A sudden bald patch on the head is often considered as spot baldness, bald folliculitis or ringworm, and should be detected and treated as early as possible. 1. Patch baldness: it may be related to mental, emotional stress, heredity, endocrine disorders, etc. It is manifested as the sudden appearance of oval or round hair loss area with varying number of hair loss, the affected area has smooth skin without inflammation, scaling and scarring, and some of them can be cured by themselves. 2. Bald folliculitis: when folliculitis occurs in the scalp hair follicles, hair loss and scarring may remain after healing. 3. Tinea capitis: when tinea capitis occurs, there will be cluster red papules at the beginning, which can be enlarged in all directions, covered with grayish-white scales, forming “mother and child spot”, and the sick hair can be broken off at 2-4mm above the scalp, which will look like a piece of baldness, and will not result in permanent baldness; when tinea capitis pustulosa occurs, it will destroy the hair follicles and leave permanent baldness. When you find a piece of baldness on your head, it is recommended that you seek medical attention as soon as possible to identify the cause of the condition and follow the doctor’s instructions for treatment.