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.
Skin allergy / Measured in people or real products
In a controlled study, everyone already allergic to limonene hydroperoxides (11/11) developed a skin reaction within about a week of daily exposure to fine-fragrance-level doses of oxidized limonene (140 ppm and up); healthy people (0/17) had no reaction even at the highest dose tested.
Strong evidence: Single multicenter study; 11 allergic subjects and 17 controls.
Skin allergy / Measured in people or real products
In a 2015 survey of 187 US pediatric personal-care products marketed as hypoallergenic, dermatologist-recommended, fragrance-free, or paraben-free, 89% (167/187) contained at least one contact allergen from the standard NACDG screening tray, with a mean of 2.4 allergens per product.
Strong evidence.
Caveats
Single-metro US convenience sample (six unnamed Redlands, CA retailers, 2013), label-based (no chemical verification, no concentrations), and allergen matching by an unaudited custom algorithm; the four marketing-term categories overlap (a product can carry more than one), so subgroup percentages are not independent comparisons.
Source: Hamann 2015, Journal of Allergy and Clinical Immunology 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 clinical study of 658 hand-eczema patients across 3 European centers, 67 (10.2%) reacted on patch testing to at least one fragrance chemical selected because it is common in household cleaning and personal-care products used on the hands.
Strong evidence: Clinic-referred hand-eczema population (3 tertiary centers), not a random sample of the general public.
Source: Heydorn 2003, Contact Dermatitis Industry-funded Link to this fact
Skin allergy / Measured in people or real products
More than half (54.5%) of the hand-eczema patients allergic to household-product fragrance chemicals would not have been identified by the standard Fragrance Mix I patch test alone.
Strong evidence: Applies to this hand-eczema clinic population and this specific 14-chemical panel; FM II (2008) and hydroperoxide testing have since narrowed but not closed the gap.
Source: Heydorn 2003, Contact Dermatitis Industry-funded Link to this fact
Skin allergy / Review of other studies
Oxidized forms of limonene and linalool, formed when these common fragrance terpenes react with air, are now treated as a standard, distinct fragrance-allergen category in mainstream dermatology, alongside fragrance mix I/II and balsam of Peru.
Strong evidence.
Caveats
This 2025 general-ACD review reflects consensus classification, not new prevalence data; primary prevalence numbers should be cited from Sukakul 2022, Bråred Christensson 2016/2012, or the EECDRG review already in our evidence base, not this source.
Source: Aristizabal-Torres 2025, JAAD Reviews 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
In a Spanish study of 3,639 consecutive dermatitis patients at 22 clinics, 5.1% were allergic to oxidized limonene and 4.9% to oxidized linalool, two of the most common fragrance chemicals, at the recommended patch-test concentrations.
Strong evidence.
Caveats
Figures are from a clinic-referred dermatitis population, not a general-population sample; positivity depends heavily on the concentration tested (see next claim), and one major network (IVDK) disputes whether these top concentrations over-call true allergy.
Source: Deza 2016, Contact Dermatitis Industry-funded Link to this fact
Skin allergy / Measured in people or real products
Positive reactions to oxidized limonene and linalool roughly tripled as the patch-test dose increased (limonene hydroperoxides 1.4% to 5.1%; linalool hydroperoxides 1.3% to 4.9% across three concentrations), and about a third to two-fifths of allergic patients would have been missed entirely at the next-lower dose.
Strong evidence.
Caveats
Irritant reactions also rose slightly at the highest doses (up to 1.5-1.9%); whether this dose-response reflects true allergy or growing over-sensitivity of the test material is an open dispute.
Source: Deza 2016, Contact Dermatitis Industry-funded 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
About a quarter of patients allergic to either oxidized limonene or oxidized linalool reacted to both, while three-quarters reacted to only one, supporting that these are two distinct, specific fragrance allergies rather than a single non-specific reaction to hydroperoxide chemistry in general.
Strong evidence: Replicates an earlier international multicenter finding (25.3%/74.7%) in an independent, larger, single-country cohort.
Source: Deza 2016, Contact Dermatitis 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, more than 1 in 4 (27.0%) tested positive to at least one of 32 standard contact allergens; nickel (14.5%) and thiomersal (5.0%) were the most common.
Strong evidence.
Caveats
The largest, best-controlled general-population patch-test study of its kind (n=3,119 of 12,377 interviewed, harmonized protocol across 5 countries); a positive patch test indicates sensitization, not necessarily active dermatitis.
