Black membranes in menstrual blood are generally normal and are caused by the shedding of the lining of the uterus. A woman’s menstruation is actually the shedding of the endometrium, not just the discharge of blood. Stimulated by hormones, the endometrium undergoes cyclic growth and shedding. During menstruation, this lining is discharged from the vagina, and blood is usually intermingled with the membrane-like material. When oxidized in the air, these substances take on a black color. If a woman does not experience any special symptoms other than this phenomenon, there is no cause for concern. If there are other physical discomforts or other obvious abnormalities in menstruation, it is recommended to consult a doctor in time, complete the relevant examinations, and clarify the cause of the disease under the guidance of a professional doctor, so as to provide targeted treatment.