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Home / Period Delay / What are the causes of irregular periods?

What are the causes of irregular periods?

Reasons behind irregular bleeding and spotting during your cycle

Irregular periods happen when your body doesn’t follow the natural rhythm of the menstrual cycle. This can look like long gaps between your periods, or bleeding that happens more often than it should.

As many as 25% of women (of reproductive age) experience menstrual irregularities. It is very common and in general, shouldn’t be a cause for concern.

Keep reading to learn what a typical period looks like and how to determine if your cycle is irregular. We’ve also included information on spotting, the causes of irregular bleeding, and ways you can regulate your menstruation.

What counts as a typical period?

A woman’s period comes in the first week of her menstrual cycle and typically lasts for 2-7 days. During this period the lining of the uterus is shed - which results in vaginal bleeding.

Normal periods can look like any of the following:

  • blood that is light pink, or brown (usually at the beginning or end of your period)
  • blood that is bright red, usually during the heaviest days of your period
  • 2-7 days of continual bleeding
  • enough blood to require menstrual products (like tampons or pads)
  • dark blood clots mixed up with bright red blood
  • roughly 1-5 tablespoons of blood lost (though bleeding can be heavier than this)
Close-up of a woman holding menstrual products

Periods usually occur every 28 days, with the first day of your period marking day 1 of a new cycle.

However, it is normal for periods to be more or less frequent than this. A regular period can range from every 21 days to every 35 days.

What counts as an irregular period?

A period is irregular when you experience either very long or short gaps between bleeds. This can happen for a variety of reasons, but is most common when girls start menstruating (during puberty) and when women finish menstruating (during menopause).

An infographic about irregular periods

Your period may be irregular if:

  • there are less than 21 days between your periods
  • there are more than 35 days between your periods
  • the length of your cycle varies every month, making it difficult to track or know when to expect your next bleed

Irregular bleeding may also be accompanied by spotting or small amounts of bloody discharge that occur when you’re in between periods.

What is spotting?

The term ‘spotting’ refers to light vaginal bleeding that occurs in between menstrual cycles. It can also be recognised as bloody discharge.

Spotting is very light bleeding - it doesn’t require menstrual products like tampons or sanitary pads. If you experience vaginal bleeding that soaks a panty liner, this wouldn’t be considered as spotting.

A small amount of blood on some white briefs

In many cases, spotting is a side effect of hormonal contraception. During the first few months of taking the combined pill, it is common to experience spotting in between withdrawal bleeds.

The mini pill (progesterone-only pill) also commonly causes spotting and irregular bleeding. However, it can also stop your period altogether.

Other causes include:

  • Pregnancy: Spotting is occasionally an early sign of pregnancy. If your period is late and you are spotting, consider taking a pregnancy test.
  • Certain medical conditions: Some conditions (like endometriosis or cervical polyps) result in spotting. Urinary tract infections (UTIs) can also cause you to bleed from the urethra, which could be mistaken for vaginal spotting.
  • Ovulation: You might experience some spotting during ovulation (when you release an egg into the womb). This type of spotting is often light pink or red.
  • Infection: Sexually transmitted infections (STIs) or infections of the cervix, vagina, or uterus can be a cause of spotting.

If you are experiencing any pain during sex that causes spotting, this might be a sign that something isn’t quite right. Consult a healthcare professional if you are consistently spotting after having intercourse.

Please note: If you frequently experience spotting and haven’t recently started hormonal contraception, consult your doctor.

What are the causes of irregular periods?

There are many possible reasons for having irregular periods. Some of the most common causes include:

Hormonal changes

When you start taking hormonal contraception like the pill, or if you have an IUD (intra-uterine device) fitted, the hormone levels in your body change.

Whilst your body adapts to these changes, it is common to experience irregular periods and ‘breakthrough bleeding’ or spotting. Spotting is even more likely if you miss a pill, or don’t take your birth control pills regularly.

Weight loss

Some women lose their period due to excessive weight loss. This is because your body isn’t able to produce the right hormones if it isn’t getting enough energy from food.

Excessive exercise

Vigorous exercise and stress can also cause your menstrual cycle to become irregular.

An infographic about the causes of irregular periods


Polycystic ovary syndrome (PCOS) is usually due to an imbalance of hormones. This means that women with PCOS can have very light or very heavy periods, with symptoms varying each month. This imbalance of hormones also causes irregular periods to occur.

Health complications

If your thyroid function is overactive your periods can become very varied. They could become very light, very heavy, or irregular.

Problems that occur in the womb can be responsible for irregular periods too. This includes uterine fibroids (a growth of harmless tumours) or polyps on the lining of the uterus.


If you are over 40, perimenopause is likely causing your periods to become less regular. Perimenopause is a woman's natural transition into menopause.


It can take a long time for your regular periods to return after childbirth if you are breastfeeding.

This is because the hormone that helps you to produce milk (called prolactin) temporarily stops you from ovulating.

However, it’s still possible to get pregnant even if you aren’t having periods. Use barrier methods of contraception to avoid an unplanned pregnancy.

How can I regulate my period?

Some women go through phases of having irregular periods which don’t require treatment. In many cases, your body's natural cycle returns by itself.

However, other women may benefit from the following if it applies to them:

  • Change your choice of birth control: Try switching to a different type of pill, with your doctor's advice.
  • Try the combined pill for PCOS: If you have PCOS, consider starting the combined pill. By stopping ovulation, you’ll no longer have a natural period. Every 4 weeks you’ll have a withdrawal bleed instead.
  • Lifestyle changes: If your period has stopped due to sudden weight loss, try to become a healthy weight again. You should do this by following a nutritious, balanced diet. Increase portion sizes and focus on good fat sources (like olives, avocados and nuts) and protein.

Should I see a doctor about irregular bleeding?

Irregular periods don’t always require help from a medical professional. However, you should visit a doctor if:

  • your periods are frequently irregular and you can’t tell why
  • you bleed for longer than 7 days on your period
  • you are experiencing weight gain, tiredness, excess hair growth, or dry/oily skin (in addition to irregular periods)
  • your periods are irregular and you’re having difficulty becoming pregnant


To sum up, most women experience irregular bleeding at some point within their lives. A lot of the time it’s unexplained - but eventually your body gets back on track.

Other reasons for irregular periods include:

  • puberty
  • perimenopause
  • new hormonal contraception
  • rapid weight loss
  • excessive exercise
  • breastfeeding
  • polycystic ovary syndrome
  • uterine or thyroid problems
Medically reviewed by Dr. Caroline Fontana Written by our editorial team Last reviewed 20-06-2024
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Further reading

How To Delay Your Period

How To Delay Your Period

Reviewed by Dr. Caroline Fontana
Understanding the menstrual cycle

Understanding the menstrual cycle

Reviewed by Dr. Caroline Fontana
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