A small piece of hair loss may be caused by baldness, fungal infection, seborrheic dermatitis and other factors, and you should consult a doctor in time to find out the cause of the disease. 1. Patchy baldness: Patchy baldness is limited patchy hair loss, and autoimmune, genetic factors, endocrine disorders and other factors, patchy baldness will lead to limited hair loss on the scalp, usually patchy hair loss is the main hair loss, hair loss area without scarring, no inflammation. 2. Fungal infection: a small piece of hair missing on the head may also be a factor of fungal infection, common tinea versicolor, manifested as limited hair loss, the appearance will be accompanied by dry tinea versicolor, with symptoms such as dandruff. 3. seborrheic dermatitis: a small piece of hair on the head may also be seborrheic dermatitis caused by seborrheic dermatitis is a localized chronic inflammatory dermatosis, which will lead to a small piece of hair loss on the head, accompanied by localized erythema, flaking symptoms. This symptom alone is difficult to determine the disease, there may also be other causes. It is recommended that the patient consult a doctor to identify the cause of the disease and give targeted treatment.