Occasional irregularities in the menstrual cycle are not unusual and can be due to lifestyle factors and hormone fluctuations. These changes can cause periods to start and stop rapidly.

However, irregularities in the menstrual cycle can also indicate an underlying medical condition.

This article examines what can cause a period to start and stop. It also provides information on when a person should contact a doctor.

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According to the United Kingdom’s National Health Service (NHS), a period typically lasts 5 days but can range from 2–7 days. An individual’s menstrual flow is usually heaviest during the first 2 days of their period.

The menstrual cycle typically lasts between 24–38 days. It begins on the first day of a person’s period. It starts over when the next period begins.

However, the menstrual cycle can differ depending on the person, and some may experience menstrual irregularities.

Menstrual irregularities are common. Between 14–25% of people experience irregular menstrual cycles. Menstrual irregularities that can appear as if a person’s period is stopping and starting include:

  • Intermenstrual bleeding: This refers to when a person experiences bleeding between periods, also called spotting.
  • Oligomenorrhea: This term means a person experiences infrequent menstrual periods. These usually occur more than 35 days apart.
  • Polymenorrhea: A person may experience frequent menstrual periods that occur less than 21 days apart.
  • Irregular periods: A person may experience irregular menstrual periods, with the menstrual cycle having a variation of more than 20 days.
  • Shortened menstrual bleeding: Some people may have menstrual bleeding that lasts less than 2 days.

Other examples of menstrual irregularities include:

Each person will have a slightly different menstrual cycle and period. Mild variations in flow, duration, and symptoms are usually nothing to worry about.

Menstrual blood consists of blood and tissue from the lining of the uterus. This lining is the endometrium. The role of the endometrium is to receive and nourish a fertilized egg.

As the person’s cycle progresses, the endometrium grows thicker. If an egg is not fertilized, the endometrium sheds away. The menstrual blood and tissue then pass through the cervix and out of the vagina.

Sometimes, menstrual tissue can block the cervix, preventing or limiting blood and tissue from leaving the body. This blockage may create a pause in a person’s period. Once the blockage clears, the period will resume as normal.

Periods can also change from month to month due to:

  • stress
  • over exercising
  • taking certain medications
  • being unwell
  • poor nutrition
  • sudden changes in weight
  • insufficient weight
  • using hormonal birth control

Hormone levels change throughout a period, and this may affect menstrual flow.

At the beginning of a period, levels of the hormones estrogen and progesterone drop. This signals the endometrium to begin shedding and for the period to start.

Toward the end of the period, estrogen levels begin to rise again. Increasing estrogen levels cause the menstrual tissue to thicken. This hormonal change can affect the menstrual flow.

Certain medical conditions can cause hormone imbalances that may interrupt or interfere with menstruation. The following conditions may result in irregular periods:

Polycystic ovary syndrome

Polycystic ovary syndrome (PCOS) is an imbalance of hormones that affects the ovaries and ovulation.

The exact cause of PCOS is unknown. However, high levels of male hormones such as androgens and testosterone may play a role.

Females who have PCOS may experience an irregular menstrual cycle. They may also miss periods or find that their periods stop altogether.

Other symptoms of PCOS include:

Lifestyle factors can help a person manage PCOS and balance their hormone levels. Examples include:

Certain medications can also help to balance hormone levels and reduce symptoms of PCOS.


Endometriosis happens when the endometrium grows outside of the uterus.

Endometriosis may affect menstrual flow and can cause painful symptoms during periods. A person may also experience spotting between periods.

Endometriosis may occur as a result of menstrual tissue passing through the fallopian tube and into other parts of the body. Other causes may include:

Symptoms of endometriosis can include:

Over-the-counter (OTC) pain relief medication may help to relieve mild symptoms of endometriosis. Hormonal birth control may help to manage the symptoms.

Other types of hormone medication may be necessary for people who are trying to become pregnant.

In severe cases, a person may require surgery to treat their endometriosis.

Occasional irregular periods are common, particularly for adolescents who have recently had their first period.

Certain lifestyle factors, such as stress, diet, and exercise, can also affect a person’s menstrual cycle.

However, people should see a doctor or gynecologist if they notice any of the following:

  • their period frequently lasts longer than 8 days or less than 2 days
  • they do not have their period for 3 months despite not being pregnant
  • their periods are less than 21 days apart or more than 35 days apart

People should also contact a doctor if they experience any of the following symptoms:

It can be helpful for a person to keep track of their menstrual cycle and any symptoms they experience. They can then relay this information to inform the doctor’s diagnosis.

A doctor may request blood tests to check hormone levels and may also carry out a pelvic exam. If the doctor suspects an underlying health condition, they may also request an ultrasound scan of the ovaries.

The following are commonly asked questions about irregular periods.

Why does a person’s period stop and then start again?

Every person will have a slightly different menstrual cycle and period. Usually, mild variations in duration are nothing to worry about.

A person’s period may temporarily stop if menstrual tissue blocks the cervix, temporarily preventing or limiting the blood from leaving the body. Other factors, such as diet, stress, and hormonal birth control, can also affect a person’s period.

However, a person may wish to contact a doctor if they are experiencing menstrual irregularities to rule out any underlying conditions.

Is it normal for a person’s first period to start and stop?

Planned Parenthood notes that when a person first starts having a period, it can be very light or only last a few days.

Why does a person’s period stop at night and start in the morning?

A person’s period does not stop at night and start again in the morning. However, when a person with a lighter period lays down to sleep, the blood may pool in different areas of the body due to gravity and may appear to stop.

This is not true for every person, particularly those with heavy cycles.

Why is a person bleeding again after their period ended?

A person may experience irregular vaginal bleeding due to hormonal birth control, changes in hormonal levels, injury to the vagina, fibroids, vaginal dryness, and stress. It can also be a sign of an infection or cancer.

If a person is experiencing irregular vaginal bleeding, they should contact a doctor for an accurate diagnosis.

Irregular periods are not always a cause for concern. Periods that stop and then restart are often the result of normal hormone fluctuations during menstruation.

A person should see a doctor or gynecologist if these irregularities occur with every period or if they experience other symptoms.

A doctor can check hormone levels and may perform other diagnostic tests to determine the cause of irregular periods.