The first menstrual period of puberty is called menarche. Bleeding during menarche may be irregular and unpredictable at the onset, but eventually the cycle becomes rhythmic until menopause. Menopause is the cessation of menstruation. The typical menstrual cycle lasts 26 to 35 days. Bleeding varies from 3 to 7 days, but the amount is usually no more than 2 to 4 ounces.

Menstrual blood contains mucus and destroyed cellular tissue from the endometrium that does not coagulate. However, when exposed to the air it has a fleshy odor and can become offensive.