A period is the part of the menstrual cycle when a woman bleeds from her vagina for a few days. In most women this happens every 28 days or so.

It's common for women to have a cycle that occurs earlier or later than this (between 24 and 35 days).

Girls have their first period when they start puberty. This can be any age between 8 and 16, although most girls start their periods when they're about 12.

A woman's periods continue until the menopause, which usually occurs when a woman reaches her late 40s to mid-50s (the average age is 52). 

The menstrual cycle

Each menstrual cycle starts on the first day of your period (day one) and lasts until the day before your next period begins.

The reproductive organs inside a woman's body consist of:

two ovaries – where eggs are stored, developed and released

the womb (uterus) – where a fertilised egg implants and a pregnancy develops

fallopian tubes – the two narrow tubes that connect the ovaries to the womb

the cervix – the lower part of the womb that connects to the vagina

the vagina –a muscular tube leading from the cervix to outside of the body

During each menstrual cycle, levels of the hormone oestrogen rise, resulting in an egg developing and being released by the ovary (ovulation). Your womb lining thickens in preparation for a possible pregnancy.

The egg travels down the fallopian tube and if it meets a sperm and is fertilised, a pregnancy can occur.

The egg lives for about 24 hours. If it isn't fertilised, it will be absorbed into your body. The lining of your womb will come away and leave your body through the vagina mixed with blood. This is a period (it's also sometimes referred to as the menstrual flow).

Getting pregnant

Your fertile time (when you can get pregnant) can be difficult to pinpoint. It's around the time you ovulate, which for women is about 12 to 14 days before the start of the next period.

You can't get pregnant if you don't ovulate. Some hormonal methods of contraception, such as the combined pill, contraceptive patch andcontraceptive injection, work by preventing ovulation.

Body changes

Your body produces different amounts of hormones at different times during your menstrual cycle. This can cause changes in your body and your emotions.

For example, your vaginal secretions change throughout your menstrual cycle. Around the time of ovulation they become thinner and stretchy, a bit like raw egg white.

You may also have mood swings in the days before your period and your breasts may become swollen and painful.

Premenstrual syndrome (PMS) describes the physical, psychological and behavioural symptoms that can occur in the two weeks before your monthly period. It's also known as premenstrual tension (PMT).

Do you have a problem with your periods?

You may find the Health A-Z topics useful if you're concerned about your periods.

absent periods (amenorrhoea)

heavy periods (menorrhagia)

irregular periods (oligomenorrhoea)

painful periods (dysmenorrhoea)

Symptoms of periods 

During your period you'll bleed from your vagina for a few days. The bleeding will usually be the heaviest in the first two days.

How long your period lasts depends on your menstrual cycle. Your period could last for three to eight days, but it will usually last for about five.

The amount of blood you lose during your period will depend on how heavy they are. It's usually about 30 to 72 millilitres (5 to 12 teaspoons), although some women bleed more heavily than this.

If you have heavy periods, there are a number of treatment options available. If your bleeding isn't too severe, you could try using a sanitary towel or tampon with a higher absorbency.

There are also a number of medications to help reduce bleeding. For example, the levonorgestrel-releasing intrauterine system (LNG-IUS) is a small plastic device that's inserted into your womb and releases a hormone called progestogen. It prevents the womb lining growing so quickly.

Alternatively, tranexamic acid tablets work by helping the blood in your womb clot.

Before your period

The changing levels of hormones in your body before your periods can cause physical and emotional changes. For example, your breasts might get bigger, you may feel bloated or you may cry more easily.

You also may have pain or discomfort in your lower abdomen or back, which may last for some or all of your period.

If you have pain or discomfort, there are a number of self-help techniques you can try, such as using painkilling medication (paracetamol or NSAIDs), gentle exercise, applying a heat pad or hot water bottle to your tummy, and massaging your lower abdomen.

If paracetamol or NSAIDs aren't providing enough pain relief, your GP may be able to prescribe a stronger painkiller such as codeine to take as well.

Premenstrual syndrome (PMS)

Premenstrual syndrome (PMS), also known as premenstrual tension (PMT), describes the physical, psychological and emotional symptoms that can occur in the days before a woman's period. However, it doesn't affect every woman who has periods.

There are many possible symptoms of PMS. Some of the most common physical symptoms are:

fluid retention and feeling bloated

tummy pain and discomfort


changes to your skin and hair


muscle and joint pain

breast tenderness

insomnia (problems sleeping)




weight gain (up to 1kg)

Common psychological symptoms of PMS include:

mood swings

feeling upset or emotional

feeling irritable or angry

depressed mood

crying and tearfulness


difficulty concentrating

confusion and forgetfulness


decreased self-esteem

Symptoms such as fluid retention, feeling bloated, mood swings and irritability will usually improve when your period starts. They'll disappear completely a few days after your period has finished.

Some women also experience period pain (dysmenorrhoea). It's usually felt as muscle cramps in your lower tummy, which can sometimes spread to your back and thighs. The pain may come in intense spasms or it may be dull but more constant. It usually starts when the bleeding begins and lasts for 12-24 hours.

Other symptoms such as weight gain will need to be addressed with diet and exercise.

Changes in your periods

Your periods can change – for example, they may last longer or get lighter. This doesn't necessarily mean there's a problem, but it does need to be investigated. You can go to see your GP or you can visit your nearest women's clinic or contraceptive clinic.

Bleeding between periods, after having sex or after the menopauseneeds to be checked by a doctor. It might be caused by infection, abnormalities in the cervix (the neck of the womb) or, in rare cases, it could be cancer.

If you miss a period and you've had sex, you could be pregnant. Find out about taking a pregnancy test. See your GP if you're not pregnant and you've missed two or three periods.

Complications of periods 

If you have problems with your periods, talk to your GP because there may be treatments that can help.

Period problems include: 

absent periods (amenorrhoea)

heavy periods (menorrhagia)

irregular periods (oligomenorrhoea)

painful periods (dysmenorrhoea)

Absent periods (amenorrhoea)

If a woman stops having periods altogether, it's known as absent periods or amenorrhoea. It usually means that no eggs are produced. If you don't produce eggs (ovulate), you can't get pregnant.

There are many possible causes of absent periods, including severestress, extreme weight loss, various medications and polycystic ovary syndrome (PCOS). Treating the underlying cause will often lead to your periods resuming.

Heavy periods (menorrhagia)

The amount of blood lost during a period varies from woman to woman.

However, see your GP if your periods are so heavy that they're disrupting your life and making you feel miserable. There is treatment that can help.

You might have heavy periods if:

you're using many tampons or sanitary towels

blood leaks through to your clothes

you need to use a sanitary towel and a tampon to prevent leaking

Irregular periods (oligomenorrhoea)

Periods can last between two and eight days and the menstrual cycle (the time from the start of one period to the day before the next one) usually lasts 24 to 35 days.

If you have irregular periods, also known as oligomenorrhoea, the gaps between your periods will vary, as will the amount of blood you lose and how long your period lasts.

There are many possible causes of irregular periods, and treatment will depend on the underlying cause. Possible treatments include changing your method of contraception, relaxation and counselling.

Painful periods (dysmenorrhoea)

Most women experience painful periods at some point in their lifetime. The pain can be in your lower abdomen (tummy), pelvis, lower back, thighs and vagina shortly before and during your period.

The pain can vary from mild to very severe. Speak to your GP if the pain is severe and you're finding it difficult to cope.

Painkillers such as non-steroidal anti-inflammatory drugs (NSAIDs) can be used to treat painful periods.