Many anal cancers are linked to lifestyle or other risk factors. Having these risk factors does not mean that you will definitely develop cancer.
Human papilloma virus (HPV)
Men and women with HPV have an increased risk of developing anal cancer. Around 9 in 10 cases of anal cancer (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.
If you have a history of genital warts you have an increased risk of anal cancer.
People who have anal intercourse or who have a greater number of sexual partners may also 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.
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.
Some studies have shown smoking increases the risk of anal cancer. Giving up smoking can reduce your risk of developing many cancers.
Having a weakened immune system
Your immune system fights infection and diseases. If you have a weakened immune system, you are at greater risk of developing anal cancer compared to the general population.
You have an increased risk if you have Human Immunodeficiency Virus (HIV). Anal cancer is generally diagnosed at a younger age among people with HIV. This is even taking into account that HIV is more common in younger people.
People taking medicines to damp down their immune system after an organ transplant (for example, a kidney transplant) also have an increased risk of anal cancer.
Your risk of developing anal cancer increases as you get older. But the risk is still small because anal cancer is a rare cancer. Around half (51%) of anal cancer cases in the UK each year are diagnosed in people aged 65 and over.
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.