Menstruation is when the lining of the uterus sheds, breaking down into blood. This blood then leaves the body through the vagina. It is also known as a period.

Periods usually last around 3–7 days. During this time, a person who is menstruating bleeds from the vagina. They may also experience other symptoms, such as cramping.

Menstruation stops when someone is pregnant, so having a period means a person is not pregnant. It also marks the beginning of a new menstrual cycle. This is the cycle of fertility that affects most females from their teenage years through to menopause, when periods stop.

In this article, learn more about what menstruation is, when it starts, the phases of the menstrual cycle, and how to manage them.

A note about sex and gender

Sex and gender exist on spectrums. This article will use the terms, “male,” “female,” or both to refer to sex assigned at birth. Click here to learn more.

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Menstruation occurs when the lining of the uterus sheds, turning into blood. This blood then flows out of the body through the vagina. It is also known as a period.

Periods happen due to the menstrual cycle. This is the rise and fall of hormones, such as estrogen and progesterone, that influence female fertility over the course of around 21–35 days.

Fertility peaks roughly halfway through the cycle with ovulation, which is when the ovaries release an egg. This causes the uterine lining to thicken in preparation for a potential pregnancy. If no sperm fertilizes the egg, the uterus sheds this lining, and the cycle begins again.

The length of someone’s cycle, duration of their periods, and the day they ovulate vary from person to person. Sometimes, it also varies from cycle to cycle.

A person’s first period indicates that the menstrual cycle has begun. Doctors refer to this as menarche. For most females, it occurs between the ages of 9–15, with the average age being 12.4 years.

A period is one of the signs of puberty, which is the beginning of a journey toward sexual maturity. This likely means that it is possible to get pregnant.

However, a person can become pregnant from the first time they ovulate, which means it is possible to get pregnant before the first period.

Other signs of puberty include:

  • growth spurts
  • increased fat on the hips, thighs, and buttocks
  • developing more body hair, especially on the legs and under the arms
  • growing pubic hair

Most young people develop breasts about 2.5 years before menarche. If a person does not get their first period within 5 years of breast development, doctors consider this delayed menarche.

Learn more about the first period and what to expect.

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Doctors generally divide the menstrual cycle into two distinct phases.

Follicular phase

During the last few days of a period, the pituitary gland stimulates the production of follicle stimulating hormone (FSH). This triggers the development of eggs in the ovaries.

Next, luteinizing hormone stimulates the release of the egg from the ovaries into the fallopian tubes. The lining of the uterus begins to thicken to prepare for a potential pregnancy.

A person becomes pregnant when sperm from a male fertilizes the egg. Sperm can live in the reproductive tract for several days, so it is possible to become pregnant before and slightly after ovulation.

Ovulation is not always predictable and can happen early or late. So, it is theoretically possible for someone to become pregnant at any point in the menstrual cycle.

Luteal phase

After ovulation, the luteal phase begins. If sperm fertilizes the egg, it will travel down the fallopian tube and into the uterus, where it will attempt to embed in the uterine lining.

If sperm does not fertilize the egg, it will travel into the uterus. The lining will then shed, breaking down into blood and taking the unfertilized egg with it.

A period generally lasts about 5 days, with a heavier flow on the first 2 days. The amount of blood loss is usually around 5–12 teaspoons.

When menstruation begins, it marks the beginning of a new follicular phase, and the cycle begins again.

In addition to bleeding, people who are about to menstruate can experience a collection of symptoms known as premenstrual syndrome (PMS). These can act as signs that a period is about to begin.

PMS can vary, and not everyone experiences it. If they do, they may have any of the following:

  • cramping and pain
  • diarrhea
  • bloating
  • breast swelling, soreness, or tenderness
  • headache
  • fatigue
  • mood changes
  • food cravings
  • lower back pain

It is important to note that extreme pain during a period is not normal, and may signal an underlying health condition. Similarly, severe mood changes or depression that only occurs before a period is also not typical for PMS. A person should consult a doctor if either occurs.

Learn more about the signs a period is coming.

There are a variety of ways to manage menstruation with various products people can use to catch or absorb the blood. They include:

Disposable menstrual products

  • Sanitary pads or napkins: These are thin, absorbent pads or napkins that someone places inside their underwear, changing regularly. They come in different shapes, sizes, and thicknesses to suit someone’s needs.
  • Tampons: These are cylindrical wads of absorbent material that a person inserts into the vagina. These also come in different sizes and absorbencies.

