Hair sideburns suddenly bald is usually caused by spot baldness, ringworm and other diseases. Patch baldness: the cause of the disease is not clear, with heredity, autoimmune and other factors, can occur in any area of the scalp, such as the top of the head, sideburns, etc., the patient has no special feeling, can be accidentally found on the top of the head, sideburns and other areas of the hair fast, a large number of loss, and the affected area of the skin is smooth, no inflammation. Ringworm of the head: is caused by fungal infection, when the infected part is located in the temples, local erythema, pimples, pustules and other lesions, and can be accompanied by different degrees of hair loss, scalp itching and so on. In addition, there are many other reasons that may cause hair sideburns suddenly bald, it is recommended to go to the hospital in a timely manner to identify the cause of the disease, and then receive treatment as soon as possible.