Periods

This page is reference information compiled from the cited sources. It is not medical advice. For any decision about health, diagnosis or care, consult a qualified professional.

What it is

Menstruation is also known as a period. It is the regular discharge of blood and mucosal tissue from the inner lining of the uterus through the vagina. The menstrual cycle is characterized by the rise and fall of hormones. Menstruation is triggered by falling progesterone levels and is a sign that pregnancy has not occurred. Feminine hygiene products are used to maintain hygiene during menses. Periods stop during pregnancy and typically do not resume during the initial months of breastfeeding. Menstruation, and with it the possibility of pregnancy, ceases after menopause.

Key facts

The first period is known as menarche and usually begins between the ages of 11 and 13, though starting as young as eight is considered normal. The average age of the first period is generally later in the developing world and earlier in the developed world. The typical length of time between the first day of one period and the first day of the next is 21 to 45 days in young women and 21 to 35 days in adults, with an average often cited as 28 days. In the largest study of menstrual app data, the mean menstrual cycle length was 29.3 days. Bleeding typically lasts two to seven days. The average volume of menstrual fluid is 35 ml with 10–80 ml considered typical, and about half of menstrual fluid is blood. During their menstrual period, 38% of all women reported not being able to perform all their regular daily activities. Symptoms that interfere with normal life in advance of menstruation are called premenstrual syndrome (PMS), experienced by 20 to 30% of women, with 3 to 8% experiencing severe symptoms. These symptoms include acne, tender breasts, bloating, feeling tired, irritability, and mood changes. Other symptoms some women experience include painful periods, with estimates between 50 and 90%, and heavy or abnormal bleeding. A lack of periods is known as amenorrhea.

When to seek professional help

Severe symptoms that disrupt daily activities and functioning may be diagnosed as premenstrual dysphoric disorder. When severe pelvic pain and bleeding suddenly occur or worsen during a cycle, this could be due to ectopic pregnancy and spontaneous abortion, which is checked by using a pregnancy test because ectopic pregnancies can be life-threatening. A lack of periods, known as amenorrhea, is when periods do not occur by age 15 or have not re-occurred in ninety days. Heavy menstrual bleeding, occurring monthly, can result in anemia. In one study, premenopausal women with symptoms of iron deficiency were given endoscopies, and 86% had gastrointestinal disease and were at risk of being misdiagnosed simply because they were menstruating.

Source: Menstruation (CC BY-SA 4.0 (Wikipedia)), retrieved 2026-08-27.