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.
Children and pregnancy / Measured in people or real products
16.5% of children and adolescents patch tested in 9 population studies had a contact allergy, and in Swedish 16-year-olds fragrance (2.1%) was the second most common allergen after nickel.
Strong evidence: Any allergen, not fragrance only; some adolescent studies read too early and underestimate.
Children and pregnancy / Review of other studies
Children exposed to household chemical/cleaning products before birth or in their first year wheeze more often, now replicated in four independent prospective birth cohorts. The founding ALSPAC cohort (UK, n=7,019, Sherriff et al. 2005) found that an 11-product, frequency-weighted prenatal household chemical (TCB) score was significantly associated with persistent wheeze through 3.5 years (adjusted OR 1.06 per unit increase; top-vs-bottom-decile adjusted OR 2.3), but not with transient early or late-onset wheeze; this is the same ALSPAC cohort and composite-score methodology that both Casas 2013 and Mikeš 2019 name as their model. In the Canadian CHILD cohort (n=2,022), frequent use in early infancy was linked to higher odds of recurrent wheeze (adjusted OR 1.35) and asthma diagnosis (adjusted OR 1.37) by age 3, but not isolated skin-prick allergy (adjusted OR 1.14, ns), though wheeze combined with allergy was itself raised (adjusted OR 1.49). In the Czech ELSPAC-CZ cohort (n=3,411), each 1-SD increase in an 18-product household chemical exposure score at 6 months raised the odds of intermediate-onset transient, intermediate-onset persistent, and early-onset persistent wheeze phenotypes through age 5 (adjusted OR 1.23-1.36), and those persistent phenotypes carried 5-8x higher odds of doctor-diagnosed asthma at age 7 (pediatrician records, not self-report). In the pooled Spanish INMA cohorts (n=2,292), prenatal (third-trimester) use of cleaning sprays raised the odds of both wheezing (OR 1.37) and lower respiratory tract infection (OR 1.29) in the first year of life, with solvents raising wheezing odds (OR 1.30) and air fresheners raising LRTI odds (OR 1.29); bleach, ammonia, and non-spray cleaners showed no association.
Strong evidence.
Caveats
All four cohorts are observational and use self-reported product-use frequency, not measured indoor air chemistry. The ALSPAC/Sherriff 2005 and ELSPAC-CZ signals are specific to persistent-type wheeze phenotypes, not wheeze in general; ALSPAC found no association with transient early or late-onset wheeze. The 'not atopy' finding remains single-cohort (CHILD only); ELSPAC-CZ's atopic-rash variable is a covariate, not an outcome, and Casas 2013 measured neither atopy nor a physician asthma diagnosis, only maternal-reported LRTI and any-wheezing through 12-18 months, so it neither confirms nor refutes the atopy finding; ALSPAC/Sherriff 2005 did not assess atopy or asthma at all. Casas 2013 is the only cohort among the three post-2010 cohorts with genuinely prenatal (rather than early-postnatal) exposure measurement, but ALSPAC/Sherriff 2005 is also prenatal and its composite score behaved like CHILD's and ELSPAC-CZ's (significant), not like Casas's (null) — evidence against prenatal timing per se explaining the Casas null. Casas 2013's own summed cleaning-product-count score was NOT a significant predictor, unlike ALSPAC's, CHILD's, and ELSPAC-CZ's frequency-weighted composite scores — an open methodological tension (register entry C262) that means 'more products used' is not yet a uniformly replicated exposure metric across all cohorts, even though several specific products (sprays consistently, plus solvents and air fresheners) are.
Source: Salonen 2024, Environment International Link to this fact
Health effects / Government agency
The EU committee said in 2012 that one fragrance allergen, HICC, had caused more than 1,500 published allergy cases in a decade and should not be used in consumer products, even at 200 ppm, and that voluntary industry reductions were insufficient.
Strong evidence.
Caveats
Case counts come from published literature and are described as a severe underestimate; the 'voluntary restrictions are insufficient' judgment is the regulator's reading of available evidence; industry's counter-position is not presented in this document.
The industry / Lab study (cells or chemistry)
The lab tests that replaced animal testing for setting cosmetic and fragrance allergy safety limits explain only about 62% of how strongly a chemical causes allergy.
