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Patch Test

Also known as: patch testing, skin test, sensitivity test, allergy alert test

Two different procedures sharing a name: diagnostic patch testing, a dermatology investigation applying standardised allergen concentrations under occlusion and reading them at fixed intervals to identify type IV delayed hypersensitivity; and the salon pre-service skin test, an unoccluded application of a working product read once by a lay person.

Evidence status

Contested

Diagnostic patch testing has guideline and registry support: the 2026 ESCD Delphi-consensus update specifies controlled allergens, occlusion and timed readings. Salon and consumer pre-service testing rests only on manufacturer-involved elicitation studies in people already known to be PPD-allergic; the leading independent critique says it is unvalidated and was tested in the wrong population. No study shows that pre-service testing reduces allergic-reaction incidence or supports patch testing before chemical peels or microneedling.

What patch testing is, and the types available#

Two different procedures share the name.

Diagnostic patch testing is a specialist dermatology investigation for type IV delayed hypersensitivity. Standardised allergen concentrations in defined vehicles are applied under occlusion, usually for 48 hours, and assessed over several appointments against recognised grading criteria. A baseline series contains around 50 substances.[1, 2, 3]

Pre-service skin testing, also called an allergy alert test by some manufacturers, applies a working product before a salon or consumer service. It is generally unoccluded and is performed according to the product’s instructions. It is not a simplified version of the hospital investigation: the material, concentration, setting, reader and purpose are different.[5, 6]

In diagnostic testing, p-phenylenediamine (PPD) is used at a controlled 1% concentration in petrolatum rather than at the working concentration used in a colour service. Readings are taken at least at patch removal around day 2 and again around day 4; later reactions may still develop. These details describe the medical investigation and do not create a salon protocol.[2, 3][3, 4, 10]

Use of patch testing in aesthetic practice#

A pre-service test sits within product selection, client history and the instructions for the exact product. Those instructions determine application site, quantity, mixing, rinsing and reading time because methods differ between manufacturers and even between products from the same company. In a survey of 40 oxidative hair dyes from 21 manufacturers, 39 instructed self-testing and the methods varied across every one of those features.[5, 6]

In Great Britain, PPD in oxidative hair dye is limited to 2% free base after mixing. The label must carry specified warnings, including that severe allergic reactions can occur, that the product is not intended for people under 16, that black henna can increase risk, and that hair colourants must not be used on eyelashes or eyebrows.[4]

A product specifically intended for colouring eyelashes may contain PPD up to 2% free base after mixing in Great Britain, but it must be labelled for professional use only. That is a different product category from hair colourant applied near the eye.[4, 13]

The GB Cosmetics Regulation does not require a 48-hour allergy test. Its Annex III sets concentration limits and warning wording but contains no statutory testing duty. The testing requirement comes from the specific manufacturer’s instructions and may also arise contractually; no retrievable insurer or trade-body policy wording was located that establishes a universal UK insurance requirement.[4]

England’s green/amber/red aesthetics tiers are still a 2023 consultation proposal. The proposal placed superficial peels and microneedling in green and said nothing about pre-service allergy testing; the 2025 response deferred procedure classification, and no scheme is in force.[14]

Contraindications and cautions#

A pre-service test does not override a product warning. Where the label says not to colour because of age, a previous hair-colour reaction or a black-henna history, applying a small amount to “check” is not an alternative route to the service.[4]

Active dermatitis, broken or infected skin at the proposed site, a previous immediate reaction, or symptoms suggesting an established contact allergy require a different decision from routine screening. A person with a genuine history of reactions needs medical assessment rather than repeated exposure to a working salon product.

The type of reaction matters. Patch testing is designed for delayed, cell-mediated type IV hypersensitivity. It does not test for an immediate type I reaction and cannot exclude anaphylaxis.[1, 2]i

Diagnostic patch testing also carries its own specialist cautions and interpretation limits. It belongs in a dermatology service; a salon application should never be described as a diagnosis of allergy.

Clinical uses and the evidence behind them#

Allergic contact dermatitis

Diagnostic patch testing is the reference investigation for suspected allergic contact dermatitis. Standardised allergens, occlusion, multiple readings and clinical interpretation allow the reaction to be linked to relevant exposures.[1, 2, 3]

Among people referred to European dermatology clinics for suspected hair-product allergy, age-standardised PPD sensitisation was 19.7% in female hairdressers and 31.6% in female consumers. These are clinic populations, not prevalence estimates for the general public.[9]

Within patch-tested populations, hair dyeing was associated with sixfold greater odds of PPD sensitisation (OR 6.0, 95% CI 3.9–9.4), black henna with 2.4-fold greater odds (95% CI 1.5–3.7) and working as a hairdresser with 2.1-fold greater odds (95% CI 1.3–3.2).[10]

