Sudden and severe hair loss may be caused by physiological reasons, or pathological reasons such as androgenetic alopecia, scalp folliculitis, baldness, ringworm and other diseases. 1. Physiological reasons: such as suddenly experiencing great mental stimulation, there will also be a sudden severe hair loss. 2.Pathologic causes: (1) Androgenetic baldness: genetic factors, elevated androgen levels and other factors may induce androgenetic alopecia, causing patients to experience symptoms such as thinning hair and sudden severe hair loss. (2) Scalp folliculitis: Sudden and severe hair loss may be caused by scalp folliculitis. If there is no good scalp hygiene care, so that the scalp follicles are infected with staphylococcus aureus and other germs, it is easy to induce scalp folliculitis. Patients may be accompanied by scalp itching, pimples and other symptoms. (3) Patchy baldness: the cause of the disease is not yet clear, it may be related to immune factors, heredity and other factors, and secondly, environmental factors, neuropsychiatric factors may also induce patchy baldness, leading to sudden and severe hair loss. (4) Tinea capitis: caused by fungal infection of the scalp and hair, when the disease develops to a certain stage, it will also cause sudden and severe hair loss, accompanied by symptoms such as erythema and dandruff. There are many reasons for sudden hair loss, and patients are advised to go to the hospital to clarify the cause of the disease.