Strong evidence.
Caveats
Regression R2 against mouse LLNA, not human outcomes; industry-authored. Natsch 2023 (same author) retrains against human-anchored data: the 62% figure survives on a blended human+LLNA composite (63.4%, n=139), but against strictly human data (n=62) accuracy drops to 32-45%, and even the LLNA itself only reaches 43% predicting human potency — so '62%' should not be read as human-relevant accuracy. Api, Basketter & Lalko 2014 (RIFM's own earlier LLNA-vs-human validation, 57 fragrance chemicals) independently corroborates, by a different metric (categorical concordance, not R2) and seven years earlier, that the LLNA itself is an imperfect human proxy: 76% agreement within half an order of magnitude, but up to ~790-fold mispredicted for salicylates and ~26-42-fold for trans-2-hexenal/methyl-2-nonanoate. Roberts & Api 2018 (same fragrance dataset, direct LLNA-vs-human regression) reports a much higher R2=0.784, but only for a 35-chemical subset that already excludes those 14 known outliers a priori — demonstrating that domain-restricted R2 figures like this one can substantially overstate accuracy on unselected chemistry, a caution that applies to curated NAM training/case-study sets generally, not only to this specific figure.
Source: Natsch & Gerberick 2022, ALTEX Industry-funded Link to this fact
The industry / Lab study (cells or chemistry)
Accuracy has not improved: a 2015 model predicted allergy potency about as well as the 2022 one.
Strong evidence.
Caveats
Confirmed by reading the 2015 primary directly, not just inferred from one comparison line in the 2022 paper: Natsch 2015 Equation 7 gives R²(adj)=62.3% (Results, not the abstract's rounded 60%), matching 2022's 62% and 2023's 59-65%.
Source: Natsch & Gerberick 2022, ALTEX Industry-funded Link to this fact
The industry / Other evidence
By 1994 the fragrance industry itself had banned or restricted 82 fragrance materials, most because they cause skin allergy and a dozen because they cause skin reactions in sunlight.
Strong evidence: Counts restrictions, not harm rates; limits not printed.
Source: Ford 1994 (RIFM) Industry-funded Link to this fact
The industry / Lab study (cells or chemistry)
The lab tests that replaced animal testing for fragrance and cosmetic allergy limits have been stuck at explaining about 62% of allergy potency since 2015 — the 2015 model and the 2022 model perform the same.
Strong evidence: Regression R2(adj) against mouse LLNA potency, not human outcomes; industry-funded (Givaudan).
Source: Natsch 2015, Toxicological Sciences Industry-funded Link to this fact
The industry / Government agency
A population study widely treated in dermatology literature as independent, EU-style evidence that confirmed dermatologists' fragrance-allergy estimates over the industry's own claims was itself funded by the fragrance industry's own research body, the Research Institute for Fragrance Materials (RIFM) — a funding fact omitted by every earlier secondhand citation of this study.
Strong evidence.
Caveats
The industry-funded study still confirmed the higher, consumer-relevant estimate (1.9% clinically relevant, up from a disputed 'up to 2%') over industry's own 2000 'far lower' claim — the funding did not appear to weaken the result in this case.
Source: Diepgen 2015 (EDEN), British Journal of Dermatology Industry-funded Link to this fact
The industry / Government agency
As of 2021, the EU's cosmetics regulator states directly that it is not yet possible to use the fragrance industry's QRA2 methodology to set a concentration below which a fragrance chemical is unlikely to cause allergy in new users.
Strong evidence: A regulatory verdict on methodology validity, not a finding that current fragrance concentration limits are unsafe; QRA2 remains in industry use for setting IFRA limits regardless.
Laws and loopholes / Government agency
In 2000, EU cosmetics could declare an entire fragrance as the single word 'parfum'; the EU committee noted dermatologists' estimate that up to 2% of people have perfume allergy, against industry's claim that the true figure was 'far lower'. The EDEN population-based patch-test study (Diepgen 2015; n=3,119 patch-tested across 5 European countries) directly confirmed the dermatologists' estimate: 1.9% (95% CI 1.5-2.5) clinically relevant fragrance contact allergy, and 1.8-2.6% for fragrance mix I alone.
