A large amount of dandruff just after washing your hair may be caused by seborrheic dermatitis, scalp psoriasis, ringworm of the scalp and other causes. 1. Seborrheic dermatitis: seborrheic dermatitis is a chronic inflammatory skin disease, seborrheic dermatitis is a typical symptom of skin erythema, greasy scales, accompanied by varying degrees of itchiness, which can appear after washing the head there is a lot of dandruff phenomenon. 2. Scalp psoriasis: psoriasis lesions can occur on the scalp, manifested as erythema of the skin, erythema with large scales, so there is a large amount of dandruff after washing the hair. 3. Tinea capitis: Tinea capitis refers to a dermatophyte infection that involves the hair and scalp, which can lead to white scales covering the scalp, and thus there is also a lot of dandruff after washing the hair. There may be other reasons why you have a lot of dandruff just after washing your hair, and you should go to the hospital in time to avoid delaying your condition.