A sudden bald patch of hair may be caused by spot baldness, ringworm, alopecia areata folliculitis and so on. 1. Patch baldness: hair suddenly bald piece may be caused by patch baldness, patch baldness is a kind of head suddenly occurring limited patchy baldness, the diseased area of the skin in addition to the absence of hair, there are no other abnormalities. It may be related to mental stress, family heredity, endocrine disorders, immune inflammation and so on. 2. ringworm of the head: hair suddenly bald piece may be caused by ringworm of the head, ringworm of the head is usually divided into yellow ringworm, white ringworm, black spot ringworm and pus ringworm. Clinically, ringworm is the most common, manifesting itself as a soybean-sized yellow ringworm scabs, forming atrophic scars after healing, leaving permanent baldness. The yellow scab is thicker, often prone to bacterial secondary infection, there is a special odor, self-conscious itch. 3. Alopecia areata folliculitis: a destructive, chronic inflammation of the hair follicle that can cause scarring alopecia. Mostly seen in the head seborrheic dermatitis patients, can involve any hairy parts, can also cause progressive scarring alopecia. The patient’s hair suddenly bald piece, it is recommended to go to the hospital in a timely manner, to clarify the cause of the disease under the guidance of the doctor reasonable treatment.