Strong evidence.
Caveats
EDEN is the largest general-population patch-test study of fragrance allergy to date and a large, well-controlled multi-country primary (not a single-lab or single-cohort study), which is why this moves to strong. Note EDEN was itself funded by the Research Institute for Fragrance Materials (RIFM), the fragrance industry's own body — the industry-funded study still confirmed the higher, consumer-relevant estimate over the industry's own 'far lower' claim.
Source: SCCNFP 2000 Link to this fact
Skin allergy / Review of other studies
EU scientific advisers (SCCS 2012) list 82 fragrance ingredients as established causes of skin allergy in people.
Strong evidence.
Caveats
Primary now ingested (SCCS/1459/11): 82 = 54 single chemicals + 28 natural extracts on clinical evidence alone, including the 26 labeled in 1999; the count measures reported allergy evidence, not safety.
Source: Kumar 2020 (SCCS 2012), Journal of Cosmetic Dermatology Link to this fact
Skin allergy / Measured in people or real products
The fragrance chemicals most often found in household products were mostly not in the standard fragrance-allergy patch test used at the time: 6 of its 8 chemicals were in 12% of products or fewer.
Strong evidence.
Caveats
Frequency in products is not the same as clinical sensitization rate; FM II and hydroperoxide testing later added. Clinically confirmed in Heydorn et al. 2003 (n=658 hand-eczema patients, 3 centers): only 3 of the 14 chemicals selected from this paper's household-product survey were FM I constituents, and FM I caught only 45.5% of the fragrance-allergic patients (5.6% of all patients tested missed). The exposure-frequency leader, limonene (78% of products), caused only 0.8-0.9% oxidized-limonene reactivity clinically — product frequency of a chemical still does not predict its clinical allergy rate.
Source: Rastogi 2001, Contact Dermatitis Industry-funded Link to this fact
Skin allergy / Measured in people or real products
Common scent chemicals such as linalool hardly cause allergy when fresh, but once exposed to air they form new chemicals that do: in 1,511 dermatitis patients at six European clinics, 1.3% were allergic to air-oxidized linalool (later studies with a stronger test found about 7%).
Strong evidence.
Caveats
Dermatitis patients, not general population; 2005 test concentration (2.0% pet.) was later shown too low. Clinical relevance no longer just inferred: Andersch Björkman 2014 (ROAT) shows patients identified this way go on to develop dermatitis from twice-daily use of a cream/perfume containing oxidized linalool at concentrations as low as 0.3% (0.056% linalool hydroperoxides, ~27 µg/cm²) — inside the 0.1–2% range measured for individual fragrance ingredients in real products.
Skin allergy / Measured in people or real products
Fresh limonene and linalool rarely cause allergy; the allergens form when these chemicals react with air, which also happens in essential oils and perfumes during storage.
Strong evidence.
Caveats
A '0.1-0.3% of patients' figure was removed because it does not trace to a source in our evidence base. Parent-compound sensitization rates are low but vary by dataset; see the Dittmar 2019 entry for oxidized-terpene positive rates.
Source: Bråred Christensson 2016, Contact Dermatitis Industry-funded Link to this fact
Skin allergy / Measured in people or real products
60.5% of patients allergic to oxidized linalool would never have learned they had a fragrance allergy from the standard fragrance patch tests.
Strong evidence: Dermatitis patients.
Source: Christensson 2012, Contact Dermatitis Link to this fact
Skin allergy / Review of other studies
Standard allergy tests with fresh limonene and linalool miss most of these allergies, so European experts now recommend adding the oxidized forms to routine patch testing.
Strong evidence.
Skin allergy / Review of other studies
Scent chemicals such as limonene and linalool rarely cause skin allergy when fresh, but once exposed to air they form much stronger allergens; products and oils kept open or stored a long time can contain more of them.
Strong evidence.
Caveats
Review of experimental and clinical work; no new data. Hydroperoxide content depends on storage, light, air exposure and antioxidants; no study here shows that a product's age alone predicts content, so do not claim 'older means worse'.
