Skin irritation by dithranol cream. A blind study to assess the role of the cream formulation

In connection with a national cost-effective evaluation study of short contact dithranol therapy for psoriasis, the question arose whether dithranol cream irritation is influenced by constituents of the vehicle. To establish the role of the different components of the vehicle in the mechanism of dithranol irritation, the dithranol 3% cream used in the evaluation study and its vehicle with nine different combinations of its components were tested in a blind study. The creams were applied for 15, 30 and 45 min on the backs of 12 healthy volunteers. Irritation was scored as erythema by visual and colorimeter scoring. The dithranol creams with salicylic acid among their stabilizers showed 42% more irritation than the dithranol creams with only sorbic acid or no stabilizers at all. Stability tests showed no significant degradation of dithranol in the two less irritating creams when kept at 4 degrees C for 11 months. Salicylic acid in the cream aggravates dithranol-induced erythema.