The main causes of large dandruff on the scalp include scalp chaffing, scalp psoriasis, seborrheic dermatitis, and so on. 1. Scalp chafing: also called dry seborrhea, usually caused by infection with Sporothrix mycoides, the common clinical manifestation is diffuse, large, chaffy scales on the head, mostly accompanied by itching. With the aggravation of symptoms, it may also lead to hair loss and thinning. 2. Scalp psoriasis: its patients usually appear in the scalp lesions, but also often combined with the body limbs scaly erythema. The common clinical manifestations are infiltrative, well-defined erythema on the head with thick scales, hair in bundles and accompanied by large dandruff. 3. Seborrheic dermatitis: The scalp is an area rich in hair follicles and sebaceous glands. When the sebum secretion increases or the chemical composition of sebum changes, can lead to the scalp surface of the bacterial flora imbalance, and then cause seborrheic dermatitis of the scalp. Sweat impregnation, sebum corruption, physical and chemical stimulation and other local factors, can aggravate the symptoms of seborrheic dermatitis, dandruff increase, itchy, and in severe cases, dandruff will also appear to expand into a greasy shape, accompanied by vesicles, oozing, crusting and so on. If there are large pieces of dandruff on the scalp and other uncomfortable symptoms, it is recommended to consult a doctor in a timely manner, and follow the doctor’s instructions for symptomatic treatment.