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.
Skin allergy / Lab study (cells or chemistry)
In lab tests on human skin cells, the air-oxidized forms of limonene and linalool (the forms that cause fragrance allergy) damaged the fats in cell membranes at concentrations from 100 µM, with oxidized limonene strongest; a possible second route to skin inflammation not yet shown in people.
Weak evidence: Cell line and liposomes only; added iron; real skin doses unknown.
Skin allergy / Review of other studies
A 2007 clinical review reports that oxidized limonene caused positive patch-test reactions in about 2.6% of dermatitis patients in a European study, leading to a call to add oxidized limonene to routine allergy screening.
Weak evidence.
Caveats
Secondary relay of Matura et al. 2006 (not independently read in this evidence base); this is an early statement of a position later found by other groups (e.g. the IVDK) to over-call weak/doubtful reactions as true allergy.
Source: Brasch 2007, Current Opinion in Allergy and Clinical Immunology Link to this fact
Skin allergy / Review of other studies
Axillary dermatitis can occasionally be caused by systemic contact dermatitis or symmetrical drug-related intertriginous and flexural exanthema (SDRIFE) rather than direct topical contact allergy; in sensitized patients, eating balsam-of-Peru-rich foods (citrus, chocolate, tomato, certain alcohols) can trigger a flare without any new topical exposure.
Weak evidence: Relayed from isolated case reports; systemic contact dermatitis of the axillae is described as rare.
Source: Musicante 2024, Cutis Industry-funded Link to this fact
Skin allergy / Other evidence
Across three chemical-intolerance case studies with symptom improvement tied to reduced VOC exposure, blood IgE allergy panels for 16 common indoor/outdoor/food antigens did not track or explain the symptom changes, and only 2 of the full 37-patient cohort (5.4%) had elevated antibodies to both dust mite and cockroach allergens.
Weak evidence.
Caveats
Uncontrolled case-series observation; absence of IgE elevation does not rule out other allergic or non-IgE immune mechanisms, and the paper does not test a specific non-allergic mechanism directly.
Source: Rincón et al. 2024, Primary Health Care Research & Development Link to this fact
Skin allergy / Review of other studies
Standard fragrance-allergy patch screening (fragrance mix I plus balsam of Peru) is estimated to identify only 60 to 70 percent of people with true fragrance allergy, due to the evolving ingredient mix used by the perfume industry.
Weak evidence: Secondhand figure relayed from the authors' ref. 11 (a NACDG/Scheman source), not independently verified or re-derived in this paper.
Source: Zirwas & Moennich 2008, The Journal of Clinical and Aesthetic Dermatology Link to this fact
Skin allergy / Other evidence
Healthcare workers (medicine, dentistry, nursing, veterinary) had the highest fragrance-mix allergy rate among the occupations the London authors analyzed, about 10-12%, which they link to frequent hand washing followed by moisturizers and fragranced medicaments.
Weak evidence.
Caveats
Small groups (154 men), clinic patients; the hand-barrier explanation is the authors' suggestion, not tested; occupation subset tables for retired persons and students contain apparent transcription slips.
Source: Buckley 2003, British Journal of Dermatology Link to this fact
Skin allergy / Other evidence
Part of the US-Europe difference in releaser allergy is artifact: the authors estimate US patch-test positivity runs about 1.4 times higher on average for protocol and referral reasons, and extra US formaldehyde allergy explains more, but quaternium-15 stays about 4.65% vs 1.1% unexplained.
Weak evidence: Rests on an unpublished 20-allergen comparison by the authors and rough arithmetic corrections; exposure, concentration and test-dose explanations were not tested.
Skin allergy / Other evidence
MI in wall paint has caused occupational allergy in painters (5 of 11 occupationally exposed allergic patients in one Danish series) and airborne contact dermatitis in two home owners, one of whom could not stay in his house for 3 weeks after painting.
Weak evidence: Two consumer cases from the authors' own clinic and a series of 37 patients; no air measurements.
Source: Lundov 2011, British Journal of Dermatology Link to this fact
Skin allergy / Other evidence
The US-Europe gap in formaldehyde and releaser allergy (US about 8-9% for formaldehyde vs 2-3% in Europe) may partly reflect US testing at 2% rather than Europe's 1%, as well as different laws; this Spanish series did not test the explanations.
Weak evidence: Authors' speculation; they also cite evidence that the share of cosmetics containing releasers is similar in the US and Europe.
Skin allergy / Other evidence
Fragrance mix I allergy is not reliably lifelong: in the Odense cohort 0 of 11 adolescent reactions were reproduced 15 years later, while clinic patients retested over 1991-2002 reproduced 62% (cited by the authors).
Weak evidence: The 62% clinic figure is cited, not primary here; the cohort result covers one marker (FM I) and says nothing about other fragrance chemicals such as oxidized linalool or limonene.
Source: Mortz 2013, British Journal of Dermatology Link to this fact
Skin allergy / Other evidence
Propylene glycol appeared in more than 37% of 4,674 products in the Society's 2016 Contact Allergen Management Program database, yet whether a positive patch test means allergy or irritation is debated.
Weak evidence: Product-database count is relayed from the Society's own database; relevance of positive patch tests is explicitly debated.
Source: Militello 2020, Dermatologic Clinics Link to this fact
Skin allergy / Other evidence
Danish allergy centers reported textile-dye allergy as rare: 2 of 1,000 Danish skin-ward patients tested in six months had dye-caused allergic eczema, against 'not unusual' 50 of 1,000 in Italy, and cases were mostly with new, unwashed clothes.
