%) in four countries said fragranced products trigger migraine headaches, and 7% said they trigger asthma attacks.
Moderate evidence: Self-report; no diagnosis check.
Source: Steinemann 2019, Air Quality, Atmosphere & Health Link to this fact
Health effects / Self-reported survey
In a national US survey, about two in three adults with asthma (64.3%) said fragranced products made them ill, compared with about one in four (23.8%) of people without asthma.
Moderate evidence.
Caveats
Self-report, unadjusted; asthma includes undefined 'asthma-like condition'; same dataset as Steinemann 2016; 34% of asthmatics also report diagnosed MCS and 42-53% of affected asthmatics are MCS-diagnosed, but asthmatics without MCS are still affected at 46-56% vs 20-22% of people with neither.
Source: Steinemann 2018, Air Quality, Atmosphere & Health Link to this fact
Health effects / Self-reported survey
27.9% of US adults with asthma said fragranced products had triggered asthma attacks.
Moderate evidence.
Caveats
Self-report. Corroborated but not strengthened by an independent 1986 clinic/inpatient survey (Shim & Williams, n=60, unselected for fragrance sensitivity): 72% named perfume/cologne as worsening their asthma, well above this 27.9% attack-specific representative-survey rate, consistent with our clinic-ceiling-above-population-rate pattern.
Source: Steinemann 2018, Air Quality, Atmosphere & Health Link to this fact
Health effects / Self-reported survey
In a random-based sample of 946 Danish adults, 42% said fragranced products gave them eye, nose, or breathing symptoms in the past year (50% of women, 30% of men).
Moderate evidence: Self-attributed symptoms; sample enriched for allergy at baseline.
Source: Elberling 2005, Clinical and Experimental Allergy Link to this fact
Health effects / Self-reported survey
Among people with symptoms, 56% named other people's perfume, 32% air fresheners, and 28% other people's freshly washed (fabric-softened) clothes as triggers.
Moderate evidence: Self-report.
Source: Elberling 2005, Clinical and Experimental Allergy 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 / Measured in people or real products
Standard allergy tests did not predict who reacted to fragrance; people with sensitive airways (including non-allergic asthma) were 2-4 times more likely to react, pointing to airway irritation rather than classic allergy.
Moderate evidence.
Caveats
Predictors measured 4-5 years before outcomes; association not causation. In clinic patients the reactive trait can be sensory rather than bronchial: Millqvist 1999's 11 perfume reactors were all methacholine-negative and 10/11 skin-prick negative, and Millqvist & Lowhagen 1996's 9 patients (an earlier, blinded, placebo-controlled challenge) were likewise all methacholine-negative yet still reacted significantly to unsmelled perfume with zero objective airway change. So 'sensitive airways' in this literature should not be read as bronchial hyper-reactivity when applied to clinic-referred sensory-hyperreactivity patients; Elberling's population-level BHR association may instead mark co-morbid asthma. A related but distinct 2007 study from the same Gentofte group (Elberling 2007, dermatology-clinic patients, not this population cohort) found a candidate non-IgE, non-neural mechanism in parallel: increased basophil histamine release to perfume, unrelated to atopy, contact allergy, or asthma status. 'Airway irritation' (a neural/sensory account) may not be the whole mechanistic story; BHR, sensory/capsaicin hyperreactivity, and basophil hyperreactivity have not been measured together in the same patients.
Source: Elberling 2005, Clinical and Experimental Allergy Link to this fact
Health effects / Self-reported survey
In a national survey of 1,100 Swedish adults, one in three (33.1%) said fragranced products gave them health problems, most often breathing difficulties (20.0%) and migraines (16.1%).
Moderate evidence.
Caveats
Self-report; same data as 2019 SE arm. A structurally different Swedish research program (Andersson 2008, CSS-SHR instrument) finds a similarly-sized ~33% figure in Skovde adults using a different question ("bothered by strong odors"), cited secondhand within Andersson 2008; that comparator is not yet a primary source in this evidence base, so it corroborates the general phenomenon without directly replicating this claim.
