Paraphenylenediamine (PPD) contact allergy turned up in 4.3% of patch-tested patients, and most products marketed in the UK as "PPD-free" still contained closely related aromatic amines capable of triggering equivalent reactions, according to a retrospective review published online September 22 in Contact Dermatitis.

Zara Ali of University Hospital Southampton, England, served as corresponding author on the study, which drew on patch test outcomes from January 2018 to January 2025. The researchers aimed to characterize the clinical picture, cross-reactivity, and postdiagnosis outcomes of PPD allergy.

The cohort comprised 1306 patients patch tested with a commercial allergen panel. PPD was tested at 1% in a petrolatum base within the baseline series, with an additional hairdressing series applied based on clinical suspicion. The team extracted allergy history, occupation, probable trigger, and symptom duration from electronic records, then administered a telephone questionnaire covering symptom improvement, avoidance success, and occupational impact. A structured web search in October 2025 — reviewing the top 50 hits per search term — identified "PPD-free" dyes and eyebrow/eyelash tints sold in the UK; their listed ingredients were cross-referenced against PPD, para-toluenediamine, aminophenols, and related compounds.

Fifty-six patients tested positive. The mean age at diagnosis was 49 years, and 82% were women. Hair dye led the exposures, reported by 43 patients (77%). Eight patients (14%) — all hairdressers or hairdressing students — had occupational exposure.

Diagnostic delay was substantial. Patients reported a mean symptom duration of 4.9 years before diagnosis. Clinicians documented moderate or severe disease in 54 patients (96%), with eczematous dermatitis the most frequent presentation (n = 51; 91%).

Cross-reactivity was clinically meaningful. Among 37 patients additionally tested for para-toluenediamine, roughly a quarter (27%) reacted positively to it. Follow-up data came from 31 patients (55%) reached by telephone: 24 (77%) reported complete or near-complete remission after avoiding PPD-containing products. All five patients with occupational exposure reached at follow-up had changed careers or left work.

The product review exposed a labeling gap. Of seven "PPD-free" permanent dyes, only one lacked PPD, para-toluenediamine, aminophenols, and derivatives. Of three "PPD-free" brow/lash tints, two still contained para-toluenediamine and aminophenols; the third prompted a UK product safety report for marketing a para-toluenediamine-containing product as "PPD-free."

"Improved regulatory oversight and mandatory disclosure of all aromatic-amine derivatives on product labelling are required to protect consumers and support clinicians in advising patients," the authors wrote.

"Broader advocacy for clearer labelling and inclusion of aromatic-amine derivatives in EU and UK cosmetic safety databases is warranted. Development of validated patient-education materials and occupational-screening protocols could further reduce disease burden," they added.

The retrospective design, dependence on historical records, and incomplete patch testing that did not cover every potentially cross-reactive allergen limited the findings. The product review relied on ingredient data published on brand and retailer websites, which may not reflect proprietary formulation details.

No specific funding was reported, and the authors disclosed no relevant conflicts of interest.

With avoidance driving remission in more than three-quarters of patients reached at follow-up, the study's call for mandatory aromatic-amine disclosure and occupational screening points toward next steps in reducing the diagnostic delay and disease burden this cohort experienced.