Source: Karlberg & Lepoittevin 2021, Contact Dermatitis Link to this fact
Skin allergy / Measured in people or real products
After nickel, the standard fragrance allergy test (Fragrance Mix I) was the most common positive in the general population: about 3.5% reacted, across 19 studies and 19,440 people.
Strong evidence: Pooled 1966-2017 (CI 2.1-5.4%); the largest modern study found 1.8-2.6% for the same test.
Skin allergy / Review of other studies
The standard fragrance patch test covers only 8 of the 82 fragrance chemicals known to cause allergy in people, so any single test undercounts fragrance allergy.
Strong evidence: Authors' discussion; oxidized limonene/linalool never tested in a general-population sample.
Skin allergy / Measured in people or real products
Among about 4,100 North American patients referred for allergy patch testing in 2019–2020, 12.8% reacted to the standard fragrance mix and 11.1% to oxidized linalool, both among the ten most common skin allergens and both up from 2017–2018.
Strong evidence: Referral population, not the general public; primary is DeKoven 2023 (NACDG), cited by the review.
Skin allergy / Measured in people or real products
The industry's safety panel cleared linalool, a lavender-scented chemical in most fragranced products, as raising 'no safety concerns' after testing the fresh chemical; independent clinics later found that air-exposed (oxidized) linalool causes allergic reactions in about 7% of patients patch-tested for skin allergy (2,900 patients in 9 centers; 5,773 in Sweden, with rates rising).
Strong evidence: Clinic rates are in dermatitis patients, not the general population; test preparations debated; fresh linalool is genuinely a weak sensitizer.
Source: Bickers 2003 (RIFM Expert Panel), Regulatory Toxicology and Pharmacology Industry-funded Link to this fact
Skin allergy / Measured in people or real products
In a patch test of 3,119 people randomly sampled from the general population of five European countries, 2.6% tested positive to fragrance mix I and 1.9% to fragrance mix II, and 1.9% had a fragrance allergy judged clinically relevant (skin symptoms plus product avoidance).
Strong evidence.
Caveats
The largest, best-controlled general-population fragrance patch-test study to date (n=3,119 of 12,377 interviewed, harmonized protocol across 5 countries); the raw marker-positive rate is higher (4.1%) before the clinical-relevance filter, and about half of marker-positive people do not meet the stricter definition.
Source: Diepgen 2015 (EDEN), British Journal of Dermatology Industry-funded Link to this fact
Skin allergy / Measured in people or real products
In a 5-year Danish patch-test survey of 17,716 eczema patients, 10.1% had fragrance allergy, and cosmetic products caused 42.1% of it; deodorants (25.3% of specific products listed) and scented lotions (24.4%) were the two leading culprits, together accounting for roughly half of all cases.
Strong evidence.
Caveats
Clinic-referred eczema patients (Danish Contact Dermatitis Group members' consecutive patients), not a general-population sample; retrospective database analysis, not a prospective cohort.
Source: Heisterberg 2011, Contact Dermatitis Link to this fact
Skin allergy / Measured in people or real products
Deodorants were significantly more likely to be the reported cause of fragrance allergy in men than women (37.9% vs 21.1% of listed products, odds ratio 2.3), while scented lotion (odds ratio 2.6) and fine fragrances (odds ratio 4.2) were significantly more often the reported cause in women; shampoo showed no sex difference.
Strong evidence: Reflects differential product use by sex, not necessarily differential susceptibility to sensitization.
Source: Heisterberg 2011, Contact Dermatitis Link to this fact
Skin allergy / Measured in people or real products
Standard fragrance allergy screening tests (the fragrance mixes, HICC, Myroxylon pereirae, colophonium) missed about 70% of patients allergic to oxidized limonene or linalool; only 30-33% of hydroperoxide-allergic patients also reacted to any standard baseline marker.
Strong evidence: None.
Source: Deza 2016, Contact Dermatitis Industry-funded Link to this fact
Skin allergy / Measured in people or real products
Women's overall contact allergy rate (35.5%) was roughly double men's (17.1%) in this general-population sample.
Strong evidence: OR 2.6 (95% CI 2.1-3.1) adjusted for age and skin complaints; nickel allergy (much more common in women, 22.2% vs 5.2%) drives most of the gap.