Source: Steinemann 2018 (Sweden), Air Quality, Atmosphere & Health Link to this fact
Health effects / Self-reported survey
In a nationally representative survey of 1,136 US adults, 34.7% said fragranced products such as air fresheners, cleaners, and perfume gave them health problems, most often breathing difficulties, eye/nose irritation, or migraine.
Moderate evidence.
Caveats
Self-report, any symptom from any product; not a diagnosis; adults 18-65 in an opt-in online panel; same US dataset as the 2018 asthmatics, 2018 MCS, and 2019 pooled papers (not replications); 62.7% of the affected also report chemical sensitivity or MCS, but 17.8% of people with neither are still affected.
Source: Steinemann 2016, Air Quality, Atmosphere & Health Link to this fact
Health effects / Self-reported survey
In a national survey of 1,098 Australian adults, more than half of those with asthma or an asthma-like condition (55.6%) said fragranced products made them ill, against about a quarter (23.9%) of people without asthma.
Moderate evidence.
Caveats
Self-report; unadjusted; 'asthma-like condition' undefined (it is 47.9% of MCS respondents in the MCS re-cut); same dataset as the AU arm of Steinemann 2019 and Steinemann 2018 (MCS, AU).
Source: Steinemann 2018, Air Quality, Atmosphere & Health Link to this fact
Health effects / Self-reported survey
About 1 in 4 Australian adults with asthma (24.0%) said a fragranced product had triggered an asthma attack; air fresheners were the most common trigger (14.1% of all asthmatics).
Moderate evidence: Self-report; consistent with US and Danish samples (~34-43% airway symptoms).
Source: Steinemann 2018, Air Quality, Atmosphere & Health 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 / Self-reported survey
In a US national survey, about 1 in 5 adults (20.4%) said air fresheners gave them health problems such as breathing difficulty, migraine, or asthma attacks.
Moderate evidence: Restated from Steinemann 2016 survey; cite the primary; self-report.
Source: Steinemann 2017, Building and Environment Link to this fact
Health effects / Self-reported survey
In a nationally representative survey of 1,100 UK adults, 27.8% said fragranced products such as air fresheners, cleaners, or perfume gave them health problems, including migraines (8.4%) and asthma attacks (6.8%).
Moderate evidence: Self-report, any symptom; same data as Steinemann 2019 UK arm.
Source: Steinemann 2018, Air Quality, Atmosphere & Health Link to this fact
Health effects / Review of other studies
In a small double-blind, randomized lab test (Ternesten-Hasséus 2002, the primary study behind this review's capsaicin-challenge claim), 12 people with multiple chemical sensitivity coughed significantly more than 12 matched healthy controls at every capsaicin dose tested (P<0.05 to P<0.005), a sign that their airway irritant nerves are oversensitive.
Moderate evidence.
Caveats
Now confirmed by reading the primary source directly rather than only via this review's secondhand paraphrase: n=12 patients vs 12 matched controls, single Gothenburg clinic, MCS diagnosed only by Cullen's clinical criteria (no independent biomarker), and not independently replicated outside this same research group (which has authored nearly every paper in this specific evidence line).
Source: Molot 2023, Neuroscience and Biobehavioral Reviews Link to this fact
Health effects / Measured in people or real products
Estimated cancer risks were below one in a million for most feminine hygiene product types; washes (3.3 in a million) and sprays/powders (2.1 in a million) were just above that level under worst-case assumptions.
Moderate evidence: Modeled upper-bound scenario.
Source: Lin 2020, Environment International Link to this fact
Health effects / Lab study (cells or chemistry)
In lab studies, common flavor and fragrance chemicals act directly on TRPA1, the nerve receptor that senses irritants such as mustard oil: cinnamon's cinnamaldehyde and thyme's thymol switch it on, while camphor and eucalyptus oil block it.
