Sudden and severe hair loss may be related to physiological factors such as stress, nervousness and anxiety, as well as pathological factors such as folliculitis, seborrheic dermatitis and baldness. 1. Physiological factors: prolonged stress and anxiety, lack of sleep, overtime work and late night, etc., cause hair growth stagnation, which may lead to sudden and severe hair loss. 2. Pathologic factors: (1) Folliculitis: mainly caused by bacterial infection, low immunity, trauma, obesity, etc., often showing red papules centered on hair follicles, accompanied by itching and pain, etc., damage to hair follicles may lead to sudden and severe hair loss. (2) Seborrheic dermatitis: mainly caused by bacterial infection, heredity, diet, immune dysfunction, etc., often showing erythematous rash, greasy, flaky, itchy, etc., which may lead to sudden and severe hair loss. (3) Patchy baldness: mainly caused by immune factors, heredity, mental factors, allergies, etc., often showing patchy hair loss, which may lead to the emergence of sudden and severe hair loss. Therefore, if sudden and severe hair loss occurs, it is recommended to consult a doctor in time to find out the cause and then target treatment under the doctor’s guidance.