Skin disorder characterized by red patches and silvery white scales, on head, elbows and knees. The condition is not serious, but patients find the conspicuous patches irksome. If the disease spreads there can be patches all over the body. The cause of psoriasis is not known exactly. Members of the patient’s family are more likely to contract it; it is usually improved by sunlight; there is no connection with certain foods. Microscopic examination has established that the disorder is connected with increased activity in the cells forming the base layer of the skin; it is not caused by a virus or bacterium, and is thus not infectious. There are various treatments, dependent upon the extent of the condition. Small patches can be treated with ointment containing tar, or corticosteroids. Large patches, or large numbers of small patches, are usually treated with ultraviolet light. These treatments relieve the symptoms, but the condition may recur.