Pre-service product testing

The strongest supportive clinical study tested people already diagnosed as PPD-allergic. A visible reaction occurred in 38 of 42 on the forearm and 39 of 42 behind the ear; all 48 non-allergic controls were negative. Four authors worked for Kao, Henkel, Coty or L’Oréal, and the L’Oréal author was the corresponding author. This is elicitation in known allergic participants, not a measure of how well an unselected client’s negative result predicts a safe service.[7]

An independent review concluded that the consumer self-test had not been validated as a screening test and had been evaluated in the wrong population. No published sensitivity, specificity, positive predictive value or negative predictive value was located for the real-world unoccluded test read by a lay person. No study was located showing that it reduces the incidence of allergic reactions; a systematic review judged its efficacy doubtful because the conditions are not standardised.[5][8]i

No indexed evidence was located for pre-treatment patch testing before chemical peels or microneedling. Where a manufacturer requires testing, that instruction still governs; the evidence absence means the practice cannot be presented as a clinically validated universal safety screen.[no source found]

Selecting a pre-service test#

The selection is product-specific. The exact colour, tint, peel or other formulation intended for the service determines whether testing is required and which manufacturer instruction applies. A test for one formulation does not establish tolerance to another.

The product name, batch, preparation, application site and result are meaningful only when recorded with the timing and the identity of the person who read it. The record describes what happened; it does not convert a negative result into an assurance that no reaction can occur.

A manufacturer’s instruction takes precedence over a method copied from a general training manual. Where the instruction is absent, unclear or conflicts with contractual insurer requirements, clarification belongs with the manufacturer and insurer rather than with an invented generic protocol.

Adverse effects and their management#

Local delayed reactions

A positive pre-service reaction may present as erythema, itching, swelling or dermatitis at the application site. A published lash-dye case described severe eyelid and periorbital dermatitis with conjunctivitis after beautician-applied permanent lash dye; diagnostic tests were positive to PPD at 0.01% and 1% and to the dye itself.[13]

Sensitisation from testing

Leaving a strong sensitiser on skin at working concentration creates a plausible risk of active sensitisation. The dataset designed to investigate this contained too few pretested patients to analyse, so the risk remains unmeasured rather than excluded.[5, 10]

Immediate systemic reactions

A delayed-type test cannot exclude anaphylaxis. A UK inquest recorded the death of a 39-year-old from anaphylactic shock after hair dye; her hair-dye allergy had been documented since 2005. The coroner also recorded evidence that 86% of users knew a 48-hour test was advised while only 5% performed one. Those figures are inquest evidence, not population epidemiology.[11][11]

Anaphylaxis can occur without skin signs in up to 20% of cases. Suspected anaphylaxis follows current Resuscitation Council UK emergency guidance, the clinic’s emergency plan and the 999 pathway; where the person carries a prescribed adrenaline auto-injector, its own instructions govern use. This does not expand a non-healthcare practitioner’s authority to supply or administer a medicine.[12]

Referral and scope boundaries#

Diagnostic patch testing belongs to dermatology. Referral is indicated where there is a previous reaction to hair colour, lash tint or black henna; recurrent or unexplained dermatitis; an immediate reaction; extensive facial or eyelid swelling; breathing, circulation or systemic symptoms; or uncertainty about whether a presentation is allergic, irritant or another diagnosis.

A salon test does not identify the responsible allergen, assess cross-reactivity or establish that a later service is safe. It should be documented as a manufacturer allergy-alert or pre-service skin test rather than represented as hospital-equivalent patch testing.

Any suspected anaphylaxis is an emergency. Emergency response follows the clinic’s plan and Resuscitation Council UK guidance; ongoing allergy investigation follows through an appropriately qualified medical service.[12]

Mechanism of action#

Allergic contact dermatitis is a type IV delayed, T-cell-mediated hypersensitivity. Diagnostic patch testing recreates a small, controlled exposure under occlusion so that a sensitised immune response can be read over time.[1, 2, 3]

Immediate urticaria or anaphylaxis follows a different pathway. Because a delayed test and an immediate reaction measure different immune processes, a negative delayed response cannot rule out an immediate systemic event.[1, 2]

Commonly misstated claims#

“The 48-hour patch test is a legal requirement.”

GB law sets PPD concentration limits and mandatory warnings, but Annex III contains no requirement for an allergy, skin, self- or patch test.[4]

Supported statement: the exact manufacturer’s instructions and any contractual insurer term govern pre-service testing; it is not a general statutory 48-hour duty.

“A negative patch test means the client is safe.”

