Severe hair loss can be caused by vitamin B deficiency. The B vitamins include vitamin B1, vitamin B2, vitamin B6, and vitamin B12. Vitamin B deficiency may lead to malnutrition, which has an effect on the hair follicle’s ability to produce hair and may lead to hair loss. One of the vitamin B6 deficiencies, excessive oil production, may cause irritation to the hair follicles, leading to hair loss. In addition to vitamin B deficiency, severe hair loss may also be caused by mental stimulation, genetic factors, and lifestyle habits. If hair loss occurs, it is recommended to go to the hospital for relevant examinations to identify the causes and treat the symptoms under the guidance of the doctor.