Why is menstrual blood black?

There are two possible explanations for dark-colored menstrual blood during menstruation. First, the menstrual flow may be relatively light; in such cases, the blood often contains a large amount of shed endometrial tissue, which—upon oxidation—turns darker, resulting in the appearance of blackish menstrual blood.

Second, excessive menstrual bleeding may lead to rapid clot formation; these clots typically appear dark red or even deeper in color. During menstruation, women are advised to maintain a positive emotional state and avoid consuming excessively cold foods.

If dark-colored menstrual blood persists over a prolonged period, individuals—especially those with access to healthcare—should consider visiting a reputable hospital for evaluation to rule out potential pathologies, such as cervical or endometrial abnormalities. For women experiencing menorrhagia (excessively heavy menstrual bleeding), particular attention should be paid to the cervix, myometrium, and endometrium; any identified abnormalities require targeted treatment.