Moderate evidence: Cell and animal pharmacology; the review's framing is therapeutic, not hazard.
Source: Mihara & Shibamoto 2015, Allergy, Asthma & Clinical Immunology Link to this fact
Health effects / Measured in people or real products
In a double-blind lab test where people could not smell it, perfume vapor piped to one eye caused more eye irritation than clean air in 10 of 42 people, including 2 healthy volunteers: perfume can irritate the eyes without being smelled.
Moderate evidence.
Caveats
N=42; mostly self-rated eye symptoms; patient vs control difference P=0.07; only 2 objective tearing events. Consistent with the earlier single-blind Millqvist 1999 (eye irritation 1.1 vs 0.2 on 0-3, n=11), a different group, perfume and patient type. Das-Munshi, Rubin & Wessely 2006's systematic review classifies both single-blind Millqvist perfume studies (1996, 1999) as insufficiently blinded (nose clips only, no true olfactory mask), so they should not be counted as strong independent corroboration; Elberling's own double-blind result stands on its own primary data, which is why this stays at moderate rather than strong.
Health effects / Measured in people or real products
The eye irritation from perfume vapor was not an allergy: people patch-test allergic to the very same perfume were no more likely to react than those who were not.
Moderate evidence.
Caveats
21 patients, 10 patch-test positive; small sample. A related 2007 study from the same group, clinic, and challenge perfume found the same pattern in a different assay: basophil histamine release to perfume was not associated with contact-allergy patch-test status either (Table 4, all P > 0.05, n=17 patients). This is modest corroboration from the same research program (same lab/clinic/perfume), not independent replication, so the grade is unchanged.
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
Scent-triggered throat and breathing reactions can mimic asthma but do not respond to asthma inhalers; almost two-thirds of these patients had been prescribed asthma medication anyway.
Moderate evidence.
Caveats
Clinic series; non-response to asthma drugs is the authors' clinical statement, not a trial. Independently corroborated by a different clinic and decade: Millqvist & Lowhagen 1996 (Sweden, 1996) found 7/9 (78%) of its scent-triggered, methacholine-negative patients had been prescribed beta2-agonist and inhaled corticosteroids with 'no demonstrated — but only a subjectively doubtful — effect,' and directly demonstrated the 'mimics asthma' half objectively: perfume provoked significantly more symptoms than saline (P<0.01) with zero change in PEF, O2 saturation, heart rate, respiratory rate, or expired CO2. But like Hoy 2010, the 'does not respond to inhalers' half remains a subjective clinical judgment embedded in a case series in both papers, not a controlled medication trial, so per the grading rule (a claim with any unverified part stays below strong) the grade stays at moderate rather than moving to strong.
Health effects / Measured in people or real products
An older, unblinded human study (Stewart 1970) reported eye, nose, and throat irritation from PGME solvent vapor at 250 ppm in 23 subjects across five experimental runs, and odor tolerance developing within 25 minutes in 6 subjects at 100 ppm; a later double-blind study with objective eye measurements (Emmen 2003) found no objective eye effects at up to 150 ppm and only very slight subjective eye discomfort at 150 ppm, but did not test 250 ppm.
Moderate evidence.
Caveats
Stewart 1970 (read directly) used 23 subjects across five experimental runs at ~230-250 ppm for 1-7 hours (not 'two subjects' as this claim previously stated; the 2-subject figure applies only to a separate rising-concentration ramp experiment used for the 50-75 ppm odor-objectionable and 1000-2050 ppm severity findings) and 6 subjects at 100 ppm, with eye/nose/throat irritation developing in 20 of 23 subjects within 45-60 minutes at 250 ppm. The design remains genuinely unblinded (no placebo condition or masking anywhere in the paper) and reports no objective ocular measurements (redness, corneal thickness, blink counts) — only visual acuity, coordination, neurological, and brake reaction-time tests, all normal throughout at and below 250 ppm. One author (Torkelson) was a Dow Chemical employee and the test material was Dow-supplied ('Dowtherm 209'), a more direct link than Emmen 2003's Dow-supplied sample alone; since the finding (irritation at 250 ppm) runs counter to the sponsor's commercial interest, the COI does not obviously bias this particular result toward understatement. Emmen 2003 did not test 250 ppm, so it does not directly refute the finding, only the confidence one can place in an unblinded, non-objective design; per our grading rule, a single unblinded single-lab study without objective measures cannot reach 'strong' even with n=23.
