The causes of dandruff are seborrheic dermatitis and scalp-type psoriasis. 1. Seborrheic dermatitis: the etiology of the disease is still not very clear, and it may be related to Malassezia colonization, increased lipids, impaired skin barrier function, immune response and individual susceptibility. When patients suffer from seborrheic dermatitis, the sebum secretion of the scalp increases, which will cause inflammation of the scalp, and then there is an increase in dandruff, accompanied by itching symptoms. 2. Scalp-type psoriasis: the cause of the disease is still unclear, and may be related to genetic, immune and other factors. The biggest characteristic of psoriasis is a lot of flakes, and the head is the most common part of psoriasis, which will have red spots on the scalp, flakes, and tufts of hair. Usually pay attention to protect the scalp, use warm water when washing hair, do not scratch the scalp, if excessive dandruff occurs, it is recommended to consult a doctor in time to avoid aggravation of the condition.