PPD Allergy — SCE Dermatology MCQ
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Correct answer: B — PPD cross-reacts with para-aminobenzoic acid (PABA in sunscreens), Benzocaine (local anaesthetic), Sulfonamides, azo dyes in textiles, and temporary black henna tattoos
The correct answer is B: PPD cross-reacts with para-aminobenzoic acid (PABA in sunscreens), Benzocaine (local anaesthetic), Sulfonamides, azo dyes in textiles, and temporary black henna tattoos. Paraphenylenediamine is a para-amino aromatic amine, and structurally related para-amino compounds share the same immunogenic epitope, producing clinically relevant cross-sensitisation once a patient is patch-test positive to PPD. This is why UK patch test clinics and the British Society for Cutaneous Allergy specifically counsel PPD-allergic patients to avoid PABA sunscreens, ester-type local anaesthetics such as benzocaine, sulfonamide-containing products, azo dyes in dark textiles, and black henna temporary tattoos, which themselves contain high-concentration PPD and are a common route of primary sensitisation. Restricting advice to hair dyes alone would leave the patient exposed to these other significant allergen sources and risk further flares.
Reference: https://www.nice.org.uk/guidance/conditions-and-diseases/skin-conditions