Some effects of the menstrual cycle can be unpleasant. Many factors can influence the length of a person’s period and how it affects their body.

This article will explore the various factors that can determine and affect the duration of the menstrual cycle.

A person can take some steps to modify their cycle and help it become more regular. However, it is usually a good idea to seek medical advice. Below, we describe when to see a doctor about irregular periods.

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A person may experience mood swings before their period arrives.

The typical length of the menstrual cycle is 28 days. Bleeding often lasts for 2–7 days.

Many factors influence the length of a person’s menstrual cycle, and some life events, including pregnancy and menopause, can pause or stop it.

During the first few years of puberty, the cycle is often irregular, but it tends to stabilize over time.

Various health issues, including those that affect the thyroid gland, can influence the menstrual cycle.

Hormones in the body fluctuate throughout the cycle, and this can cause a range of physical and emotional changes.

Premenstrual syndrome (PMS) refers to a group of symptoms that often occur before a period.

PMS may involve:

  • feeling bloated
  • having tender breasts
  • experiencing mood swings
  • feeling irritable
  • having spotty or oily skin
  • losing interest in sex

PMS can affect other health conditions. For example:

  • Depression and anxiety: PMS can make depression and anxiety worse before or during a period.
  • Irritable bowel syndrome (IBS): Before a period, symptoms of IBS, such as bloating and cramping, may be more noticeable.
  • Chronic fatigue syndrome: PMS can also exacerbate the symptoms of this syndrome.
  • Bladder pain syndrome: People with bladder pain syndrome may experience worsening PMS symptoms.

A person may find that PMS symptoms worsen in their late 30s and 40s, especially as they approach menopause.

The menstrual cycle can change over time — some become longer or lighter, for example.

These changes do not necessarily result from health issues. However, it is still a good idea to seek medical advice about any changes in periods.

Some factors that can influence the length of the menstrual cycle include:

  • Birth control pills: Contraceptive pills can help control the regularity and flow of a person’s period.
  • Smoking: According to a 2014 review, smoking can alter the effects of the relevant hormones.
  • Stress: Stress can also affect these hormone levels.
  • Weight: People with obesity have a higher risk of irregular periods.
  • Polycystic ovary syndrome (PCOS): Irregular periods are a common symptom of PCOS.
  • Endometriosis: Endometriosis can cause spotting or bleeding between periods, as well as heavy periods.
  • Pregnancy: Pregnancy pauses the cycle, though it can cause spotting that may resemble a period.
  • Menopause: The end of menstruation signals menopause.

People keep track of their periods for a variety of reasons. According to a 2017 study, the main reasons for doing so include:

  • to keep an eye on how well the body is functioning
  • to better understand the body’s reactions
  • to be prepared for periods
  • to either avoid pregnancy or help with conception
  • to gather information for a healthcare professional

A person may decide to track their period using:

  • An app: Tracking apps can help predict when bleeding will begin.
  • A calendar: Some people keep track of their periods using digital or paper calendars.
  • Birth control pills: These medications can help regulate periods, making it easier to predict when bleeding will begin.

A range of tools and strategies can help regulate periods and, in some cases, ease PMS symptoms.

Home methods

To help reduce PMS symptoms — and possibly regulate their cycle — a person can:

  • Take time to relax.
  • Exercise regularly.
  • Maintain a healthful diet.
  • Get enough sleep.
  • Stop smoking.
  • Practice yoga and breathing exercises.

Medical methods

An irregular cycle is not always a sign of a medical condition. However, if periods are irregular, very light, or very heavy, speak with a doctor.

To help regulate their menstrual cycles, many people use birth control.

Although people typically take birth control pills to prevent pregnancy, 14% of people may take them for other reasons, such as to regulate their cycles or help reduce PMS symptoms.

Anyone who notices concerning trends or changes in their periods should see a doctor.

This is especially important for people who experience severe pain or a heavy flow, which is called menorrhagia.

If a person has menorrhagia, the doctor’s initial steps may be to determine whether the person is experiencing a pregnancy loss or a health problem, such as endometriosis.

Several factors can influence the length of the menstrual cycle. Among them are stress, weight changes, smoking, and using certain medications.

Anyone who wishes to regulate their cycle may find that taking an oral contraceptive has this effect.

Usually, a doctor should investigate the cause of irregularity in a person’s menstrual cycle. They may ask the person to track their periods, using a calendar or app.

There are times when a person can expect their periods to be irregular, such as at the beginning of puberty or before menopause.

In other cases, an underlying health issue — such as PCOS or thyroid problems — may be responsible, and the person will require medical treatment.