This leaflet explains the menstrual cycle and periods (menstruation). It mentions the common variations which are normal. Some common problems are also briefly discussed, such as heavy periods, painful periods, irregular periods, periods that stop and abnormal bleeding between periods.
This leaflet is part of our series on periods (menstruation)
Why do periods occur?
Females have small organs called ovaries in the lower part of their tummy (abdomen). The ovaries lie either side of the womb (uterus). The ovaries start to produce female hormones in girls around puberty which cause changes to the lining of the uterus. Every month during your period the lining of your womb is shed together with some blood.
The time between the start of one period and the start of the next is called the menstrual cycle. The average length of a menstrual cycle is 28 days. However, anything between 24 and 35 days is common. During the cycle various changes occur in your body. The changes are controlled by chemical substances which act like messengers in your body, called hormones. There are changing amounts of your female hormones at different times of your cycle. The menstrual cycle is split roughly into two halves:
The first half of your cycle is called the follicular or proliferative phase. The levels of your two main female hormones, oestrogen and progesterone, are low to start with and you shed the inner lining of your womb (endometrium). This causes your period (menstrual bleeding).
During this phase your ovaries are stimulated by other hormones. These travel to the ovary in the bloodstream from a gland near your brain, called the pituitary gland. One of these hormones causes some eggs in your ovaries to grow and develop in tiny fluid-filled cavities called follicles. The follicles produce oestrogen. Throughout the first half of your cycle the level of oestrogen in your blood rises. One function of oestrogen is to cause the lining of your womb to thicken (proliferate).
Ovulation occurs about halfway through your cycle (about 14 days after the start of your period). Ovulation is the release of an egg into your Fallopian tube from a follicle in an ovary. The egg travels along your Fallopian tube into your womb (uterus). The egg may be fertilised if you have recently had sex and there are sperm in your uterus.
The second half of the cycle is called the secretory or luteal phase. After ovulation, the follicle that released the egg makes a hormone called progesterone as well as oestrogen. Progesterone causes the lining of the uterus to swell and be ready to receive a fertilised egg. If the egg is not fertilised, the levels of progesterone and oestrogen gradually fall. When they fall to a low level, they lose their effect on your uterus. The lining of your uterus is then shed (a period) and a new cycle then begins.
Normal periods (menstruation)
Starting to have periods is part of growing up for girls. Periods usually start to occur around the same time as other changes happen to the body, such as starting to develop breasts or to grow pubic hair. The average age to start periods is 13 but it is normal to start at any time between the ages of 9 and 15. A small number of girls may start before or after this. Periods continue until the menopause which is usually around the age of 50 years.
What happens during a period?
For several days each month there is blood loss from the vagina. The amount of blood loss varies from period to period, and from woman to woman. Some women have a dark scanty loss, some have a heavier loss which is a brighter red. Sometimes clots are passed, especially if the loss is heavy. Sometimes there are small flaky fragments in with the menstrual blood. A normal amount of blood loss during each period is between 20 and 60 ml. (This is about 4 to 12 teaspoonfuls.) Bleeding can last up to eight days but five days is the average. The bleeding is usually heaviest on the first two days. Some pain in the lower tummy (abdomen) - period pain - is common and normal.
Sanitary towels or tampons?
When you have a period, you will need to use something to absorb the blood you lose. It is common for girls to use sanitary towels when periods first start. These are placed in your underwear to soak up the blood. They come in different sizes and styles. You may need a pad which is bigger or bulkier at night, or on the heavy days of your period. When it is light, a small panty liner may be enough.
Tampons, which you insert into your vagina to absorb the blood, can be more convenient. They need to be changed regularly. You can start to use tampons at any age after you start having periods. They may feel uncomfortable to start with and may take a little bit of practice to get used to. There are different sizes, so start with the smallest to get used to it. You may need to use several sizes of tampon during a period, depending on how heavy the bleeding is. A larger size may be needed in the early heavy stages, then a smaller one when bleeding becomes lighter. Some tampons come with an applicator. Other types are put in with your fingers. Some women and girls find one type easier; others prefer the other. Find the one which is easiest for you.
