Cervical cancer risks and causes

About 2,900 women are diagnosed with cervical cancer in the UK each year. Overall, 2 out of every 100 cancers diagnosed in women (2%) are cervical cancers. But it is the most common cancer in women under 35 years old.

Around 4 million women are invited for cervical screening each year in England.  About 3 out of every 200 women screened have a high grade abnormality (1.5%). Early treatment can prevent these cervical changes developing into cancer.

Anything that increases your risk of getting a disease is called a risk factor. Different cancers have different risk factors. This page discusses the risk factors for cervical cancer. Even if you have one or more of the risk factors below, it does not mean that you will definitely get cervical cancer.

Human papilloma virus (HPV) is the major cause of the main types of cervical cancer – squamous cell cancer and adenocarcinoma. There are over 100 different types of human papilloma virus (HPV). Up to 8 out of 10 people (80%) in the UK are infected with the HPV virus at some time during their lifetime. But for most people the virus causes no harm and goes away without treatment. 

Some HPV types are called the wart virus or genital wart virus because they cause genital warts. The types of this virus that cause warts are not the same types that increase the risk of cervical cancer. But some types of HPV are considered high risk for cancer of the cervix – they include types 16 and 18. If you have persistent or frequent infections with these high risk types of HPV, you are more at risk of developing pre cancerous cervical cells or cervical cancer than people who have not had these infections.

Almost all women who get cervical cancer have had past infections with HPV. As some types of HPV are passed on from one person to another through sexual contact (including non penetrative sexual activity) this has led to women's sexual behaviour being seen as a risk factor for cervical cancer. But, on the other hand, most women infected with these viruses do NOT develop cervical cancer. So other factors must also be needed.

If men use a condom during penetrative sex, this reduces the risk of a woman becoming infected with HPV. Using condoms also reduces the chance of a woman developing pre cancerous changes in the cervix (CIN) if she has HPV infection.

Vaccines to prevent HPV infection have now been licensed for use in the European Union. All girls aged 12 or 13 in the UK are now routinely offered the HPV vaccine at school. These vaccines protect against the strains of HPV that are most likely to cause cervical cancer. But they do not protect against all strains. As it takes between 10 and 20 years for a cervical cancer to develop after HPV infection, it is still important for women to carry on with cervical cancer screening. It will take some years before the introduction of the vaccine has a major effect on reducing the number of cases of cervical cancer. The cervical screening programme is continuing as before.

A recent study looked at all the research results together and found that having both herpes and HPV infection doubled the risk of squamous cell cervical cancer. This research took account of the number of sex partners women had, as well as their use of the pill.

Another study looked at infection with HPV and chlamydia (pronounced klah-mid-ee-ah). The study found that the risk of squamous cell cancer increased by about 80% in women with both infections.

If you smoke, you are more likely to develop squamous cell cervical cancer. Researchers have found cancer causing chemicals (benzyrene) from cigarette smoke in the cervical mucus of women who smoke. They think that these chemicals damage the cervix. There are cells in the lining of the cervix called Langerhans cells that specifically help fight against disease. These cells do not work so well in smokers.

If you have a high risk type of HPV infection and smoke, you are twice as likely to have pre cancerous cells in your cervical screening test, or to get cervical cancer. The Langerhans cells are less able to fight off the virus and protect the cervical cells from the genetic changes that can lead to cancer.

Remember that if you smoke you are more likely to get cervical cancer. If you have mild pre cancerous changes in your cervical screening test, the cells are more likely to go back to normal without any treatment if you stop smoking.

If you have a weakened immune system, then your risk of many cancers, including cervical cancer, is higher than average. People with HIV and AIDS, or people taking drugs to suppress their immune systems after an organ transplant, are more at risk of developing cervical cancer if they also have HPV infection.

This is because a healthy immune system normally protects you from cells that have become abnormal. Your immune system will kill off the cells and so prevent them from becoming cancerous.

