Almost all cases of cervical cancer are caused by the human papillomavirus (HPV).
Almost all cervical cancer cases occur in women who have been previously infected with HPV.
HPV is a group of viruses, rather than a single virus. There are more than 100 different types.
HPV is spread during sexual intercourse and other types of sexual activity, such as skin-to-skin contact of the genital areas or using sex toys, and is very common.
Most women will get some type of HPV infection at some point in their lives.
Some types of HPV do not cause any noticeable symptoms and the infection will pass without treatment.
Others can cause genital warts, although these types are not linked to an increased risk of cervical cancer.
But at least 15 types of HPV are considered high-risk for cervical cancer. The 2 highest risk are HPV 16 and HPV 18, which cause the majority of cervical cancers.
High-risk types of HPV are thought to stop the cells working normally, which can eventually cause them to reproduce uncontrollably, leading to the growth of a cancerous tumour.
As most types of HPV do not cause any symptoms, you or your partner could have the virus for months or years without knowing it.
See preventing cervical cancer for more information about reducing your chances of developing an HPV infection.
Cancer of the cervix usually takes many years to develop. Before it does, the cells in the cervix often show changes.
These cervical abnormalities are known as cervical intraepithelial neoplasia (CIN) or, less commonly, cervical glandular intraepithelial neoplasia (CGIN) depending on which cells are affected.
CIN and CGIN are pre-cancerous conditions. Pre-cancerous conditions do not pose an immediate threat to a person's health. But if they're not checked and treated, they can potentially develop into cancer.
However, even if you develop CIN or CGIN, the chances of them turning into cervical cancer are very small.
And if the changes are discovered during cervical screening, treatment is highly successful.
The progression from HPV infection to developing CIN or CGIN and then cervical cancer is very slow, often taking 10 to 20 years.
HPV infection being very common but cervical cancer relatively uncommon suggests that only a very small proportion of women are vulnerable to the effects of an HPV infection.
There appear to be additional risk factors that affect a woman's chance of developing cervical cancer.
- smoking – women who smoke are twice as likely to develop cervical cancer than those who do not smoke; this may be because of the harmful effects of chemicals found in tobacco on the cells of the cervix
- having a weakened immune system
- taking the oral contraceptive pill for more than 5 years – this risk is not well understood
- having more than 5 children, or having them at an early age (under 17 years old)
- your mother taking the hormonal drug diethylstilbestrol (DES) while pregnant with you – your GP can discuss these risks with you
The reason for the link between cervical cancer and childbirth is unclear.
One theory is that the hormonal changes that occur during pregnancy may make the cervix more vulnerable to the effects of HPV.