Your risk of developing anal cancer depends on many things, including age and lifestyle factors. Having HPV is the biggest risk factor for anal cancer. Most of us have HPV at some point during our life. But for most people it won't cause anal cancer.
Anything that can increase your risk of cancer is called a risk factor. Those that lower the risk are called protective factors.
Having one or more risk factors doesn’t mean that you will definitely get anal cancer.
Human papilloma virus (HPV)
Men and women with HPV have an increased risk of developing anal cancer. Around 90 in 100 cases of anal cancer (around 90%) are linked to HPV infection.
HPV is a common infection that gets passed from one person to another by sexual contact. For most people the virus causes no harm and goes away without treatment.
Types of HPV
There are many different types of HPV, most are harmless, some cause genital warts, and others can cause cancer.
Of the different types of HPV, type 16 is the most common in anal cancer.
People who have anal intercourse may have an increased risk of anal cancer. This could be due to the increased risk of HPV infection.
Using condoms every time you have sex can lower your chances of getting HPV. But HPV can infect areas that are not covered by a condom so they don't reduce the risk completely.
There are now vaccines to prevent HPV infection. All girls and boys aged 12 or 13 in the UK are routinely offered the HPV vaccine at school.
These vaccines protect against the types of HPV that are most likely to cause cancers such as cervical and anal cancer. They don’t protect against all types of HPV.
HPV vaccination works better in people who haven’t ever had an HPV infection. As HPV is mostly passed on through sexual contact, the vaccination programme is offered at a young age when people are less likely to have had sexual experiences.
Men who are 45 or under and have sex with men are able to have the HPV vaccine on the NHS when they go to a sexual health clinic or HIV clinic.
Age and gender
Your risk of developing anal cancer increases as you get older.
Around 25 out of 100 people (around 25%) diagnosed with anal cancer each year in the UK are aged 75 and over. But as anal cancer is a rare cancer the risk is still small.
Anal cancer is more common in women than men.
Human Immunodeficiency Virus (HIV)
Having the human immunodeficiency virus (HIV) increases your risk of developing anal cancer.
Some studies have shown smoking increases the risk of anal cancer. Giving up smoking can reduce your risk of developing many cancers.
History of cervical, vaginal or vulval cancer
Some studies show that if you have had cervical, vulval or vaginal cancer you have a higher risk of developing abnormal cells in the anus or anal cancer than the general population. The risk is also higher for women with a history of abnormal cells in the cervix, vulva or vagina.
This is probably due to risk factors common to all these cancers, such as HPV infection. But we need more research to fully understand how these cancers affect anal cancer risk.
Other possible causes
Stories about potential causes are often in the media and it isn’t always clear which ideas are supported by evidence. There might be things you have heard of that we haven’t included here. This is because either there is no evidence about them or it is less clear.