The scalp has blood scabs considering the following diseases may be: 1, herpes zoster: usually occurs in the unilateral scalp, along the nerve line in a unilateral band distribution, did not exceed the midline, the disease is caused by varicella-herpes zoster virus infection, can appear blood blisters, when the blood blisters dry up can form a blood scab. 2, seborrheic dermatitis: because accompanied by severe itching, can cause scratching after the appearance of blood scabs. The cause of seborrheic dermatitis may be related to allergy to sunlight and ultraviolet radiation, viral infection or poor nutritional status, vitamin deficiency, etc. 3. Psoriasis vulgaris: mainly due to polygenic dominant inheritance, excessive scratching causes a secondary rash with blood crusts.