The basic damage of psoriasis vulgaris tough starts as a red papule or rash. The safest and most effective way to check for psoriasis is based on the characteristics of the rash, the location and duration of the disease, as follows: 1. Rash characteristics: Initially an inflammatory red papule, about the size of a corn to a green bean, which gradually expands or fuses to become a brownish-red plaque with clear borders, surrounded by an inflammatory red halo, with obvious basal infiltration and covered with multiple layers of dry grayish or silvery-white scales. Gently scrape away the surface scales, gradually reveal a layer of light red shiny translucent film, called film phenomenon. If the film is scraped away again, small bleeding spots will appear, which is called punctate bleeding phenomenon. White scales, shiny film and punctate hemorrhage are important features for the diagnosis of psoriasis, which is called the triad of signs. The lesions are dotted, coin-shaped, map-like, ring-like, band-like, generalized, seborrheic dermatitis-like, eczema-like, oyster shell-like, flat moss-like, chronic hypertrophic, wart-like, etc. 2, the site of prevalence: scalp, extensor side of the limbs, symmetrical distribution; finger (toe) nail and mucous membrane can also be invaded, a few can be seen in the axilla and groin and other folds, palmoplantar rarely occur. 3.Course of disease: chronic course, recurrent. Most patients are heavy in winter and light in summer, and a few patients are heavy in summer and light in winter. The course of the disease is generally divided into three stages: ① progressive new rash constantly appear, the old rash expanding, thick scales, inflammation is obvious, itching is significant, skin sensitivity increased, may appear isomorphic reaction; ② stationary phase without new rash, the old rash does not recede; ③ degenerative phase of inflammation subsides, scales reduce, the rash shrink and flatten, the surrounding light halo, and finally left temporary hypopigmentation or hyperpigmentation.