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Menstruation
Reviewed by Medicinsk Expert•Last updated: 2026-10-22•Women

Menstruation

Menstruation is a normal monthly cycle where the uterus sheds its lining, often accompanied by physical and emotional symptoms.

What is menstruation?

Menstruation, also called a period, is normal vaginal bleeding that happens as part of the monthly cycle in women and girls. Every month, the body prepares for pregnancy. If pregnancy does not happen, the uterus (womb) sheds its lining. This blood and tissue leave the body through the vagina.

What is the menstrual cycle?

The menstrual cycle is the monthly process the body goes through to prepare for pregnancy. It is counted from the first day of one period to the first day of the next. Most menstrual cycles last about 28 days, but cycles can be shorter or longer and still be normal.

When will my period start?

Most girls start having a period between ages 9 and 15, but some may start earlier or later. A period usually lasts three to seven days and can be light or heavy. It may take a few years to become regular.

Your period may change during times that affect hormones, such as after childbirth or while breastfeeding. Periods usually continue until menopause, which most often happens between ages 45 and 55.

What are the symptoms of menstruation?

In addition to vaginal bleeding, you may have:

  • Cramping pain in the lower abdomen (belly) or pelvis
  • Lower back pain
  • Bloating
  • Sore breasts
  • Food cravings
  • Mood swings or irritability
  • Headaches or fatigue

Premenstrual syndrome (PMS) is a group of physical and emotional symptoms that can happen in the days before a period starts. Many women have some PMS symptoms, which usually go away after their period begins.

What are menstrual irregularities?

Menstrual irregularities are changes in the usual menstrual cycle. These may include missed periods, irregular periods, or heavy bleeding. Common menstrual irregularities include:

  • Amenorrhea means not having a period.
  • Oligomenorrhea means having periods that happen less often.
  • Menorrhagia means very heavy menstrual bleeding.
  • Prolonged menstrual bleeding occurs when periods regularly last longer than 8 days.
  • Dysmenorrhea refers to painful periods that may include severe cramps.

Keep track of your period each month. This can help you understand your usual cycle, know when to expect your next period, and notice changes. Talk with your health care provider if you notice major changes in your menstrual cycle, very heavy bleeding, or severe pain. These may be signs of other health problems that need treatment.

Frequently Asked Questions

Heavy menstrual bleeding, or menorrhagia, is typically defined as soaking through one or more sanitary pads or tampons every hour for several consecutive hours, passing clots larger than a quarter, or bleeding that lasts longer than seven days. If your bleeding interferes with daily activities or causes fatigue due to iron loss, you should consult a healthcare provider.
Irregular periods in adolescents are often due to the immaturity of the hypothalamic-pituitary-ovarian axis, which can take up to two years to regulate after menarche. Other common causes include stress, significant weight changes, excessive exercise, and polycystic ovary syndrome (PCOS). Persistent irregularity beyond two years or missed periods should be evaluated to rule out underlying hormonal imbalances.
Reducing sodium intake can help minimize bloating, while limiting caffeine and alcohol may reduce breast tenderness and mood swings. Increasing consumption of complex carbohydrates, calcium-rich foods, and omega-3 fatty acids has been shown to help stabilize mood and reduce cramping. Regular moderate exercise also helps alleviate physical and emotional PMS symptoms.
Yes, combined oral contraceptives can significantly reduce menstrual flow and alleviate dysmenorrhea (painful periods) by thinning the uterine lining and suppressing ovulation. They are a first-line treatment for many women with heavy or painful periods, but they are not suitable for everyone, particularly those with risk factors for blood clots or certain types of headaches.
Source: MedlinePlus, National Library of Medicine

MedlinePlus brings together authoritative health information from the National Library of Medicine (NLM), the National Institutes of Health (NIH), and other government agencies and health-related organizations.

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