Source: CIR 2008 (citing Stewart 1970), International Journal of Toxicology Industry-funded Link to this fact
Health effects / Animal study
Citronellol, a rose-scented fragrance ingredient present in about half of household products, crosses the blood-brain barrier: brain-to-blood ratios were 0.5-0.8 in fish, up to 0.6 in mice, and 0.77 in a laboratory barrier built from human brain cells.
Moderate evidence: BBB crossing is measured and dose-independent as a property, but the doses used were far above consumer exposure; routes were waterborne and oral, not inhalation or skin.
Source: Kim 2024, Journal of Hazardous Materials Link to this fact
Health effects / Animal study
At high doses in zebrafish and mice, citronellol pushed tryptophan metabolism toward 3-hydroxykynurenine, a neurotoxic metabolite, and produced brain inflammation, roughly double the oxidative stress, a five-fold rise in dying brain cells, a leaky blood-brain barrier, and anxiety-like behavior.
Moderate evidence: Zebrafish 2-8 mg/L in water; mice 345-3450 mg/kg by gavage (top dose = an LD50); 10^5-10^6 times estimated human exposure; male mice only.
Source: Kim 2024, Journal of Hazardous Materials Link to this fact
Health effects / Animal study
Citronellol's effect on the brain reverses with dose: protective in a rat Parkinson's-disease model at 25 mg/kg oral (given as a month-long pretreatment before each day's toxin dose, not as treatment of existing damage), damaging at 345 mg/kg and above in a different paper, species and route.
Moderate evidence.
Caveats
Both dose points are single-dose, single-model animal work. The protective study (Jayaraj 2022) has now been read directly rather than via Kim 2024's citation and confirms the 25 mg/kg number exactly, but that dose is itself 10^4-10^5x above estimated human citronellol exposure (1,600-8,000x after allometric human-equivalent-dose scaling) — so neither the protective nor the toxic limb has been shown near a human-relevant dose, and the crossover point between 25 and 345 mg/kg remains unmeasured.
Source: Kim 2024, Journal of Hazardous Materials Link to this fact
Health effects / Review of other studies
Salicylate fragrance chemicals pass through skin and are converted in the body to salicylic acid, the compound aspirin becomes: for methyl salicylate (wintergreen), human studies found roughly 12-30% of an applied dose absorbed.
Moderate evidence.
Caveats
Human absorption data are almost all for methyl salicylate, often under occlusion at pharmaceutical concentrations; the review quotes the range three different ways (2-43%, 12-30.7%, 11.8-30.7%).
Source: RIFM Expert Panel / Belsito 2007, Food and Chemical Toxicology Industry-funded Link to this fact
Health effects / Animal study
Mice breathing the vapor of five ordinary commercial colognes for one hour showed airway irritation and a 30-35% drop in mid-expiratory airflow, despite never having been exposed to any allergen or asthma trigger.
Moderate evidence.