The salon-style test has no published real-world sensitivity, specificity or predictive values. The strongest positive study asked whether known PPD-allergic people could be made to react, not whether an unselected client with a negative result would tolerate a service.[5, 7][no source found]

Supported statement: a negative result records no visible delayed reaction under those test conditions; it does not guarantee a reaction-free service.

“Patch testing rules out anaphylaxis.”

Patch testing investigates delayed type IV hypersensitivity. Anaphylaxis is an immediate systemic reaction and is not excluded by it.[1, 2, 11]

Supported statement: a delayed test and an immediate reaction assess different immune pathways, so emergency readiness remains necessary.

“Patch testing before a peel is evidence-based best practice.”

No indexed study of pre-treatment testing before chemical peels or microneedling was located.

Supported statement: where the product manufacturer requires a pre-service test, that instruction governs; a universal preventive benefit has not been demonstrated.

Areas of remaining uncertainty#

  • Whether repeated pre-service testing can itself induce sensitisation has not been quantified; unnecessary exposure to a strong sensitiser should therefore not be presented as risk-free.[5, 10]
  • No comparative evidence establishes whether 24, 48 or 72 hours is the best reading interval; the manufacturer’s instruction for the exact product remains the operative timing.
  • No source was located for the common six-month retesting convention; repeat requirements therefore come from the product or insurer rather than a universal evidence-based interval.
  • Cross-reactivity means a negative result to one formulation may not travel to another; product-specific documentation remains necessary.
  • UK population incidence of hair- and lash-colour reactions is not established; clinic referral figures and inquest evidence should not be converted into population risk.[9, 11]
  • No retrievable insurer wording established a universal UK testing condition; actual policy documents must be checked before insurance requirements are stated.[no source found]

Frequently asked questions#

Is a salon allergy alert test the same as a hospital patch test?

No. Diagnostic testing uses standardised allergens, occlusion, several readings and specialist interpretation. A salon test applies one working product under that manufacturer’s instructions.[1, 2, 3, 5, 6]

Does a negative result clear the client for treatment?

No. It records the result under those conditions and cannot exclude a later delayed reaction or an immediate systemic reaction.

Is pre-service testing legally required in Great Britain?

Not by Annex III of the Cosmetics Regulation. Manufacturer instructions and contractual requirements may still require it.[4]

Can one brand’s test cover another brand?

That is not established. Instructions and formulations vary, including between products from one manufacturer, so the product intended for use supplies the governing instruction.[5, 6]

Should a patch test be performed before every peel or microneedling treatment?

There is no evidence-based generic rule. The instructions for the exact product govern, and a medical diagnostic patch test is a different procedure.

References#

Each source is graded by evidence tier. Tier 4 material (manufacturer documents, expert consensus, practitioner experience) is useful for protocol and context, and is never presented as equivalent to independent clinical evidence.

