Patchy baldness is a sudden onset of limited patchy hair loss. Hair loss at the back of the head is mostly related to emotional stress, genetic factors and autoimmunity. 1. Emotional stress: If the patient is under long-term mental stress, sleep disorder, frustration, depression and other states, causing mental stress, it can aggravate or induce baldness on the back of the head. 2. Genetic factors: Pemphigus vulgaris has a certain genetic basis, and patients with a history of pemphigus vulgaris in their family will have a higher possibility of developing the disease. 3. Autoimmune factors: Due to the dysfunction of T-lymphocytes of the immune system, specific immune reaction is generated, which causes a large amount of hair loss and forms patchy baldness. Patients with patchy baldness on the back of the head should consult a doctor in time to identify the causes or triggering factors and actively cooperate with the doctor’s treatment.