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.

A period typically lasts for 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.

Read on to find out more about irregular periods, what can cause them, and when to see a doctor.

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It is not unusual for a person to have irregularities in their menstrual cycle.

The menstrual cycle is typically 28 days but can vary between 21–35 days. An irregular menstrual cycle is one that is shorter or longer than usual or involves a lighter or heavier flow.

Menstrual irregularities may also involve light bleeding or “spotting” between periods.

Irregular periods are common, with 14–25% of people experiencing irregular menstrual cycles. They may also experience uncomfortable symptoms, such as menstrual cramps.

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:

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Hormone levels may affect menstrual flow.

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 provides a signal for the endometrium to begin shedding, and for the period to start.

Towards 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:

  • acne, which may be on the face, back, or chest
  • thinning hair, loss of hair, or baldness
  • excess facial hair
  • weight gain
  • difficulty losing weight
  • darker areas of skin around the neck, groin, and under the breasts
  • skin tags around the armpits or neck

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

  • losing excess weight
  • eating a healthy diet
  • taking regular exercise

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:

  • genetics
  • high estrogen levels
  • problems with the immune system

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.

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A person should talk to their doctor if they have severe cramps during their period.

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.

People should see their 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 see a doctor if they experience any of the following symptoms:

  • severe cramps or other pain during a period
  • bleeding in between periods
  • much heavier bleeding than usual, or excessive bleeding needing a change of sanitary products every hour
  • much lighter periods than usual
  • feeling lightheaded, dizzy, or nauseas during a period
  • sickness or fever when using a tampon
  • severe premenstrual symptoms, such as depression or anxiety
  • any menstrual issues that stop people from continuing their normal activities

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.

Irregular periods are not always a cause for concern. Periods that stop and the 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.