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.
Laws and loopholes / Other evidence
Target's "Formulated without Parabens" and "without Phthalates" badges were applied unevenly (27 and 53 qualifying products lacked them), and Target says the badges rely only on manufacturer labels.
Weak evidence: Badge absence is not a false claim, since badges are optional; the 53 figure appears only in the Discussion, and phthalates in fragrance would not show on a label.
Source: Madrid Larrañaga 2026, Journal of Exposure Science & Environmental Epidemiology Link to this fact
Laws and loopholes / Other evidence
Coriander is not among the 14 allergens the EU requires to be declared, so a flavoring spice that triggered anaphylaxis in one patient did not have to be named on the beer label, according to the case report's authors.
Weak evidence: Authors' legal reading, not a legal analysis; one case; the report does not say any rule was broken. Beer labeling rules differ from other foods.
Laws and loopholes / Other evidence
Regulators' leave-on limits for behentrimonium chloride (up to 3.0% in the EU) are supported partly by manufacturer data of this kind rather than independent studies.
Weak evidence: The SCCS also used a margin-of-safety calculation; this paper is one input among several.
Source: Cameron 2013, Toxicology in Vitro Industry-funded Link to this fact
Laws and loopholes / Other evidence
More shoppers cited the Environmental Working Group (23 of 325 comments, 7%) than a dermatologist recommendation (20, 6%) as a reason to buy, but both were rare. The authors say EWG ranks products from manufacturer and toxicology databases without checking how well they protect.
Weak evidence: Tiny counts; the Discussion text gives 22 and 18, and the EWG description is the authors' opinion.
Laws and loopholes / Government agency
EPA's 2017 ADBAC work plan sets a schedule of data call-in in March 2018, data received March 2020, preliminary risk assessments in September 2021 and a final registration-review decision in September 2022, and says it will revise the schedule if needed (for example for endocrine screening).
Weak evidence: A 2017 target schedule only; whether EPA kept to it was not read.
Source: US EPA 2017 Link to this fact
Laws and loopholes / Government agency
The EPA work plan says ADBAC is subject to EPA's Endocrine Disruptor Screening Program but reports no endocrine screening results, and notes that being on a screening list does not mean a chemical is a known or likely endocrine disruptor.
Weak evidence: The document contains no endocrine data; absence of results here is not evidence either way.
Source: US EPA 2017 Link to this fact
Laws and loopholes / Other evidence
The EU acted on benzophenone-3 and octocrylene because both were suspected of endocrine-disrupting properties and were prioritized for review; the SCCS issued opinions in March 2021 and the Commission's draft implemented them.
Weak evidence: Page says only 'suspected'; it is not a finding that either is an endocrine disruptor; consultancy summary.
Source: COSlaw.eu (Obelis) 2022, UV filters news Industry-funded Link to this fact
Laws and loopholes / Other evidence
A person who faces disability discrimination or does not receive appropriate accommodation can file a complaint with the Canadian Human Rights Commission, per the CHRC's 2019 sheet.
Weak evidence: Complaint route is for matters within federal jurisdiction; the sheet reports no outcomes or complaint numbers.
Source: [[src-2019-chrc-environmental-sensitivity-scent-free-policies|CHRC 2019]] Link to this fact
Laws and loopholes / Other evidence
ASEQ-EHAQ, an environmental-health advocacy charity, posted an appeal dated 2022-02-07 stating of a Toronto woman with MCS: "She will die by lethal injection on February 22, 2022 unless she finds healthy housing…", 15 days after the post.
Weak evidence: Advocacy appeal with no documentation or named source; the statement is the charity's. Pre-event page; says nothing about the outcome.
Source: [[src-2022-aseq-ehaq-urgent-help-save-sophias-life|ASEQ-EHAQ 2022]] Link to this fact
Laws and loopholes / Other evidence
ASEQ-EHAQ's appeal says that, instead of being given accessible housing free of VOCs, smoke and mold, she "has instead been approved for medical assistance in dying (MAiD)."
Weak evidence: The charity's framing with no source; it does not say who approved it, when, or under which legal pathway.
Source: [[src-2022-aseq-ehaq-urgent-help-save-sophias-life|ASEQ-EHAQ 2022]] Link to this fact
Laws and loopholes / Other evidence
CTV reported that her assisted death "appears to be a first in the world" for someone diagnosed with MCS, according to patient support groups and doctors familiar with her case.
