There has been no dandruff, the sudden appearance of dandruff may be ringworm of the head, seborrheic dermatitis, psoriasis and other reasons. 1. Tinea capitis: Tinea capitis is a superficial fungal infectious disease that occurs in the scalp and hair area, which can be manifested as scales, papules and pustules. Therefore, there has been no dandruff can suddenly appear dandruff. 2. Seborrheic dermatitis: If seborrheic dermatitis occurs on the scalp and there has been no dandruff, dandruff can suddenly appear. It may be related to heredity, psychology and the proliferation of Malassezia bacteria, etc. It may show erythema and greasy scales on the scalp, and may be accompanied by itching. 3. Psoriasis: There has been no dandruff, but the sudden appearance of dandruff may also be psoriasis. The cause of psoriasis is still unclear, and it can be manifested as repeated episodes of scaly erythema, papules, plaques and so on. There have been no dandruff, the sudden appearance of dandruff may also be other reasons. It is recommended to go to the hospital in time, to clarify the cause of the disease, and under the guidance of the doctor to carry out active treatment.