  1. Uter W, Aerts O, Agner T, Brans R, Bruze M, Cannavó A, et al. European Society of Contact Dermatitis Guideline for Diagnostic Patch Testing — Recommendations on Best Practice (Update 2026). Contact Dermatitis. Published online 21 June 2026. doi:10.1111/cod.70195. PMID 42324086.Tier 1Supports: Twenty-four-author European guideline (author list verified against the PubMed record: Uter, Aerts, Agner, Brans, Bruze, Cannavó, Crépy, Giménez-Arnau, Gonçalo, Goossens, John, Lidén, Hadžavdić, Mahler, Matura, Özkaya, Pesonen, Raison-Peyron, Rustemeyer, Spiewak, Stingeni, White, Wilkinson, Johansen) updating Johansen JD, Aalto-Korte K, Agner T, et al., Contact Dermatitis 2015;73(4):195-221, doi:10.1111/cod.12432, PMID 26179009 — 2015 citation verified against PubMed. Abstract states the guideline 'summarizes all aspects of patch testing for the diagnosis of contact allergy in patients suspected of suffering, or having been suffering, from allergic contact dermatitis or other delayed-type hypersensitivity skin and mucosal conditions', with practical recommendations 'consensualized in a Delphi process'. Named sections cover materials, technique, modifications of epicutaneous testing, individual factors influencing outcome, children, occupational contact dermatitis and drug eruptions, patch testing of patient-brought materials, adverse effects of patch testing, and final evaluation and patient counselling. SCOPE LIMIT: this establishes that diagnostic patch testing is a specialist medical procedure defined by delayed-type hypersensitivity and governed by consensus guidance — it says nothing about salon pre-service testing. Full text was paywalled (HTTP 402) so the exact reading-day and concentration wording could not be quoted verbatim from this source; those specifics are carried by sources 2 and 3.
  2. British Association of Dermatologists. Patch testing — patient information leaflet. Skin Health Information (BAD), accessed 1 August 2026.Tier 4Supports: UK professional-body patient information. Verbatim: patch testing is 'a specialist procedure carried out in dermatology departments'; 'Patch tests will not detect food allergies'; the baseline panel is 'the most common 50 or so' substances including 'metals, perfumes, rubber chemicals, preservatives, cosmetics and plants'; patients 'attend the hospital: typically for 3 appointments during a one-week period'; 'The substances will remain taped in place for 48 hours, or until your second visit'; 'Any reactions are noted at the second visit'; on the third visit the back 'will be checked (examined)'; 'A reaction can occasionally occur after the 3rd appointment. If you do develop a late reaction, please take photographs and contact your clinic.' Listed reasons a doctor may decide not to patch test: pregnancy or breastfeeding, extensive eczema on the back, sunbed/sunbathing in the previous 6 weeks, moderate or high dose oral steroids, topical steroids to the back within 72 hours, other immunosuppressive drugs. All of the above re-verified verbatim against the live BAD page on 1 August 2026. SCOPE LIMIT: patient-facing leaflet, a patient-facing leaflet, not a graded clinical guideline. It is typed 'expert-consensus' tier 4 to match the corpus-wide convention for BAD patient information leaflets, but it must never be presented as a UK clinical guideline; confirmed by direct check that it does NOT mention 96 hours or day 4 anywhere, so it cannot carry the second-reading interval — that is carried by source 3 alone.
  3. Bacharewicz-Szczerbicka J, Reduta T, Pawłoś A, Flisiak I. Paraphenylenediamine and related chemicals as allergens responsible for allergic contact dermatitis. Arch Med Sci. 2021;17(3):714-723. doi:10.5114/aoms.2019.86709. PMID 34025842, PMC8130485. CITATION NOTE: PubMed and PMC index the year as 2019 (online-ahead-of-issue); volume 17 issue 3 of Archives of Medical Sciences carries a 2021 cover date. Both years refer to the same paper; 2021 is used here for the volume-matched citation.Tier 3Supports: Retrospective chart review, single Polish dermatology department, 4,087 patients patch-tested for allergic contact dermatitis 2007-2015. Method verbatim: 'The patch test results were read twice, 30 min after antigen removal (day 2) and 48 h after the first reading (day 4), and categorized according to the International Contact Dermatitis Research Group criteria.' Concentrations used: PPD 1.0% pet, IPPD 0.1% pet, ethylenediamine 1.0% pet, triethylenetetramine 0.5% pet, toluene-2,5-diamine 1.0% pet. Results: 166/4,087 (4.1%) positive to PPD or a related amine; of these, 77.1% to PPD, 20.5% to IPPD, 6% to TDA, 1.2% to TETA, 0.6% to EDA; occupational character established in 34.3%; personal atopy in 36.7%; 98% presented as ACD, most often on the hands; patients with extremely strong PPD reactions more frequently cross-reacted to other para-group chemicals, especially benzocaine. Paper also states European ACD-clinic PPD prevalence is 'estimated to be 1.5-6%'. SCOPE LIMIT: single-centre, clinic-referred population — not general-population prevalence.