Weak evidence: Hedged by CTV and attributed to groups and doctors; no primary documentation cited. State only as 'CTV reported … appears to be'.
Source: CTV News, April 2022 (via Smoke-Free Housing BC; redacted copy), CTV News (news article) Link to this fact
Laws and loopholes / Other evidence
CTV quoted a health-law professor (Trudo Lemmens) calling it "a concerning case" that highlights concerns about expanding medically assisted death, and a MAiD-providing ICU physician (Dr. Scott Anderson) saying Track Two cases are complex and that patients with chronic conditions who cannot get services sometimes ask for assisted death.
Weak evidence: Two experts' opinions as quoted by one outlet; Anderson speaks generally, not about her case. Death by MAiD is the subject; add 988 line in published use.
Source: CTV News, April 2022 (via Smoke-Free Housing BC; redacted copy), CTV News (news article) Link to this fact
Laws and loopholes / Other evidence
CTV reported that she wrote to officials at all levels of government, and that the signing physicians' and her own letters, per the ASEQ-EHAQ president, drew no responses.
Weak evidence: Advocate's account; no officials quoted; CTV does not say it asked them. Death by MAiD is the subject; add 988 line in published use.
Source: CTV News, April 2022 (via Smoke-Free Housing BC; redacted copy), CTV News (news article) Link to this fact
Laws and loopholes / Other evidence
Inclusion Canada says a woman with multiple chemical sensitivities was forced to live in one room from October 7, 2019, after the Ontario Human Rights Tribunal did not provide safe air quality in her apartment.
Weak evidence.
Caveats
Advocacy post by an organization, written a year later; not independent reporting. Attribute to Inclusion Canada. The post gives no Tribunal file number, date or order; the Tribunal context rests on one sentence.
Source: Inclusion Canada: Remembering Sophia (advocacy post, Feb 22, 2023; redacted copy), Inclusion Canada blog post Link to this fact
Laws and loopholes / Other evidence
In a letter dated October 20, 2021, as quoted by Inclusion Canada, her doctors wrote that a patient had applied for and been found eligible for medical assistance in dying, and urged the government: "We urge you to do something and communicate with us as quickly as possible."
Weak evidence.
Caveats
Advocacy post by an organization, written a year later; not independent reporting. Attribute to Inclusion Canada. The letter is quoted by the organization; the original letter is not in our evidence base. Patient identifiers are removed in the redacted copy.
Source: Inclusion Canada: Remembering Sophia (advocacy post, Feb 22, 2023; redacted copy), Inclusion Canada blog post Link to this fact
Laws and loopholes / Other evidence
Inclusion Canada describes Bill C-7 (law since March 17, 2021) as making medical assistance in dying legal for disabled people whose deaths are not reasonably foreseeable, and says the law puts people in her situation at risk.
Weak evidence.
Caveats
Advocacy post by an organization, written a year later; not independent reporting. Attribute to Inclusion Canada. The date matches the statute page; the risk claim is the organization's opinion.
Source: Inclusion Canada: Remembering Sophia (advocacy post, Feb 22, 2023; redacted copy), Inclusion Canada blog post Link to this fact
Laws and loopholes / Government agency
The CHRC says scent-free policies should apply to employees and non-employees alike, name the products to avoid, be flexible, and carry consequences for non-compliance, and that employers should stay open to other accommodation options.
Weak evidence: Policy-design advice with no cited evidence base (footnotes not captured).
Source: CHRC 2026 web Link to this fact
Laws and loopholes / Other evidence
Disability ethicist Heidi Janz says that Sophia, a Toronto woman with MCS who died by MAiD in 2022, asked her to keep telling her story "in the hopes that other people wouldn't have to make the decision that she did."
Weak evidence: Single interview testimony relayed through a support person; the transcript is reconstructed from page HTML; no documents.
Source: Chemical Sensitivity Podcast ep. 101, 2026 Link to this fact
Laws and loopholes / Other evidence
A friend of Sophia says an attempt to seal Sophia's building made conditions worse because the person doing the work "really wasn't qualified to understand the way the air movement was working in the building," and that Sophia chose MAiD afterward.
Weak evidence.
Caveats
One friend's recollection; contractor, building and dates unidentified; not corroborated by any record on this page; speaker's account is not a finding about why Sophia sought MAiD.
Source: Chemical Sensitivity Podcast ep. 101, 2026 Link to this fact
Laws and loopholes / Other evidence
Janz says she believes Sophia had spent two years writing to local, provincial and federal officials about her housing situation, with doctors also advocating, without result.
