Cervical screening is offered because it can help detect abnormal cell changes in the cervix (the lower part of the womb) that could potentially develop into cervical cancer.

Abnormal cells that are picked up during cervical screening often return to normal on their own, so your doctor may recommend waiting to see if they do.

However, if more significant abnormalities are detected at an early stage there is the option of having treatment to remove them before they have a chance to become cancerous.

Since the screening programme was introduced in the 1980s, the number of cervical cancer cases has decreased by about 7% each year and it's estimated that up to 4,000 cases of cervical cancer are prevented each year in the UK because of cervical screening.

What causes abnormal cell changes in the cervix?

Abnormal changes in the cells of the cervix can be caused by certain high-risk types of human papilloma virus (HPV).

HPV is the name of a family of common viruses that affect the skin and the mucus membranes (moist tissue that line parts of the body), such as those in your cervix, anus, mouth and throat.

HPV is very common and is passed on through skin-to-skin contact. It's estimated that 8 out of 10 people in the UK are infected with HPV at some point during their lifetime. For most people, the virus goes away without treatment and does not cause any harm.

However, infection with some types of HPV can cause abnormal cell growth, which can lead to cervical cancer. Other forms of HPV cause genital warts.

The high-risk types of HPV that can cause abnormalities in the cells of your cervix are transmitted through sexual contact. This includes penetrative sex as well as other types of sexual contact such as skin-to-skin contact of the genital area, or using sex toys. Because most types of HPV, including high-risk types, don't cause any symptoms, you or your partner could have the virus for months or years without knowing it.

Can HPV be prevented?

It can be very difficult to prevent HPV, which is one of the reasons cervical screening is considered to be so important.

Using a condom during sex can help reduce your risk of developing an HPV infection, but as condoms do not cover the entire genital area and are often put on after sexual contact has begun, they are no guarantee against the spread of HPV.

A vaccination offering some protection against HPV is now offered to all girls aged 12-13 as part of the NHS Childhood Vaccination Programme. This has been shown to provide effective protection against HPV for at least eight years, but it is not yet known how long protection lasts beyond this time.

Read more about the HPV vaccination.

How common are abnormal results?

For every 100 women who have cervical screening, about six will have an abnormal result.

It is very rare for cancer to be diagnosed from the results of a cervical screening test. Less than one in 1,000 test results show invasive cancer.

Are there any disadvantages of screening?

Although cervical screening can help prevent cervical cancer, there are some potential disadvantages associated with screening. These include:

• potential discomfort, embarrassment or, less commonly, pain during the screening test
• a very small chance of getting incorrect results, which could lead to abnormalities being missed or unnecessary distress and treatment
• a chance of having unnecessary treatment if the abnormalities would have corrected themselves naturally
• some treatments used to remove abnormal cells may increase your risk of giving birth prematurely (before the 37th week of pregnancy) if you get pregnant in the future

However, cervical screening is offered to women aged 25-64 in England because the potential benefits of screening are believed to outweigh these risks.

Deciding whether or not to have a screening test is your choice. To help you decide, you can also read the leaflet NHS Cervical Screening: Helping You Decide (PDF, 228kb) which you should receive with your invitation to screening.

If you don't want to be invited for screening in future, contact your GP and ask to be removed from their list of women eligible for cervical screening. If you change your mind at a later date, you can simply ask your GP to put you back on the list.