The menopause is part of the natural ageing process and is caused by a change in the balance of the body's sex hormones.

Oestrogen levels decrease as you reach the menopause, which causes the ovaries to stop producing an egg each month (ovulation). Oestrogen is the female sex hormone that regulates a woman's periods.

Most women experience the menopause between the ages of 45 and 55, with 51 the average age for it to occur.

Early menopause

In rare cases, some women experience the menopause before they reach 45.

Menopause before the age of 40 is known as premature ovarian failure (POF). POF can occur at any age. In many cases, there's no cause.

Not all women who experience premature menopause find their periods stop completely. A small number of women still have intermittent ovarian function, which means their ovaries will occasionally release eggs, and they may still be able to conceive.

Possible causes of POF include:

• hysterectomy (surgery to remove the ovaries or womb)
• certain types of radiotherapy or chemotherapy
• in rare cases, some infections, such as tuberculosis, mumps, malaria, varicella (the virus that causes chickenpox and shingles) and shigella (a type of bacteria that causes dysentery)
• certain medical conditions, such as enzyme deficiencies, Down's syndrome, Turner syndrome, Addison's disease and hypothyroidism (an underactive thyroid gland)