Caveats
Mouse study; vapor load never measured and far above household exposure; classical RD50 endpoint was not significant; unreplicated outside the authors' own laboratory. Their 1997 air-freshener study (same two authors, same commercial lab, same computerized ASTM E-981 method, different product) found a matching ~35% peak airflow fall, which is within-lab consistency, not independent replication, and that paper's own 'real-use exposure' claim does not survive comparison with measured indoor VOC data. An independent EPA/ManTech attempt to replicate this lab's method (Tepper et al. 1995, carpets, full text now in our evidence base) found no significant carpet-related toxicity by individual-animal statistics and attributed the lab's positive-looking signals to restrained-exposure procedural stress present even in air-only controls, but it never measured the airflow-limitation endpoint this claim rests on, so it bears on the lab's method credibility generally without directly retesting this specific finding.
Source: Anderson & Anderson 1998, Archives of Environmental Health Link to this fact
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
Many people with chemical sensitivities delay or avoid medical care because clinics and hospitals are heavily scented; healthcare was named as one of the least accessible settings (31 of 60).
Moderate evidence: Qualitative, self-selected Canadian sample; frequency of care avoidance not quantified.
Source: Roy 2026 Link to this fact
Health effects / Self-reported survey
In a nationally representative German survey, half of the people who get sick from fragranced products (51.1%) had been kept from going somewhere because of fragrance, and 43.8% had avoided public toilets with air fresheners or scented products.
Moderate evidence: Self-report; Germany 2019, n=219 fragrance-sensitive of 1,102; same data as Steinemann & Klaschka 2019.
Source: Klaschka 2020, Environmental Sciences Europe Link to this fact
Health effects / Review of other studies
Fragrance can cause skin allergy without touching your own products: from a partner's toiletries (consort dermatitis), from soap residue carried on the hands to the eyelids, and through the air, as in a small case series of a ride-share driver and four passengers whose airborne facial/eyelid dermatitis (all patch-test positive for fragrance mix I and/or balsam of Peru) was linked to car fragrance diffusers, with the driver's rash clearing when his diffuser was removed.
Moderate evidence.
Caveats
Mechanisms from case reports and a systematic review of consort ACD cited by the review; the airborne example is now confirmed against its primary (Perper 2017, now ingested): actually 5 total patients (1 driver + 4 passengers), not just the driver, published in a Contact Dermatitis section the journal states is exempt from mandatory peer review, with no chemical/air testing, no controls, and diffuser-removal resolution documented only for the driver. Kept at moderate, not raised to strong, per the single-small-uncontrolled-study rule; no prevalence data.
Health effects / Lab study (cells or chemistry)
In lab tests on human cells, both lavender oil and tea tree oil switched on estrogen-receptor signaling (about half the maximum effect of the body's own estradiol) and blocked testosterone-type (androgen-receptor) signaling by 41–52%.
Moderate evidence.
Caveats
Cell assays with whole commercial oils at ~0.005–0.025% vol/vol; no data that such concentrations reach a child's body; linalool and linalyl acetate alone were inactive in later guideline assays (industry).
Source: Henley 2007, New England Journal of Medicine Link to this fact
Health effects / Lab study (cells or chemistry)
Lavender oil and tea tree oil activated the human estrogen receptor in cell assays to about 17-18% of the response to estradiol, and blocked testosterone signaling more completely than flutamide, a prescription anti-androgen drug.
Moderate evidence.
Caveats
Human cell lines, oils at 0.005-0.025% v/v; percentages are relative to 1 nM estradiol or 1 nM testosterone in transfected HepG2 and MDA-kb2 cells; Henley 2007 reported ~50% for the same oils in a different cell system.
Source: Ramsey 2019, The Journal of Clinical Endocrinology & Metabolism Link to this fact
Health effects / Review of other studies
If a young child has unexplained early breast development, it is reasonable to ask about lavender and tea tree products, including room diffusers, and try stopping them – which is what the study's authors recommend to doctors.
Moderate evidence: This is the authors' clinical recommendation, not a proven treatment; they explicitly state they are not recommending that anyone avoid these products generally.
Source: Ramsey 2019, The Journal of Clinical Endocrinology & Metabolism Link to this fact
Information, not medical advice. See also: myths we won’t tell you.