  4. Assimilated Regulation (EC) No 1223/2009 on cosmetic products, Annex III (restricted substances), entries 8a and 8b. legislation.gov.uk, as it applies in Great Britain, accessed 1 August 2026.Tier 1Supports: Entry 8a, p-Phenylenediamine and its salts, product type 'Hair dye substance in oxidative hair dye products', general use (a) and professional use (b): 'After mixing under oxidative conditions the maximum concentration applied to hair must not exceed 2 % calculated as free base.' Mandatory label wording for (a) includes: 'The mixing ratio. Read and follow instructions. This product is not intended for use on persons under the age of 16. Temporary “black henna” tattoos may increase your risk of allergy. Do not colour your hair if: you have a rash on your face or sensitive, irritated and damaged scalp, you have ever experienced any reaction after colouring your hair, you have experienced a reaction to a temporary “black henna” tattoo in the past. Contains phenylenediamines. Do not use to dye eyelashes or eyebrows.' plus 'Hair colourants can cause severe allergic reactions.' Professional wording (b) adds 'For professional use only.' and 'Wear suitable gloves.' Entry 8b, same substances, product type 'Products intended for colouring eyelashes': 'After mixing under oxidative conditions the maximum concentration applied to eyelashes must not exceed 2 % calculated as free base'; 'For professional use only.'; label must state 'This product can cause severe allergic reactions... This product is not intended for use on persons under the age of 16... Eyelashes shall not be coloured if the consumer: has a rash on the face or sensitive, irritated and damaged scalp, has experienced any reaction after colouring hair or eyelashes, has experienced a reaction to a temporary “black henna” tattoo in the past. Rinse eyes immediately if product comes into contact with them. Contains phenylenediamines. Wear suitable gloves.' Entry 8 (N-substituted derivatives of p-phenylenediamine) permits 3% free base on hair with equivalent warnings. NEGATIVE FINDING, verified by full-text search of the fetched Annex III: the phrases '48 hour', '48 h', 'allergy test', 'skin test', 'sensitivity test', 'preliminary test', 'self-test' and 'patch test' return zero occurrences — Annex III mandates warning wording and concentration limits but imposes no requirement to perform any pre-use allergy test.
  5. Thyssen JP, Søsted H, Uter W, Schnuch A, Giménez-Arnau AM, Vigan M, Rustemeyer T, Granum B, McFadden J, White JM, White IR, Goossens A, Menné T, Lidén C, Johansen JD. Self-testing for contact sensitization to hair dyes — scientific considerations and clinical concerns of an industry-led screening programme. Contact Dermatitis. 2012;66(6):300-11. doi:10.1111/j.1600-0536.2012.02078.x. PMID 22568836.Tier 4Supports: Critical review by fifteen European contact dermatitis academics (National Allergy Research Centre Copenhagen, IVDK, Karolinska, St John's, KU Leuven and others). Concludes 'in its present form, the hair dye self-test has severe limitations', enumerated verbatim as: '(i) it is not a screening test but a diagnostic test; (ii) it has not been validated according to basic criteria defined by scientists; (iii) it has been evaluated in the wrong population group; (iv) skin reactions have been read by dermatologists and not by the targeted group (consumers and hairdressers); (v) hair dyes contain strong and extreme sensitizers that are left on the skin in high concentrations, potentially resulting in active sensitization; and (vi) recommendations and instructions on how to perform the hair dye self-test vary greatly even among products from the same company, again suggesting that the basis for safe use of the test has not been determined'. Closing warning: 'If the use of a hair dye self-test to predict contact sensitization becomes widespread, there is severe risk that a tool has been marketed that may cause morbidity in European consumers.' SCOPE LIMIT: a reasoned critique, not new primary data; the active-sensitisation risk it raises is argued from first principles and has not been quantified.
  6. Friis UF, Goossens A, Giménez-Arnau AM, Lidén C, Giménez-Arnau E, White IR, Alfonso JH, Uter W, Johansen JD. Self-testing for contact allergy to hair dyes — a 5-year follow-up multicentre study. Contact Dermatitis. 2018;78(2):131-138. doi:10.1111/cod.12882. PMID 28961320.Tier 3Supports: Product survey. In March 2016, 40 oxidative hair dye products from 21 manufacturers were bought in retail stores across 8 European countries and their consumer instructions compared with a 2011 baseline. Findings: consumers were instructed to perform a self-test before dyeing for 39 of the 40 products; 'the procedures varied greatly regarding the method of application, the amount of hair dye applied, the location and size of the application area, the number of applications, whether or not rinsing was performed after application, the reading times, and how a positive reaction was defined.' Conclusion: 'There are major variations in the instructions, even in products from the same manufacturer. The previously raised concerns regarding safety and validity still remain.' All figures (40 products, 21 manufacturers, 8 countries, 39 of 40 instructing a self-test) re-verified verbatim against the PubMed abstract. SCOPE LIMIT: this is an audit of instruction leaflets, not of patients or of outcomes — no human subjects were tested, so 'observational' should be read as a cross-sectional survey of product leaflets rather than of patients (the schema has no product-survey type); it says nothing about whether anyone who follows the instructions is protected. PubMed publication type: Multicenter Study.
