This study uses the psychological principle known as classical conditioning to try to improve the standard treatment of psoriasis. Classical conditioning is a process of behavioral modification in which a person learns to connect a certain response-in this case, improvement of psoriasis-with a new action, or stimulus-in this case, application of an inactive cream. The goal of this study is to show that people with psoriasis who are maintained on corticosteroid cream part of the time and an inactive (placebo) cream at other times show a lower incidence of relapse and a reduced severity of psoriasis that patients treated with that same (reduced) amount of medication administered all the time.