Standard photopatch testing with Waxtar, para-aminobenzoic acid, potassium dichromate and balsam of Peru.

194 patients were standard photopatch tested with Waxtar as is (coal tar 5%) and 161 patients were photopatch tested with para-aminobenzoic acid (PABA) 5% in alcohol, potassium dichromate 0.5% in petrolatum, and a mixture of balsams of Peru as is. The photopatches were irradiated with UVA. 40 patients (25%) had phototoxic reactions to Waxtar and 4 of them showed pigmentation after 7 days. Only a few patients had photocontact urticaria. 1 patient had a late-reaction to PABA and showed a cross-reaction to glyceryl PABA but a negative reaction to paraphenylenediamine (PPD) and benzocaine 5% in the standard test. No patients had positive photopatch reactions to potassium dichromate when irradiated with UVA. 2 patients had phototoxic reactions to balsam of Peru. None had photoallergic reactions. Standard photopatch testing is a time consuming procedure which creates problems both for the staff and for the patients. The yield of unexpected, relevant positive reactions is insignificant. From a cost-benefit view, photopatch testing is only warranted in cases giving rise to a clinical suspicion of photodermatitis.