  7. Coenraads PJ, Aberer W, Cristaudo A, Diepgen T, Holden C, Koch L, Schuttelaar ML, Weisshaar E, Fuchs A, Schlotmann K, Goebel C, Blömeke B, Krasteva M. Allergy Alert Test for p-Phenylenediamine-Allergic Hair Dye Users. Dermatitis. 2018;29(5):250-257. doi:10.1097/DER.0000000000000405. PMID 30234613.Tier 3Supports: Controlled elicitation study simulating consumer use conditions: open application for 45 minutes after mixing with developer, applied to forearm and behind the ear, using experimental products at 0.05%, 0.25%, 0.75% and 2% PPD. Participants: 42 PPD-positive, previously patch-test-diagnosed hair-dye-allergic subjects and 48 PPD-negative controls. Results: a self-noticeable reaction occurred in 90.5% (38/42) on the forearm and 93% (39/42) behind the ear; all 48 controls were negative; in subjects with (+++) diagnostic patch test reactions, 19 of 19 were positive; response strength and number of responders rose with PPD concentration. Abstract verbatim: 'Reactions were self-evaluated by subjects and independently assessed by dermatologists.' Every figure in this record (42 PPD-positive, 48 controls, 45-minute open application, 0.05/0.25/0.75/2% PPD, forearm and behind the ear, 38/42, 39/42, 19 of 19 at (+++), dose-response) was re-verified word for word against the PubMed abstract and is accurate. SCOPE LIMITS, load-bearing: this measures ELICITATION in people already known to be PPD-allergic, not the screening performance of the test in unselected consumers — it yields no sensitivity, specificity or predictive value for real-world use; reading was dermatologist-verified rather than left to the consumer; and the study says nothing about the far larger group of unsensitised users at risk of becoming sensitised.Funding / interest: Commercially conflicted. Four of the thirteen authors were employed by hair dye or cosmetics manufacturers at the time, verified against the published affiliations: A. Fuchs (Kao Germany GmbH, European Research Center, Darmstadt), K. Schlotmann (Henkel AG & Co KGaA, Dusseldorf), C. Goebel (Toxicology Department, Coty, Darmstadt) and M. Krasteva (Research and Innovation, L'Oreal, Clichy). MATERIAL ADDITION ON VERIFICATION: M. Krasteva of L'Oreal is the CORRESPONDING author of record, not merely a contributing co-author - the commercial party whose product the test is meant to protect authored and corresponded the study. The explicit funding and conflict-of-interest statements still could not be retrieved (Dermatitis full text returned HTTP 402; the University of Groningen repository record for this paper carries no funding or COI field), so the disclosure here rests on author affiliations plus corresponding authorship rather than on a declared funding line. Treat as industry-authored and industry-corresponded. Note also that the paper's own Background asserts 'Regulations in many countries require consumer self-testing for hair dyes' - an industry-authored regulatory framing that is NOT true of Great Britain, where the verified full-text search of Annex III (source 4) returns zero occurrences of any pre-use test requirement.
  8. Tsimpidakis A, Katoulis A, Nicolaidou E, Rigopoulos D, Stratigos A, Gregoriou S. Hair Dyes Sensitization and Cross-Reactions: Challenges and Solutions: A Systematic Review of Hair Dye Allergens' Prevalence. Dermatitis. 2024;35(1):13-23. doi:10.1089/derm.2023.0019. PMID 37352419.Tier 2Supports: Systematic review of hair dye allergen prevalence and cross-reactivity. Key statements verbatim: 'the main problem remains with p-phenylenediamine and related aromatic amines'; 'If allergy is suspected, patch testing identifies the responsible hapten'; 'Cross-reactions detected in patch-tested populations indicate that one cannot safely use alternatives, although cross-reactivity is not always clinically relevant'; and on the salon/consumer test, 'An open application hair dye allergy self-test is recommended by manufacturers for early detection of allergy predisposition in consumers, although the lack of standardized conditions makes the efficacy of this process doubtful.' Also: 'Appropriate use of hand gloves, especially nitrile, is the most efficient prevention measure for professional hand eczema.' SCOPE LIMIT: the review synthesises prevalence data from patch-test clinic populations; its statement on self-test efficacy is a judgement, not a pooled effect estimate — no trial of self-test efficacy exists to pool. TIER CORRECTION ON VERIFICATION (tier 1 -> tier 2): PubMed does carry the MeSH publication type 'Systematic Review' and the title claims one, but the abstract reports NO search strategy, NO databases searched, NO inclusion or exclusion criteria, NO PRISMA statement and NO registration number. It reads as a narrative review wearing a systematic-review label. Every quoted sentence above was re-verified verbatim against the abstract and is accurate, but the source should not be carried at the same tier as a method-reporting systematic review.