Source: Diepgen 2016 (EDEN), British Journal of Dermatology Industry-funded Link to this fact
Skin allergy / Review of other studies
Fragrance ingredients rank alongside nickel as a leading cause of contact allergy in dermatology-clinic eczema patients, diagnosed in roughly 10-12% of those tested.
Strong evidence: Clinic (patch-tested, already-eczematous) populations, not the general population; figures are for FM I specifically.
Source: Johansen 2003, Am J Clin Dermatol 4(11):789-798, American Journal of Clinical Dermatology Link to this fact
Skin allergy / Measured in people or real products
In a 2018 meta-analysis pooling 28 general-population patch-test studies (20,107 people), the pooled prevalence of contact allergy to Myroxylon pereirae (balsam of Peru) was 1.8% (12 studies, 8,002 people, 95% CI 1.0-2.7%).
Strong evidence.
Caveats
Meta-analysis with substantial heterogeneity across the 12 pooled studies (I2 85.3%); general-population samples, not clinic-referred dermatitis patients, so this is a lower-bound estimate compared to referred populations.
Skin allergy / Government agency
In 2012 the EU's scientific committee on consumer safety (SCCS) classified 82 fragrance ingredients (54 chemicals and 28 natural extracts, including all 26 then labeled) as established causes of contact allergy in people, on clinical evidence alone.
Strong evidence.
Caveats
Counts reported patch-test and case-report evidence from the literature to October 2010; many counts rest on small or single-center series and publication bias; the classification measures allergy evidence, not a safe-use verdict.
Children and pregnancy / Measured in people or real products
The protective association between bleach cleaning and reduced allergy/asthma risk was abolished in households with parental smoking; in that subgroup, bleach use was instead linked to a higher rate of recurrent bronchitis (adjusted OR for the smoking-by-bleach interaction, 2.03, 95% CI 1.12-3.66).
Moderate evidence: Subgroup/interaction analysis from a single cross-sectional study; the recurrent-bronchitis outcome is parent-reported, not medically confirmed.
Source: Nickmilder, Carbonnelle & Bernard 2007, Pediatric Allergy and Immunology Link to this fact
Children and pregnancy / Other evidence
Fragrance contact allergy is not rare in children: in a study of 1200 Danish school children aged 12-16, 1.6% of girls and 2.1% of boys tested positive to the fragrance mix, and one in three of them already had clinical symptoms.
Moderate evidence: Single study (secondary citation); the primary (Mortz 2002) is not yet in our evidence base.
Source: Johansen 2003, Am J Clin Dermatol 4(11):789-798, American Journal of Clinical Dermatology Link to this fact
Children and pregnancy / Measured in people or real products
In a UK cohort of 1,303 infants (the EAT study), each additional weekly infant moisturizer application at 3 months of age was associated with an 18-20% higher adjusted odds of developing challenge-confirmed food allergy by age 3 (adjusted OR 1.20, 95% CI 1.13-1.27).
Moderate evidence.
Caveats
Single observational cohort; moisturizer frequency is parent-reported and not randomized, so confounding by indication (e.g., subclinical dry skin) cannot be fully excluded, though sensitivity analyses reduced this concern.
Source: Perkin 2021 (EAT cohort), Journal of Allergy and Clinical Immunology Link to this fact
Children and pregnancy / Measured in people or real products
The moisturizer-frequency/food-allergy association held both in infants with visible eczema at 3 months (adjusted OR 1.20, 95% CI 1.11-1.31) and in infants with no visible eczema at all (adjusted OR 1.18, 95% CI 1.07-1.30), and survived a reverse-causation sensitivity analysis that excluded infants with any parent-reported history of eczema or dry skin (adjusted OR 1.16, 95% CI 1.01-1.33).
Moderate evidence.
Caveats
Adjusted for study group, sex, siblings, family eczema history, ethnicity, eczema severity (SCORAD), filaggrin mutation status and TEWL, but exposure is still self-reported and non-randomized.
Source: Perkin 2021 (EAT cohort), Journal of Allergy and Clinical Immunology Link to this fact
Children and pregnancy / Measured in people or real products
In the same cohort, bathing frequency at 3 months — despite being strongly correlated with moisturizing frequency — showed no association with later food allergy (adjusted OR 0.95, 95% CI 0.83-1.08), unlike moisturizing frequency itself.