Sometimes you may like to mix and match - for example, using tampons for swimming but pads at other times. For very heavy periods you may even need to use both together.
An alternative to towels and tampons is a menstrual cup. This is a reusable device, about two inches long which is made from soft medical-grade silicone. It is placed in the vagina. The cup collects menstrual blood. It is folded and inserted into the vagina, then removed. It can be rinsed and reinserted up to every eight hours.
Do I have to avoid anything when I have a period?
No. Carry on as normal. If you find the periods painful, regular exercise sometimes helps. Periods are not dirty; they are a normal part of a woman's life. You can go swimming, have a bath, etc. You may prefer to use tampons if you enjoy swimming.
Other effects of the female hormones
The female hormones (oestrogen and progesterone) have other effects which you may notice apart from causing periods. For example, the texture of the mucus in your vagina changes at different times of your cycle. Your vagina tends to be drier, and the mucus thicker, in the first half of your cycle. Shortly after ovulation, when progesterone levels rise, the vaginal mucus becomes thinner, more watery and slippery. It becomes thicker again towards your next period as the progesterone level falls.
Progesterone may also cause water retention in various parts of your body. Your breasts may become slightly bigger or tender and your tummy (abdomen) may swell a little before a period. You may feel irritable before a period, which may be due to the hormone changes. To have such symptoms before a period is normal. Sometimes the symptoms prior to periods can be more severe. This is then called premenstrual syndrome or premenstrual tension. See separate leaflet called Premenstrual Syndrome for more details.
Some symptoms relating to periods
In general, if you have a change from your usual pattern that lasts for several periods, it may be abnormal. You should see a doctor if this occurs.
Heavy periods (menorrhagia)
This is common. It is difficult to measure blood loss accurately. Periods are considered heavy if they are affecting your life and causing problems. For example if you:
- Regularly experience flooding, when blood leaks on to your clothes or bedclothes.
- Are passing clots.
- Need double sanitary protection, ie pads and tampons together.
- Find your normal lifestyle is restricted because of heavy bleeding.
See your doctor if your periods change and become heavier than previously. There are various causes of heavy periods. However, in most women, the cause is unclear and there is no abnormality of the womb (uterus) or hormones. Treatment is available which can reduce heavy periods. See separate leaflet called Heavy Periods (Menorrhagia) for more details.
Painful periods (dysmenorrhoea)
It is common to experience an ache in your lower abdomen, back and tops of your legs, especially in the first few days of your period. The first two days are usually the worst. Some women have more pain than others. Painkillers or anti-inflammatory painkillers such as ibuprofen usually ease the pain if it is troublesome. See separate leaflet called Period Pain (Dysmenorrhoea) for more details.
The cause of the pain in most women is not fully understood. Sometimes conditions such as endometriosis can make period pains become worse. You should see a doctor if:
- The pain becomes gradually worse each period.
- Pain begins a day or more before the onset of bleeding.
- Pain is severe over the whole time of the period.
Bleeding at abnormal times
If you have vaginal bleeding at times apart from your expected periods, you should see a doctor. This includes if bleeding occurs after you have sex, or after the menopause. There are various causes of bleeding between periods. One common cause is called breakthrough bleeding, which is small bleeds that occur in the first few months after starting the contraceptive pill. This usually settles over a few months.
Periods which stop (amenorrhoea)
Pregnancy is the most common reason for periods to stop. However, it is not uncommon to miss the odd period for no apparent reason. However, it is unusual to miss several periods unless you are pregnant. Apart from pregnancy, other causes of periods stopping include stress, losing weight, exercising too much and hormonal problems. As a rule, it is best to see a doctor if your periods stop for at least six months without explanation. See separate leaflet called Absent or Irregular Periods for more details.
Also, you should see a doctor if your periods have not started at all by the age of 16.
The interval between periods can vary in some women. Irregular periods may indicate that you do not ovulate every month, and the balance of the female hormones may be upset. See a doctor if your periods become irregular in your younger years. However, irregular periods are often common in the few years leading up to the menopause.
Further help & information
Dr Tim Kenny
Dr Mary Harding
Dr Hannah Gronow