  9. Uter W, Hallmann S, Gefeller O, Brans R, Symanzik C, Oppel E, Lang C, Kränke B, Treudler R, Geier J. Contact allergy to ingredients of hair cosmetics in female hairdressers and female consumers — an update based on IVDK data 2013-2020. Contact Dermatitis. 2023;89(3):161-170. doi:10.1111/cod.14363. PMID 37315639.Tier 3Supports: Analysis of the Information Network of Departments of Dermatology (IVDK) multicentre patch test registry, January 2013 to December 2020: 920 female hairdressers (median age 28, 84% hand dermatitis) versus 2,321 female consumers with no professional background (median age 49, 71.8% head/face dermatitis), all tested for suspected ACD to hair products. Age-standardised sensitisation prevalences — p-phenylenediamine 19.7% (hairdressers) vs 31.6% (consumers); toluene-2,5-diamine 20% vs 30.8%; ammonium persulphate 14.4% vs 2.3%; glyceryl thioglycolate 3.9% vs 1.2%; methylisothiazolinone 10.5% vs 3.1%. Authors' own caveat quoted: 'as indication for patch testing may differ, prevalences cannot directly be compared.' SCOPE LIMIT, load-bearing: these are prevalences among people referred to dermatology clinics with suspected hair-product allergy — they are NOT the prevalence of PPD allergy in the general or salon-client population, and must never be quoted as such.
  10. Schubert S, Lessmann H, Schnuch A, Uter W, Geier J; IVDK. Factors associated with p-phenylenediamine sensitization: data from the Information Network of Departments of Dermatology, 2008-2013. Contact Dermatitis. 2018;78(3):199-207. doi:10.1111/cod.12920. PMID 29322532.Tier 3Supports: Retrospective analysis of 4,314 patients tested with PPD 1% pet across the IVDK network, 2008-2013, with six added exposure questions. Of 271 PPD-positive patients, 80% had had their hair dyed and 57% of those subsequently developed scalp dermatitis; only 11% had had a henna tattoo. Odds ratios for PPD sensitisation, verbatim: 'Hair dyeing [odds ratio (OR) 6.0; 95% confidence interval (CI): 3.9-9.4], henna tattoos (OR 2.4; 95%CI: 1.5-3.7) and being a hairdresser (OR 2.1; 95%CI: 1.3-3.2) increased the risk of PPD sensitization.' CORRECTION ON VERIFICATION: these were described here as 'Adjusted odds ratios'; the abstract does not describe them as adjusted and the word has been removed. The paper also reports a null result that had been omitted: 'Neither dyeing of own hair nor application of a temporary henna tattoo seemed to affect PPD sensitization in hairdressers.' CRITICAL NEGATIVE, verbatim: 'The self-administrated pretest with hair dye was performed by only a few patients, precluding a more detailed analysis.' The study lists 'exposure to hair dye pretests' among the putative risk factors it set out to quantify and was unable to do so. SCOPE LIMIT: clinic-referred German-speaking population; ORs are for sensitisation among patch-tested patients, not absolute population risk.
  11. Fell G, Assistant Coroner for the Western Area of North Yorkshire. Regulation 28: Report to Prevent Future Deaths — Julie McCabe. Dated 4 April 2015; published by the Chief Coroner 12 December 2023 (ref 2023-0508). Sent to Rt Hon Dr Vince Cable MP, the Director General of the CPTA, and the Chief Coroner.Tier 1Supports: Statutory Regulation 28 report under Schedule 5 of the Coroners and Justice Act 2009. Inquest conclusion verbatim: 'Accidental death due to a rare but known potential adverse reaction to hair dye which caused irreversible brain damage due to anaphylactic shock on 30th October, 2011.' Cause of death: acute cardiorespiratory arrest; longstanding severe anoxic brain damage; anaphylactic shock. Circumstances: Julie McCabe, aged 39, had a longstanding hair dye allergy documented from at least 2005, probably had a black henna tattoo in 2007, used colourants for about ten years, attended her GP 16-20 times and hospital twice for adverse reactions, and 'would have a reaction every time she used hair colourant'. Coroner's background findings include: 'Hair colourant used in the EC cannot legally contain more that 2% PPD which at the scalp equals 1mg'; 'Anaphylaxis is a rare but documented reaction according to research within the industry'; the SCCS in 2012 said 'PPD in hair dye remains a considerable concern for consumer safety'. On testing, verbatim: 'The instructions provided with colourant advises a test 48 hours before using. Research indicates that only 5% carry out the test, even though 86% are aware of the necessity of the test.' On under-reporting, evidence from a 1,800-person Amersham hospital sample: 14% (270) of users reported an allergic reaction of some nature, 15% of those sought medical help, and 0.02% reported it to the manufacturer, against industry spontaneous-report rates of 0.3-4.3 per million. On black henna: Spanish research in the Canary Islands found PPD content 'between 15% and 64%' against a 2% permitted level. SCOPE LIMIT, load-bearing: the 14%, 5% and 86% figures are evidence heard at inquest, not peer-reviewed epidemiology, and the underlying studies are not cited in the report; they should be attributed to the coroner's findings, not presented as published prevalence. Coroner identity, report date, reference and addressees re-verified against the judiciary.uk record: Geoffrey Fell, Assistant Coroner for the Western Area of North Yorkshire; report dated 04/04/2015; reference 2023-0508; addressed to Rt Hon Dr Vince Cable MP, the Director General of the CPTA, and the Chief Coroner HH Judge Peter Thornton QC. All passages quoted above confirmed verbatim.