Source: Diepgen 2016 (EDEN), British Journal of Dermatology 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 double-blind study, deodorants containing isoeugenol at concentrations from 0.0063% to 0.2% triggered allergic skin reactions within weeks in 10 of 13 people already allergic to it, while identical unscented deodorants and the same products used by 10 non-allergic people caused no reactions.
Strong evidence.
Caveats
Small cohort (13 sensitized test patients fully tabulated of 35 enrolled), but statistically significant (P<.001) with a concurrent negative control group (0/10) and a randomized, double-blind, contralateral-axilla design; unblinding confirmed the active deodorant caused every reaction.
Source: Bruze et al. 2005, Contact Dermatitis Link to this fact
Skin allergy / Government agency
26 fragrance chemicals must be individually named on EU cosmetic labels once they exceed 0.001% in leave-on products or 0.01% in rinse-off products.
Strong evidence: This is the labeling threshold in force under this 2021 document; a later EU regulation (2023) expanded the allergen list further and postdates this source.
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.
What you can do / Review of other studies
Never mix bleach with ammonia or acidic cleaners: 13 published poisoning reports, including one death, came from mixing products.
Strong evidence: Case reports; not fragrance-related.
Source: Nazaroff & Weschler 2004, Atmospheric Environment Link to this fact
What you can do / Review of other studies
Choosing fragrance-free personal care products is a reasonable way to cut DEP exposure, since DEP is used as a fragrance solvent; label reading alone will not catch phthalates.
Strong evidence: Reasoned advice; not tested as an intervention in this paper.
Source: Crinnion 2010, Alternative Medicine Review Link to this fact
What you can do / Measured in people or real products
If you have unexplained or recurring dermatitis, ask whether patch testing will include oxidized linalool (and oxidized limonene); standard fragrance tests missed 60% of these allergies.
Strong evidence: Hydroperoxide tests now recommended for baseline series in Europe.
Source: Christensson 2012, Contact Dermatitis Link to this fact
What you can do / Review of other studies
Never mix bleach with ammonia or acidic cleaners: it makes toxic chloramine or chlorine gas.
Strong evidence: Established chemistry; review restates it.
Source: Salonen 2024, Environment International Link to this fact
What you can do / Measured in people or real products
Choosing fragrance-free cosmetic and personal care products is an effective way to cut DEP exposure, since fragrance is consistently the most DEP-dense product category across three independent national surveys and DEP is never named on a label when present via fragrance.
Strong evidence: Based on product-content measurement across three independent surveys (Hubinger & Havery 2006, Dodson 2012, Koniecki 2011), not a tested behavioral intervention.
Source: Koniecki 2011, Environmental Research Link to this fact
What you can do / Government agency
Banning or phasing out a single chemical can measurably cut human exposure within a few years: after the US residential ban on the insecticide chlorpyrifos in 2000, New York children's blood levels of it fell significantly within a year and to less than half within two years, and after the US phase-out of leaded gasoline, children's average blood lead levels (NHANES data) fell sharply over the following decade.
Strong evidence: These are well-documented US regulatory case studies (chlorpyrifos, lead); the report does not claim the same speed of decline for every banned or restricted chemical.
Source: WHO/UNEP 2012 Link to this fact
What you can do / Government agency
EPA says to never mix chlorine bleach solution with other cleaning solutions or detergents that contain ammonia, because toxic fumes could be produced.
Strong evidence: Well-established chemistry (chloramine gas formation); stated here as a direct safety instruction, not a study finding.
Source: US EPA, "A Brief Guide to Mold, Moisture and Your Home" Link to this fact
What you can do / Government agency
New Zealand's 2026 cosmetics amendment bans PFAS (per- and polyfluoroalkyl substances) outright in cosmetic products, with a graduated phase-out: import and manufacture of PFAS-containing cosmetics permitted until 31 December 2026, supply until 31 December 2027, and mandatory disposal of remaining stock by 30 June 2028.
Strong evidence: Primary legal text (Schedule 4 Table 2 entry 2, structural PFAS definition; Schedule 2 transitional provisions, clause 4).
Source: Cosmetic Products Group Standard 2020 (NZ, HSR002552, consolidated and current to 1 Jan 2026) Link to this fact
Information, not medical advice. See also: myths we won’t tell you.