Research that looked at a number of studies together shows that taking the pill could increase a woman's risk of developing cervical cancer. It is not clear why this is. The researchers took account of other factors, such as the number of sexual partners, smoking, and most importantly, infection with HPV. Researchers suspected that there was a link with taking the pill, but clear evidence has not come out of the studies until now.

We thought that the pill was statistically linked to cervical cancer because women on the pill are more likely to be sexually active and so more at risk of picking up HPV. Also, they do not necessarily use barrier contraception (condom or cap) which could prevent them picking up the human papilloma (wart) virus. But now it seems that it may actually directly increase the risk.

About 8 in 100,000 women get cervical cancer every year in the UK. The recent research suggests that amongst women who have taken the pill for at least 5 years, that risk is doubled. But this is still a small risk, and it is important to know that taking the pill can help to protect you against womb and ovarian cancers.

The evidence suggests that the increased risk of cervical cancer begins to drop as soon as you stop taking the pill. After 10 years the risk is the same as if you had never taken it. The important thing to remember is that regular screening can pick up changes in the cervix before they develop into a cancer. Obviously, screening is now very important for women taking the pill.

Some research suggests that women with partners who have been circumcised are less likely to get cervical cancer. This may be because men who are circumcised are less likely to carry HPV infection. This research took into account different factors relating to sexual behaviour.

You will quite often hear that women who started having sex young or women who have a lot of different sex partners are more likely to get cervical cancer. But really, this is only true because the earlier you start having sex and the more men you have sex with, the more likely you are to pick up an infection with a high risk (cancer causing) human papilloma virus (HPV). And so then you are more at risk of developing cervical cancer.

It is not correct to say that women who get cervical cancer have it because they were promiscuous (slept around). After all, you could have only slept with one man and still caught the virus if he had it. If he's had lots of partners, that will increase your risk, because it indirectly exposes you to possible sexual infections from lots of other people.

A Cochrane review, published in 1999, found that health education can help women to reduce their risk of cervical cancer. Teaching women about healthy sexual behaviour helped them behave in ways that lowered their cervical cancer risk. The teaching included information about

• How to use a condom
• How to avoid sex when they are young
• How to reduce their number of sexual partners
• How to negotiate safe sex

The education helped them to protect themselves from unsafe sex and talk to their partners about their need to do this. You can read this review of promoting healthy sexual behaviour in the Cochrane Library. It was written for researchers and specialists so is not in plain English.

There is no evidence at all to say that pregnancy increases the risk of cervical cancer. Abnormalities in the cervix may become more visible during pregnancy and so be more likely to be diagnosed. Some women may have a screening test when they are pregnant. Women who are not up to date with their cervical screening are more likely to be offered a test when they go to the doctor because of their pregnancy. This screening might lead to women being diagnosed with pre cancerous changes or cervical cancer while they are pregnant. But this does not mean that the pregnancy caused the cancer – just that this is when it was picked up.

Women in developing countries have a higher cervical cancer risk. This is partly because developing countries don't have screening. It is also because women in developing countries are more likely to have large families. Women who have had 7 or more children have double the risk of women with only 1 or 2 children. Having your first baby early, before 17, also doubles the risk, compared to having your first baby at 25 or older. This research also took account of HPV infection, and found that HPV infection did not explain the increase in cervical cancer in women who had larger numbers of children. Other similar research looked at the different types of cervical cancer. They also found a doubling of risk of squamous cell cervical cancer with 3 or more children, compared to no children. But they found that the risk of adenocarcinoma went up by half (50%).

One study has shown that black women with HPV may have a lower cervical cancer risk than white women with HPV. But we need more studies to confirm any effect of ethnic group.

Another study showed that women with a first degree relative (mother, sister or daughter) diagnosed with adenocarcinoma or squamous cell carcinoma of the cervix have double the risk of developing cervical cancer, compared to women without a family history. But we don’t know whether this is linked to faulty genes, or whether it is due to common lifestyle factors. In some cases it may be that HPV infection is passed on during pregnancy and childbirth.