  12. Resuscitation Council UK. Emergency treatment of anaphylaxis: Guidelines for healthcare providers. May 2021.Tier 1Supports: UK national guideline replacing the 2008 edition. Quotes the World Allergy Organization definition: 'A serious systemic hypersensitivity reaction that is usually rapid in onset and may cause death. Severe anaphylaxis is characterized by potentially life-threatening compromise in airway, breathing and/or the circulation, and may occur without typical skin features or circulatory shock being present.' Guidance verbatim: skin and/or mucosal changes (flushing, urticaria, angioedema) 'may be absent in up to 20% of cases'; 'Adrenaline is the first-line treatment for anaphylaxis. Give intramuscular (IM) adrenaline early (in the anterolateral thigh) for Airway/Breathing/Circulation problems'; 'A single dose of IM adrenaline is well-tolerated and poses minimal risk to an individual having an allergic reaction. If in doubt, give IM adrenaline'; 'Repeat IM adrenaline after 5 minutes if Airway/Breathing/Circulation problems persist'; IV adrenaline 'must be used only in certain specialist settings'. IM dose using 1 mg/mL (1:1000): adult and child over 12 years, 500 micrograms (0.5 mL); 6-12 years, 300 micrograms; 6 months-6 years, 150 micrograms. SCOPE LIMIT: written for healthcare providers; it does not address who may lawfully hold or administer adrenaline in a salon.
  13. Teixeira M, de Wachter L, Ronsyn E, Goossens A. Contact allergy to para-phenylenediamine in a permanent eyelash dye. Contact Dermatitis. 2006;55(2):92-4. doi:10.1111/j.0105-1873.2006.00883.x. PMID 16930233.Tier 4Supports: Single detailed case report. A 30-year-old atopic woman with a history of intolerance to dark stockings developed 'a severe dermatitis on the eyelids and peri-orbital regions, as well as a conjunctivitis after having her eyelashes tinted by a beautician' with a permanent black eyelash and eyebrow dye. Diagnostic patch tests were positive to PPD at both 0.01% and 1% in petrolatum, to the eyelash dye itself (tested semi-open, as is), and to several azo dyes. The authors concluded she had probably been sensitised through azo dyes in nylon stockings, with PPD cross-reacting. SCOPE LIMITS: n=1; and the paper's assertion that PPD in eyelash dye 'is illegal' reflects the 2006 legal position — Annex III entry 8b (source 4) now permits PPD up to 2% in professional-use-only eyelash colouring products in GB, so that specific legal statement is out of date. TIER CORRECTION ON VERIFICATION (tier 3 -> tier 4): PubMed's publication type for this record is 'Case Reports' and n=1. The schema has no 'case-report' type, so it stays 'observational', but the tier now reflects that this is a single case. It had been carried at the same tier as the multi-thousand-patient IVDK and Bialystok analyses, which overstated it. The clinical detail, the 0.01% and 1% pet PPD positives and the semi-open test of the dye itself are all confirmed against the abstract.
  14. Department of Health and Social Care. Consultation: The licensing of non-surgical cosmetic procedures in England. Published 2 September 2023.Tier 2Supports: Consultation document setting out a PROPOSED three-tier model. Green: 'procedures with the lowest risk of complications. All practitioners are eligible to perform licensed procedures where they meet agreed standards.' Amber: 'procedures with medium risk of complications. Non-healthcare professionals must be licensed and have relevant oversight by a named regulated healthcare professional.' Red: 'procedures with the highest risk of complications' carried out only by regulated healthcare professionals in CQC-registered premises. Indicative placements in the consultation: superficial chemical peels and microneedling in green; medium-depth peels in amber; deep peels in red. SCOPE LIMIT, load-bearing: this is a proposal. No licensing scheme is in force in England as at 1 August 2026, and the August 2025 consultation response does not itself assign individual procedures to tiers — the placements above come only from the 2023 consultation document. Neither the consultation nor the response prescribes pre-service allergy testing. TIER CORRECTION ON VERIFICATION (tier 1 -> tier 2): this had been typed AND tiered identically to source 4, which is assimilated law in force. The schema has no separate type for a consultation, so the type stays 'regulatory' and the tier now carries the distinction: a proposal that has never been made law must not sit at the same tier as law in force. All tier placements re-verified verbatim against the live gov.uk consultation: green includes 'superficial chemical peels, where skin cells are removed from the epidermis' and microneedling; amber includes 'medium depth peels that involve full thickness destruction of entire epidermis into upper dermis'; red includes 'deeper chemical peels such as phenol peels'. Confirmed by direct check that the consultation contains no mention of allergy testing, patch testing or skin testing. ADDED ON VERIFICATION: the government response, 'The licensing of non-surgical cosmetic procedures in England: consultation response', was published on 7 August 2025; it does not name the green/amber/red tiers or assign individual procedures to them, and defers classification to a further public consultation. The tier placements quoted here therefore exist ONLY in the 2023 consultation document and have never been confirmed by government.