Moderate evidence: A negative-control comparison within one cohort; does not rule out that bathing and moisturizing share some unmeasured common cause.
Source: Perkin 2021 (EAT cohort), Journal of Allergy and Clinical Immunology Link to this fact
Children and pregnancy / Measured in people or real products
In the same trial, infants given daily preventive emollient had a nonsignificant increase in confirmed food allergy to milk, egg, or peanut at age 2 (7% vs 5%, adjusted RR 1.47, 95% CI 0.93-2.33) and food sensitization (12% vs 9%, adjusted RR 1.36, 95% CI 0.94-1.95), measured by oral food challenge (21 of 70 cases) or a masked expert panel using a validated EAT-trial-derived algorithm (49 of 70 cases).
Moderate evidence.
Caveats
Neither the food-allergy nor the sensitization result reached statistical significance; the trial was powered to detect an eczema effect, not a food-allergy effect, so it is likely underpowered for this secondary outcome.
Source: Chalmers et al. 2020 (BEEP trial), The Lancet Link to this fact
Fragrance is everywhere / Measured in people or real products
A lab analysis of 59 soaps, surface cleaners, laundry and dish-washing products from four European countries found the citrus-scent chemical limonene in 78% of them, linalool in 61%, and citronellol in 47%; all three are fragrance chemicals linked to skin allergy.
Moderate evidence: Products c. 2000, EU only; parent terpenes measured, not the allergenic oxidized forms; Unilever co-author.
Source: Rastogi 2001, Contact Dermatitis Industry-funded Link to this fact
Fragrance is everywhere / Measured in people or real products
A 2015 survey of 817 unique detergent products from 131 German households found limonene and linalool — the two fragrance chemicals most often linked to skin allergy when oxidized — named on 23.1% and 20.1% of product labels, more than any of the other 24 EU-declarable fragrance allergens.
Moderate evidence: Label-declaration frequency above the EU's 0.01% threshold, not a chemical measurement; Northern Germany, 2015, convenience sample, not representative.
Source: Wieck 2018, Regulatory Toxicology and Pharmacology Link to this fact
Fragrance is everywhere / Review of other studies
Burning, stinging, or itching sensations in the eyes, nose, and throat from airborne chemicals are caused by a specific, receptor-mediated nerve reflex (activation of TRPV1, TRPA1, TRPM8, and related channels on trigeminal nerve endings), not by allergy or immune response.
Moderate evidence.
Caveats
This is established sensory-irritation physiology synthesized from many primary studies the review cites, not new data from this paper; it describes the receptor mechanism, not whether any specific product or exposure reaches an irritating dose.
Source: Nielsen & Wolkoff 2017, Regulatory Toxicology and Pharmacology Industry-funded Link to this fact
Fragrance is everywhere / Measured in people or real products
Besides the fragrance-mix allergens, 14 other common fragrance materials (including linalool, benzyl acetate, and hedione) were found in 40-97% of the 73 deodorants tested in 1996; for three of them (hedione, linalyl acetate, alpha-isomethyl ionone) no published human contact-allergy case existed at the time despite their widespread use.
Moderate evidence.
Caveats
Absence of published reports as of 1998 is not the same as absence of risk; testing history for these three substances specifically was not systematically reviewed by the authors beyond a literature check.
Source: Rastogi et al. 1998, Contact Dermatitis Link to this fact
Fragrance is everywhere / Measured in people or real products
Because most cosmetics contain fragrance, the dermatologists noted that fragrance allergy is not limited to fragrance products: fragrance ingredients were the commonest allergen group even though perfumes and colognes were only 7% of reactions.
Moderate evidence.
Caveats
Authors' inference from a selected series; 39 reactions were to unspecified fragrance and 77 to individually identified fragrance ingredients, with the 77 not reproducible from the printed table.
Source: Eiermann 1982, Journal of the American Academy of Dermatology Link to this fact
Green, natural and unscented / Animal study
'Natural' doesn't mean allergy-free: essential oils oxidize too; in mouse tests lavender oil exposed to air for 45 weeks became about 8 times more potent as a sensitizer (EC3 36% fresh, 4.4% aged), and oxidized alpha-terpinene from tea tree oil was the most potent of all.
