Addressing the conundrums of p ‐phenylenediamine hair dye allergy by applying Friedmann’s principles of contact sensitization

SummaryIn the first conundrum, permanent hair dyeing uses aromatic amines such asp‐phenylenediamine (PPD), whose oxidation is pivotal to the dyeing process, but also generates potent allergens. Despite prolonged industry effort searching for safer alternatives, hair dyeing is still reliant on this type of aromatic amine. In the second conundrum, patch testing with 1% PPD remain s the most useful screen for hair dye contact allergy. However, there is a very small but real risk of actively sensitising the patient. Lowering the PPD concentration below 1% significantly reduces test sensitivity and diagnostic utility. Here we argue that by applying Friedmann's principles of c ontact sensitisation each conundrum can be addressed from a new perspective. These principles indicate that where th...

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