Not all the causes of CIN (cervical intra-epithelial neoplasia) are known. But women who smoke are about twice as likely to develop CIN as non-smokers.

There is also some research to suggest that women who take the contraceptive pill for longer than 10 years are slightly more likely to develop cervical cancer. If you are concerned about taking the pill, discuss it with your GP or family planning clinic.

The main cause of CIN is infection of the cervix with certain types of human papilloma virus (HPV). HPV is a very common infection. There are over 100 types of the virus and the commonest types can cause warts on the hands or verrucas on the feet. Some types can affect the genital area including the cervix, although not all of these types will show any symptoms (such as warts). The types of HPV that cause genital warts are not the same as the types that can lead to CIN. The types that cause genital warts are known as low-risk types.

As this virus is sexually transmitted, the possibility of contact with it increases with the number of partners a woman or her partner has had. It is more common in women who become sexually active at a young age when their cervix may be immature and more vulnerable.

HPV is so common that most sexually active women will be exposed to it at some time in their life. There is evidence that barrier methods of contraception, such as the cap or condoms, give some protection against the spread of HPV, but they will not cover all the susceptible areas. In most women, their body's own immune system will get rid of the HPV naturally without them ever knowing it was there.

Some types of HPV can make women more likely to develop CIN. These are known as high-risk types of HPV. In some women they cause changes in the cervix that show up as an abnormality during the screening tests. Very rarely, these changes can go on to develop into CIN or cervical cancer if they are left untreated. Through regular cervical screening, the changes caused by HPV can be picked up early and any treatment needed is simple and effective.

Testing for high risk types of HPV is being introduced into the NHS Cervical Screening Programme in some parts of England. You will be given information about this if your screening sample is tested.

Two vaccines have been produced to prevent infection with HPV. These are called Gardasil® and Cervarix®. It is hoped that the vaccines will prevent at least seven in ten (70%) of the most common type of cervical cancer (squamous cell). But HPV vaccination will not replace the need for regular cervical screening tests in women.

Any vaccine works best if it’s given to children before they reach puberty. Also, as the HPV virus can be passed on during sex, the vaccine is most effective if it is given to girls before they might start having sex.

The Department of Health intends to introduce HPV vaccination for girls aged 12 to 13 in autumn 2008. It is likely that this vaccination will protect against two types of HPV that can cause cervical cancer, as well as two other types that cause genital warts. There will also be a two year catch-up campaign from autumn 2009 for girls aged up to 18 years.