Psoriasis, commonly known as psoriasis, is a common chronic inflammatory skin disease that is prone to recurrence. The characteristic lesions are red papules or plaques covered with multiple layers of silvery white scales. The disease is most common in young and middle-aged people, more common in men than in women, more common in the north than in the south, prone to or aggravated in spring and winter, and mostly relieved in summer and autumn. The cause and pathogenesis are not fully understood. Studies have found that the onset of this disease is related to genetic factors, infection with streptococci, abnormal immune function, metabolic disorders and endocrine changes. There are four types clinically: common type, pustular type, erythrodermic type and arthritis type. Common psoriasis is the most common and the condition is mild. The disease is chronic and prone to relapse after recovery.