If there are large and numerous dandruff patches on the scalp, consider seborrheic dermatitis on the one hand. When seborrheic dermatitis develops to a severe stage, there will be a reaction of large scales and large flakes of scales. If it is scalp psoriasis, this similar symptom will also appear, but scalp psoriasis appearing with large pieces of dandruff may be accompanied by characteristic hair changes, and this characteristic hair is bundled hair, because the scalp of early psoriasis and scalp seborrheic dermatitis are really not easy to distinguish at the time of diagnosis.