Do excoriations in psoriasis delay or prevent the effect of topical treatment?

Topical treatment of a number of out-patients with psoriasis vulgaris resulted in reduced induration and diminished thickness of the layer of scales but complete involution was not obtained. A sequential photographic study of the macroscopic appearance of the lesions over a 3-month period of treatment revealed that artificially produced excoriations and a horny layer without scales were prominent features. The view is put forward that the cutaneous reaction to the injury probably elicited by the excoriations, together with an unsatisfactory treatment, may give rise to tissue changes which counteract the effect of topical treatment.