The difference between psoriasis and seborrheic dermatitis lies in the rash manifestations, self-conscious symptoms, disease duration and related factors, as follows: 1. Rash manifestations: psoriasis can appear as well-defined erythematous patches or plaques with silvery-white scales, and scraping out the scales can reveal the phenomenon of thin film and punctate bleeding. In the case of seborrheic dermatitis, there are usually pale red patches covered with fine bran-like scales; 2. Self-perceived symptoms: psoriasis can be accompanied by itching or not, and seborrheic dermatitis can be accompanied by mild itching; 3. The most common of these is the seborrheic dermatitis in young and middle-aged people, which gradually decreases after old age, and its onset is more closely related to diet, endocrine secretion, skin cleanliness and hygiene factors.