Moderate evidence.
Caveats
Mouse LLNA (groups of 3-4 mice; one 45-week sample) from the primary Hagvall 2008, lab open-flask exposure; aged oil reached 'moderate', not 'strong', potency. Human support: 4/4 oxidized-linalool-allergic patients reacted to oxidized lavender oil (elicitation, n=4). Earlier evidence base figure '11% -> 4.4%' was a misreading.
Green, natural and unscented / Review of other studies
Many products sold as "fragrance free" in natural-product stores are free only of synthetic fragrance and still contain essential oils, which make up 80 of the 162 fragrance ingredients documented to cause skin allergy.
Moderate evidence.
Caveats
80/162 is a count of documented allergens (de Groot), not a risk comparison; the store claim is unquantified. Klaschka 2016 supports the mechanism (supplier SDSs: orange oil ~95% limonene, lavender ~40% linalool) but counted no 'fragrance-free'-labeled products, and in its EU sample 58/100 products did declare natural-origin allergens, so on EU labels the ingredient list often shows them.
Green, natural and unscented / Government agency
Allergy UK's Product Endorsement Scheme is run by Allergy Research Ltd, a private limited company that is a legally separate trading subsidiary of the charity British Allergy Foundation (which operates publicly as Allergy UK); ARL donates its profits to the charity.
Moderate evidence: Organizational/legal fact stated plainly on the page itself; not independently verified against Companies House or charity filings.
Source: Allergy UK 2026 Link to this fact
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
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 / 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 / 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 / Measured in people or real products
Some people whose breathing problems are set off by scents do not have asthma or allergy: in a Swedish clinic study, 11 such patients had normal lung function, negative methacholine and allergy tests, and asthma medicines had given most of them little relief.
Moderate evidence: Clinic referrals selected for scent-triggered complaints; n=11; describes a phenotype, not its prevalence.
Health effects / Measured in people or real products
The extra coughing in multiple chemical sensitivity patients was not explained by asthma or classic allergy: patients tested negative on standard allergy skin-prick and methacholine airway-reactivity tests, and lung function (FEV1) did not change after capsaicin, pointing to an oversensitive airway nerve response rather than an allergic or asthmatic reaction.
Moderate evidence.
Caveats
Small single-center sample; several patients used asthma/allergy medication for symptom control (withheld before testing), so baseline airway status over time is not fully independent of treatment.
Source: Ternesten-Hasséus 2002, Journal of Occupational and Environmental Medicine Link to this fact
Health effects / Measured in people or real products
The excess basophil reactivity to perfume in symptomatic patients was not explained by allergy antibodies in the blood (a passive-serum-transfer test found no difference between groups) and did not track whether a patient also had a skin (contact) allergy, an inhalant allergy, or asthma.
Moderate evidence.
Caveats
Same research group, clinic and perfume as the 2006 eye-challenge study, so this corroborates rather than independently replicates that program's earlier 'not classic allergy' findings.
Source: Elberling 2007, Clinical and Experimental Allergy Link to this fact
Health effects / Measured in people or real products
An individual's sensitivity to a given dose of an irritant gas (sulfur dioxide) was highly reproducible when the same person was retested 1-7 weeks later (r=0.85 across all subjects, r=0.82-0.74 within asthmatic subgroups), even though that sensitivity could not be predicted well from a clinical asthma diagnosis, allergy skin testing, or serum IgE level.
Moderate evidence: Single-lab study, n=85 total; reproducibility was much weaker for exercise responses measured in clean air alone.
Source: Linn et al. 1987, American Review of Respiratory Disease Link to this fact
Health effects / Measured in people or real products
Atopic (allergic, IgE-sensitized) volunteers without asthma were essentially as unresponsive to sulfur dioxide exposure as non-atopic normal volunteers; airway hyperreactivity (asthma), not IgE-mediated allergy/atopy, was what predicted reaction to this irritant gas.
Moderate evidence.
Caveats
Single-lab study, n=21 atopic subjects; sulfur dioxide is a non-allergenic irritant gas, so this speaks to the general atopy-vs-hyperreactivity question rather than to any allergic mechanism for SO2 itself.