Weak evidence: Testimony only; the same episode gives her age as 51 (host) and 53 (Janz), so details recalled by speakers are not independently confirmed.
Source: Chemical Sensitivity Podcast ep. 101, 2026 Link to this fact
Laws and loopholes / Other evidence
Janz argues that the choice of MAiD cannot be considered free for disabled people until they have free choice in where, with whom and how they live, and that without safe, affordable housing and supports MAiD "amounts to a eugenics program."
Weak evidence: Stated opinion of one disability-rights activist; she says it is strong language; this page records the position, it does not assess it.
Source: Chemical Sensitivity Podcast ep. 101, 2026 Link to this fact
Laws and loopholes / Other evidence
Janz says that under the UN Convention on the Rights of Persons with Disabilities governments must ensure access to safe housing and safe environments for people with MCS, and that Canada, though a signatory, tends to ignore those commitments.
Weak evidence: Opinion on treaty compliance; no legal analysis in the episode.
Source: Chemical Sensitivity Podcast ep. 101, 2026 Link to this fact
Laws and loopholes / Other evidence
Janz says clinicians who cannot or will not distinguish illness from chemical exposure in housing are being discriminatory and have an ethical duty to work harder to diagnose those factors.
Weak evidence: Ethicist's opinion; no clinical evidence presented.
Source: Chemical Sensitivity Podcast ep. 101, 2026 Link to this fact
Laws and loopholes / Other evidence
Station wastewater treatment in Antarctica (biological treatment with UV or chlorine) is judged by the authors to be ineffective for personal-care chemicals, and one-third of permanent and two-thirds of summer stations have no treatment.
Weak evidence: Efficacy is asserted, not quantified for these compounds; the authors admit plant conditions differ too much to compare treatments.
Source: Balakrishna 2023 (review), Environmental Research Link to this fact
Skin allergy / Measured in people or real products
Most patients who reacted to oxidized scent chemicals (58%) also had other fragrance allergies or a history of reacting to fragranced products.
Weak evidence: 31 positive patients.
Skin allergy / Measured in people or real products
People without skin disease reacted to oxidized limonene and linalool as strongly as dermatitis patients.
Weak evidence: Small groups (9 controls per comparison after exclusions).
Source: Bråred Christensson 2009, Contact Dermatitis Industry-funded Link to this fact
Skin allergy / Lab study (cells or chemistry)
In lab tests on human skin cells, the oxidized forms of limonene and linalool reshaped the cells' fats in the same way as a classic potent skin allergen (DNFB), a pattern consistent with oxidative stress.
Weak evidence: One cell line, one dose.
Skin allergy / Lab study (cells or chemistry)
In lab tests on reconstructed human skin, oxidized linalool broke down into reactive radicals that bind to skin proteins, which helps explain why linalool becomes an allergen only after it reacts with air.
Weak evidence: Skin model and model thiols; mechanism, not prevalence.
Source: Kuresepi 2020, Chemical Research in Toxicology Link to this fact
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 / Measured in people or real products
Once someone is sensitized, patch tests can trigger reactions at low ppm concentrations of oxidized terpene, but the specific 'as low as 1 ppm' figure is for Δ³-carene in older, narratively-reviewed occupational turpentine literature; for the two terpenes that dominate consumer exposure, modern peer-reviewed dose-response studies put the threshold one to two orders of magnitude higher (limonene hydroperoxides: ~24 ppm single patch application, ~140 ppm repeated realistic exposure, ED₁₀ ≈85 ppm; linalool hydroperoxides: ~560 ppm repeated realistic exposure).
Weak evidence.
Caveats
The 1 ppm figure applies to Δ³-carene in historical occupational patch testing, not to limonene or linalool, and its own study design (occlusion, participant numbers) is not given in the citing review. No limonene- or linalool-specific study supports reactions at ~1 ppm.
Source: Karlberg & Lepoittevin 2021, Contact Dermatitis Link to this fact
Skin allergy / Measured in people or real products
All four patients already allergic to oxidized linalool reacted to air-exposed lavender oil on patch testing.
Weak evidence: N=4 pre-selected sensitized patients; fresh oil not tested alongside; elicitation, not sensitization.
Source: Hagvall 2008, Contact Dermatitis Industry-funded Link to this fact
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
By 2007, Fragrance Mix II, a newer fragrance patch-test screen, was showing a high and still-rising rate of positive reactions in German clinic data, on top of the original Fragrance Mix I.
