Menstruation, or periods, is the monthly shedding of the lining of the womb.
Periods are part of the female reproductive cycle. They start during puberty (between the ages of 10 and 16) and continue until the menopause (45 to 55). The average menstrual cycle lasts 28 days, but can vary between 24 and 35 days.
It can take up to two years for periods to settle into a regular cycle. After puberty, most women develop a regular menstrual cycle, with around the same length of time between periods.
Menstrual bleeding normally lasts between two and seven days, with the average being five days.
However, some women have an irregular menstrual cycle. This is where the time between periods, the amount of blood lost and the number of days bleeding lasts all vary widely.
Why are periods sometimes irregular?
The pattern of a woman's menstrual cycle can be disturbed by a change in contraception method. It could also be affected by an imbalance of the hormones oestrogen and progesterone, which regulate the menstrual cycle. Many factors can cause a hormone imbalance (see Causes, above).
Irregular periods are common during puberty or nearing menopause. Treatment during these times is usually not necessary.
More information
For more information on periods, and specific information on heavy periods, absent periods and painful periods, see Useful links.