Weak evidence: Centers' own account relayed by the report; no data table, definition of case or testing method given; Italian comparison is a verbal statement.
Source: Danish EPA 2014, Survey of Chemical Substances in Consumer Products No. 129 Link to this fact
Skin allergy / Government agency
In the NARC-commissioned model, the sick-day inputs assume people with a fragrance allergy diagnosis are off work 5.6 days a year and people without one 2.1 days.
Weak evidence.
Caveats
Both numbers come from a Danish eczema cohort (Saetterstrom 2014). The report measured no sick leave in fragrance allergy, and the cost model is sensitive to them (one day more or less changes one case's cost by about 5%).
Source: COWI 2019 Link to this fact
Skin allergy / Other evidence
In Denmark, about 70% of recognized occupational contact dermatitis cases are attributed to irritant exposures and 30% to allergy; other occupational series cited in the review give 75% (Saarland notifications) and 57% (Northern Bavaria, plus 15% combined).
Weak evidence.
Caveats
Shares for compensated or notified cases in two countries, not a general rate; ICD is an exclusion diagnosis whose criteria include irritant exposure, which may inflate the irritant share in high-exposure jobs; cited by the review, not measured by it.
Source: Jacobsen 2022 Link to this fact
Skin allergy / Other evidence
In the manufacturer's own pooled patch tests, the rate of skin reactions to sunscreens with 1-6% oxybenzone did not rise with the oxybenzone concentration, and photoallergy tests and standard repeat patch tests gave the same low rate (about 0.27% vs 0.26%).
Weak evidence: Sponsor-held data from healthy adults; per-formula averages, not pooled individual data; the null concentration trend spans only 1-6% with most formulas at 6%.
Source: Agin 2008 (oxybenzone HRIPT), Photodermatology, Photoimmunology & Photomedicine Industry-funded Link to this fact
Skin allergy / Other evidence
After Denmark's nickel regulation, the link between nickel allergy and hand eczema in young women disappeared (OR 3.63 in 1990 to 0.65 in 2006 for women aged 18-35).
Weak evidence: Two cross-sectional surveys by the review's own authors, with wide confidence intervals (1.33-9.96 and 0.29-1.46); cause and effect not established.
Skin allergy / Other evidence
If you have recurring hand rashes, see a dermatologist and ask about patch testing, because in a 15-year Swedish follow-up cited by the review, contact allergy (including nickel allergy) was linked to hand eczema that persisted.
Weak evidence: Weak, single-survey evidence; patch testing advice is general good practice rather than a finding of this review.
Skin allergy / Measured in people or real products
The allergy rate to HICC (a synthetic lily-of-the-valley scent) was 2.1% overall and fell from 2.8% in 2011 to 1.4% in 2014 before rising to 1.8% in 2015; the authors could not say whether exposure changed.
Weak evidence: Single clinic, age and sex standardized, yearly samples of about 950 patients; no exposure data.
Skin allergy / Other evidence
US dermatologists added jasmine and peppermint to the extended allergy panel even though reactions are less common than to other fragrances, because both are also used as flavorings (e.g., peppermint in toothpaste causing lip inflammation).
Weak evidence: Rationale rests on case reports and cited reviews; the paper gives no prevalence numbers for either.
Skin allergy / Review of other studies
A 2004 review by Unilever and London clinic authors concluded benzalkonium chloride (a common preservative and disinfectant) is a clear skin irritant and that many reports of allergy to it are probably irritant patch-test reactions misread as allergy.
Weak evidence.
Caveats
Opinion-based review with no search method; two of four authors worked at Unilever, which sells surfactant-containing products, and no funding statement is printed. Later clinic series (Mayo, Boston, Melbourne) disagree on how much is true allergy.
Source: Basketter et al. 2004, Contact Dermatitis Industry-funded Link to this fact
Skin allergy / Other evidence
When 1,775 patients were patch tested with 0.1% benzalkonium chloride (the routine concentration), the cited German study found more irritant than allergic reactions, and the review's authors suggest true allergy may show only at 0.01%.
Weak evidence.
Caveats
Secondhand relay of an older German-language series; the review gives no counts of irritant versus allergic reactions. A later study cited elsewhere in our evidence base found 0.1% may miss real allergy, so the best concentration is unsettled.
Source: Basketter et al. 2004, Contact Dermatitis Industry-funded Link to this fact
Skin allergy / Other evidence
If a patch test says you are allergic to benzalkonium chloride, ask for a repeat test or a use test of the actual product before concluding it is an allergy, since irritation can look the same.
Weak evidence: Clinical advice from an industry-affiliated review; not a test of outcomes.
Source: Basketter et al. 2004, Contact Dermatitis Industry-funded Link to this fact
Skin allergy / Other evidence
Benzyl alcohol usually causes delayed (type IV) contact allergy, with eczema, papules or vesicles, but less often it can cause immediate reactions (hives, angioedema) after exposure.
Weak evidence: Immediate reactions rest on a few case reports; the review does not separate allergic from nonimmunologic urticaria.
Source: Zheng et al. 2026, ACDS Allergen of the Year (Cutis), Cutis Link to this fact
Skin allergy / Other evidence
Plaster of Paris allergy is very rare: the authors found only seven earlier English-language reports, mostly with Gypsona and positive tests to benzalkonium chloride 0.1%.
Weak evidence: Rarity of reports is not rarity of reactions; the search is not systematic and is from 2000.
Source: Wong and Watson 2001, Australasian Journal of Dermatology Link to this fact
Information, not medical advice. See also: myths we won’t tell you.