Weak evidence.
Caveats
Cites the original FM II validation studies (Frosch et al. 2005) plus an unpublished personal communication (IVDK network) for the 'still increasing in 2007' claim; neither is independently verified here.
Source: Brasch 2007, Current Opinion in Allergy and Clinical Immunology Link to this fact
Skin allergy / Review of other studies
People sensitized to hydrolyzed wheat protein in cosmetics do not necessarily react to intact wheat protein, so they can generally still eat wheat/bread without a reaction.
Weak evidence: Stated in passing in a narrative review, citing a single 2006 study; not itself verified against the primary.
Source: Brasch 2007, Current Opinion in Allergy and Clinical Immunology Link to this fact
Skin allergy / Review of other studies
In one clinic-based dose study, the paraphenylenediamine concentration that elicited at least a weak positive patch-test reaction in 10% of already PPD-sensitized people was 38 ppm, well below the concentrations permitted for hair dyes — raising the question of whether the standard 1% patch-test concentration is itself safe to apply.
Weak evidence: Threshold applies to already-sensitized individuals in one cited dose-response study, not to the general population's exposure risk; relayed secondhand.
Source: Brasch 2007, Current Opinion in Allergy and Clinical Immunology Link to this fact
Skin allergy / Review of other studies
Fragrance is the most common cause of allergic contact dermatitis in the armpit, and deodorants and antiperspirants are a major source of that fragrance exposure.
Weak evidence: Narrative clinical review with no new data of its own; relays a 1982 cosmetic-product survey and later studies not independently re-checked here.
Source: Musicante 2024, Cutis Industry-funded 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
Fragrance causes both irritant and allergic contact dermatitis, among other adverse skin reactions, and fragrances are the most frequent chemicals causing contact dermatitis overall.
Weak evidence.
Caveats
Narrative review statement, not a ranked prevalence study; does not establish that contact dermatitis (from any cause) is the single most common adverse reaction to skincare products in general, only that fragrance is a leading cause of contact dermatitis specifically and that it can be either irritant or allergic.
Source: Pastor-Nieto 2021, Current Treatment Options in Allergy Link to this fact
Skin allergy / Review of other studies
Fragrance chemicals are also used as food flavorings, and dermatologists consider systemic contact dermatitis from fragrance-related food flavorings in fragrance-allergic patients whose eczema does not clear after 6 weeks of full topical fragrance avoidance.
Weak evidence: Clinical management guidance from a narrative review, not a measured ingestion-exposure or prevalence study; does not quantify how often food flavorings are the actual culprit.
Skin allergy / Review of other studies
Certain fragrance and botanical ingredients have been linked to pigmented cosmetic dermatitis (facial hyperpigmentation), reported mainly in Japan in the 1960s-1970s; the condition became rare after 1978 reformulation of the implicated products.
Weak evidence.
Caveats
Relayed from a narrative review's historical summary (citing older Japanese case-report literature, e.g. Nakayama); no prevalence data or systematic count of cases is given, and a companion evidence base source page (src-2020-review-perfume-present-status-associated-allergens) names specific implicated ingredients (ylang-ylang, jasmine absolute, cananga, benzyl salicylate, hydroxycitronellal, sandalwood, geraniol) but the video's decade range (1970s-80s) is only approximately matched (source says 1960s-1970s).
Source: de Groot 2020, Dermatitis 31(1):13-35, Dermatitis® Link to this fact
Skin allergy / Other evidence
The National Eczema Association's Seal of Acceptance certification criteria exclude chemical UV-absorber sunscreens, accepting only physical (mineral) sunscreens containing titanium, zinc, or iron oxide.
Weak evidence.
Caveats
This reflects one certification body's precautionary ingredient-exclusion criteria for eczema-prone skin, not measured comparative allergic-contact-dermatitis incidence rates between mineral and chemical UV filters — no such comparative rate data were found in our evidence base or in this pass. Do not read this as evidence that mineral filters cause fewer ACD reactions in the general population, only that this eczema-focused body's rules treat them as the safer default.
Source: National Eczema Association 2026 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
Hairdressers who wore gloves during dye application did not have significantly lower hand loads of hair-dye chemicals than those who did not, but the gloves were often re-used for months, put on after mixing, or turned inside out, and glove users did the more hand-intensive whole-head jobs.
