Late reactions to patch test preparations with reduced concentrations of p-phenylenediamine: a multicentre investigation of the German Contact Dermatitis Research Group

p-Phenylenediamine (PPD) 1% in petrolatum has been shown in a prospective study to elicit late reactions in 1.5% of routine patch tests, which may be indicative of patch test sensitization. Objectives. To assess the frequency of late reactions to reduced PPD patch test concentrations. Methods. In 1838 patients, PPD was tested at three concentrations (0.5% pet., group I; 0.4% pet., group II; and 0.35% pet., group III). Patch tests were read on D1 (D2) to D3 (D4); additional late readings were performed on D7, D14, and D21. Patients who were not able to return for all scheduled late readings were telephoned on D7, D14, and D21, and questioned about a reaction at the patch test sites. Results. Data of 1666 patients (1069 women and 597 men) were eligible. Late reactions were observed in 9 patients, 3 in group I (0.49%) and 5 in group II (0.63%). In 7 of 8 of the patients with late reactions, patch tests were applied for 48 hr. On retesting, 4 of 5 patients became positive at D2 or D3. Conclusions. The occurrence of late reactions to PPD may be influenced by patch test concentration and duration. PPD 0.4-0.5% pet. may cause late reactions indicative of active sensitization.