On the fourth day of menstruation, the endometrial lining suddenly disappeared and came back on the fifth day, and the color was bright red. It is considered to be related to normal physiological phenomenon, endocrine disorders, and polyps. 1. Normal physiological phenomenon: the patient’s endometrium did not peel off on the fourth day of menstruation, the menstrual period suddenly disappeared, and on the fifth day of menstruation, part of the endometrium appeared to peel off again and vaginal bleeding, then it is considered to be a physiological phenomenon, do not need to be too nervous. 2. Endocrine disorders: If the patient is under pressure at work and study, often stay up late or combined with polycystic ovary syndrome and other gynecological endocrine diseases, due to irregular ovulation, so the patient will have irregular vaginal bleeding, usually can not stop by itself. 3. polyps: for patients with endometrial polyps, cervical polyps, the main manifestation of irregular vaginal bleeding, and generally can not stop by themselves. For the fourth day of menstruation suddenly disappeared on the fifth day and appeared bright red vaginal bleeding patients, it is recommended to the regular hospital gynecology consultation, improve ultrasound, sex hormones and other related examinations, clear cause of the disease in the doctor’s guidance and active treatment.