Source: Linn et al. 1987, American Review of Respiratory Disease Link to this fact
Health effects / Measured in people or real products
In a small Swedish clinic study, people whose breathing symptoms were triggered by scents and chemical irritants — but who had normal lung function and negative allergy and asthma tests — coughed much more after inhaling capsaicin (the hot-pepper compound) than either people with verified asthma or healthy volunteers (93 vs 23 average coughs at the highest dose, P<0.001).
Moderate evidence.
Caveats
Small (n=10 per patient group, n=28 healthy controls), single-clinic study; capsaicin dosing was open-label (patients not told doses would increase) rather than placebo-blinded, so it is a correlational patient-vs-comparator design, not an intervention.
Source: Millqvist, Bende & Löwhagen 1998, Allergy Link to this fact
Health effects / Measured in people or real products
The extra coughing in these chemically sensitive patients could not be explained by asthma: their lung function, methacholine reactivity, and skin-prick allergy testing were all normal, yet they still coughed dose-dependently to inhaled capsaicin, and even to a plain saline control, while a separate group of people with verified asthma did not cough more than healthy volunteers.
Moderate evidence.
Caveats
Single small clinic sample (n=10 per patient group); normal methacholine and skin-prick tests were inclusion criteria for the chemically sensitive group, not an independent finding in an unselected population.
Source: Millqvist, Bende & Löwhagen 1998, Allergy Link to this fact
Health effects / Self-reported survey
Among the same scented-candle users, respiratory-specific complaints in the past 12 months included waking with chest tightness (36.0%), waking from a coughing attack (33.1%), nasal allergy/hay fever (25.0%), a diagnosed respiratory illness (16.3%), a shortness-of-breath attack on waking (17.2%), wheezing (14.6%) and an asthma attack (9.5%).
Moderate evidence: Self-reported, non-clinically-confirmed symptoms in a non-representative convenience sample; no comparison group of non-candle-users was asked the same respiratory questions.
Source: Al Khathlan et al. 2023, BMC Public Health Link to this fact
Health effects / Other evidence
The 1988 Nature experiment claiming diluted antibody still triggers allergy cells was judged an artifact of observer bias by an investigative team, and independent labs reportedly failed to replicate it.
Moderate evidence: Secondhand and compressed account; Grimes also lists Belon 1999 as a failure although its title reports an inhibition effect; see the Maddox and Davenas pages.
Source: Grimes 2012, Focus Altern Complement Ther, Focus on Alternative and Complementary Therapies Link to this fact
Health effects / Other evidence
Exercise, painkillers (NSAIDs) and alcohol can lower the threshold at which a food triggers anaphylaxis: in 74 cases of cofactor-enhanced food allergy NSAIDs were involved in 58%, exercise in 52.7%, and alcohol in 12.2%.
Moderate evidence: Clinic case series without matched controls; the review reports them and does not re-analyze them.
Source: Skypala 2019, Frontiers in Immunology Link to this fact
Health effects / Other evidence
Daily sunscreen use did not increase skin cancer risk in this 4.5-year randomized trial; the main complaints were contact allergy or skin irritation in 25 of about 800 users, greasiness and sweat interference.
Moderate evidence: Cancer was the safety endpoint studied; no absorption or systemic toxicity was measured; allergen causing the 25 reactions not identified; the sunscreen was supplied by industry.
Source: Green 1999, The Lancet Industry-funded Link to this fact
Health effects / Other evidence
A European allergy-society expert panel says asthma starting within hours of a single very high irritant exposure, such as a chlorine or chloramine cloud from mixing bleach with acids or ammonia, can be attributed to the exposure with a high level of confidence.
Moderate evidence: Expert consensus, not a systematic review; exposure concentrations in the underlying cases were mostly estimated, not measured.
Health effects / Other evidence
Irritant-induced asthma is not an allergy: a single high exposure can trigger it without a sensitization latency period, and affected people do not react to low re-exposure of the same agent, though their airways can stay hyperresponsive for years afterward.
Moderate evidence: Expert consensus; rare cases of true sensitization after accidental exposure to a sensitizer are acknowledged.
Information, not medical advice. See also: myths we won’t tell you.