Reusable menstrual products

  • Cloth pads: These are similar to sanitary pads but consist of fabric such as cotton or flannel. A person fastens them inside their underwear and changes them in the same way as sanitary pads, but rather than disposing of them, a person can wash and reuse them month to month.
  • Reusable underwear: These garments are similar to regular underwear, but have an inbuilt absorbent layer of material. People can wash them in the same way as their usual underwear and reuse them. They are also known as “period panties”.
  • Menstrual cups: Menstrual cups are small, silicone cups that a person inserts into the vagina. Instead of absorbing blood, the cup catches the blood. A person then pours the blood away and reinserts. When a period finishes, they can sterilize the cup and reuse it for the next period.
  • Blanket: These are large pieces of cloth that people place between the legs during sleep. People can wash and reuse them each cycle.

When using a period product, people should always follow its instructions. This will reduce the chance of leaks.

Irregular periods occur when a menstrual cycle is much shorter, longer, or more changeable than average.

To an extent, cycle variations are common, especially during puberty or perimenopause. While health organizations often quote 28 days as the average cycle length, only about 16% of people have a menstrual cycle that is this length, according to a 2020 study.

To receive a medical diagnosis of irregular periods, or oligomenorrhea, periods have to be more than 35 days apart or occur fewer than 4–9 times per year.

A variety of factors can cause irregular periods. They include:

  • stress or anxiety
  • changes in birth control method
  • hormone imbalances
  • bleeding disorders
  • benign lesions like uterine fibroids, endometrial polyps, and scarring
  • medications
  • infections in the uterus
  • cancer of the uterine lining or cervical cancer

Anyone who is concerned about irregular periods should contact a doctor.

What is amenorrhea?

Amenorrhea is when a period stops having periods altogether. This is expected during pregnancy and breastfeeding. Some people also stop having periods if they begin a hormonal method of birth control.

Many other factors can also cause periods to stop. They include:

  • stress
  • rapid weight loss
  • intense physical training
  • eating disorders
  • some medications
  • conditions that affect hormone levels, such as polycystic ovary syndrome
  • conditions or treatments that affect the function of the ovaries, such as radiation therapy

Periods do not require treatment, but home care can help a person cope with any PMS symptoms. People can try:

  • Pain medication: For period pains and discomfort, over-the-counter (OTC) pain medications can be effective. These could include acetaminophen (Tylenol), ibuprofen, or aspirin.
  • Exercise: Exercise may help reduce discomfort and pain before and during periods.
  • Relaxation techniques: These can include breathing exercises, massage, and medication. Some find yoga helpful for easing pain and stress.
  • Heat treatment: Holding a hot water bottle against the abdomen may help in reducing discomfort. Warm baths may also help, providing both relaxation and gentle heat.
  • Contraception: Hormonal contraceptives can reduce many period-related symptoms, including pain. The lining of the uterus will be thinner, resulting in less contraction during menstruation.

Pregnancy occurs if sperm from a male reaches an egg in the fallopian tube. If the sperm fertilizes the egg and successfully implants in the uterus, it can begin to grow and develop. Once this happens, a person will stop menstruating for as long as pregnancy lasts.

However, while periods do stop, many experience light bleeding or spotting during pregnancy, including around the time they might usually get a period.

Bleeding during pregnancy can happen for several reasons. It can be a sign of implantation, hormonal shifts, or sometimes, pregnancy loss. A person should consult a doctor immediately if they are pregnant and experience what seems like a period.

Generally, menstruation means a person is not in the fertile phase of their cycle and therefore cannot get pregnant yet. However, there are exceptions to this.

Sperm can live in the reproductive tract for up to 5 days. If someone ovulates early, they may survive long enough to fertilize an egg.

People can also mistake other types of vaginal bleeding for a period, such as bleeding due to a medical condition. Therefore, bleeding is not always a guarantee that someone is not in their fertile phase of the cycle.

Menstruation is when the lining of the uterus sheds, causing blood to flow from the vagina. Usually, it lasts around 3–7 days. It marks the beginning of a new menstrual cycle, which is the natural fluctuation in hormones and fertility that most females experience from puberty to menopause.

Having a period means someone is not pregnant, but that it may be possible for them to become pregnant in the future. This can happen any time around ovulation when the ovaries release an egg. Pregnancy, breastfeeding, and some medical conditions can stop ovulation, causing irregular or absent periods.

People with severe pain, bleeding, or PMS symptoms should consult a health professional for diagnosis and treatment.