What causes dark red blood in menstruration?

Dark red blood in menstruation is typically caused by the blood being older and oxidizing as it exits the body. This can happen when the blood takes longer to leave the uterus and is exposed to air for a longer period of time. It can also be a sign of a heavier flow or a slower flow, which can cause the blood to appear darker in color. In some cases, dark red blood may also be a sign of an underlying health issue such as endometriosis or fibroids. If you are concerned about the color of your menstrual blood, it is always best to consult with a healthcare provider for further evaluation and guidance.