Weak evidence: Glove use was confounded with task and technique; 3 vs 1 hairdressers had PPD; not a test of properly used single-use gloves.
Source: Lind et al. 2005, The Annals of Occupational Hygiene Link to this fact
Skin allergy / Other evidence
Oxidative hair dyes are made by mixing PPD or toluene-2,5-diamine and coupler creams with a hydrogen peroxide cream, and these reactive compounds were still found unreacted on hairdressers' hands, with the authors noting that hydrogen peroxide contact enhances their oxidation.
Weak evidence: The study measured parent amines only, not oxidation products such as Bandrowski's base; the oxidation statement is the authors' general comment.
Source: Lind et al. 2005, The Annals of Occupational Hygiene 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
Four of 21 contact-allergic patients (19%) reported delayed skin symptoms the authors judged compatible with a type-IV (delayed allergic) reaction after inhaling their allergen.
Weak evidence: The 'four' includes one patient whose eczema was already present and did not worsen and one with itch only; only two had objective flares.
Source: Schnuch 2010, 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
Only 6 of 25 Spanish patients (24%) allergic to both imidazolidinyl urea and diazolidinyl urea also reacted to formaldehyde, suggesting a shared non-formaldehyde allergen in these two preservatives.
Weak evidence: Small subgroup in one retrospective series; the 'compound HU' explanation is the authors' hypothesis from other work and was not tested here.
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 / Measured in people or real products
Clinicians rated 96-100% of the commonest textile-dye and resin positives as relevant to the patient's exposure, but this was a same-visit judgment, not confirmed by garment testing.
Weak evidence: Relevance judged by nurse or physician at reading, subjective, no follow-up or garment analysis; the authors list this as a limitation.
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
Clothing dermatitis in this series sat where garments press tightly on skin (chest 26%, thighs 23%, abdomen 21%, legs 21%, armpit folds 15%), and synthetic fabrics (39.4%) and dyes (46.3%) were the most-blamed causes by history; silk was always tolerated.
Weak evidence: Patient-reported suspicion at history, not tested fiber by fiber; single multicenter Italian case series, no exposure measurement.
Skin allergy / Other evidence
Formaldehyde and its finishing resins were uncommon allergens in this Italian series of allergic textile dermatitis (5.8% and 5.2%) compared with much higher resin positivity reported in Israel and Rochester (about 20-25% to melamine formaldehyde resin), which the authors attribute to resins that release less formaldehyde.
Weak evidence.
Caveats
The attribution to low-release resins is the authors' inference with no garment measurement; cohorts differ (confirmed versus suspected textile dermatitis); this is not a measure of formaldehyde in clothing.
Skin allergy / Other evidence
Health care workers appear more often sensitized to BAK: one cited study found 7.5% relevant BAK reactions in health care workers versus 2.3% in other patients, and another 23.8% of 223 nurses sensitized.
Weak evidence: Relayed from other studies of small, selected groups; a third cited study found only a slight excess (2.0% vs 1.6% control).
Skin allergy / Other evidence
Related cationic ingredients such as behentrimonium methosulfate, cetrimonium chloride, and benzethonium chloride are suspected cross-reactors with BAK, and one patient's dermatitis improved only after a conditioning-moisturizer ingredient was stopped.
Weak evidence.
Caveats
Two cases, no patch testing of the cross-reactors, and no controlled evidence of cross-reactivity; the avoidance database the authors used did not list all of them. The industry-funded CIR 2010 trimonium draft has no toxicology data for behentrimonium methosulfate and reports no human sensitization to cetrimonium chloride (0.25%) or behentrimonium chloride (2.4% active), but it never tests benzalkonium cross-reactivity, so it neither confirms nor excludes the suspicion.
Skin allergy / Other evidence
Benzalkonium chloride, the most common eye-drop preservative, was positive in 10 eye-medication patients (1.1% of the 885 tested), rising to 2% of those tested in 1999-2007 and falling to 0.3% in 2008-2016.
Weak evidence: Small counts (1, 8, 1 positives per period) in selectively tested patients; the authors note BAK is also an irritant and counted only reactions that looked allergic.
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
Acetophenone azine, a chemical found in foam (EVA) shin guards, shoe insoles, and flip-flops, has caused allergic skin reactions in a small number of young athletes in Europe and Canada.
Weak evidence: Roughly a dozen documented patients, all from case literature; no prevalence data; the column is a society award announcement.
Information, not medical advice. See also: myths we won’t tell you.