Causes and risk factors of anal cancer

In the UK, about 1,200 people develop anal cancer each year. It is slightly more common in women than men.

Anal cancer has different risk factors. Having one or more of these risk factors does not mean you will definitely get anal cancer.

Most anal cancers are caused by the human papilloma virus (HPV). Almost everyone will have HPV at some point. But not everyone will develop anal cancer.

Human papilloma virus (HPV)

HPV is a virus that is linked to different cancers, including anal cancer. It is a common infection that’s passed on through sexual contact. Most people have HPV at some point and never know they have had it.

There are over 100 types of HPV. Some types are more likely to cause cancer than others. Some types may cause genital warts. Using a condom can help reduce the risk of getting HPV.

Usually our immune system gets rid of the HPV infection without it causing any problems. But a small number of HPV infections may lead to developing a cancer.

We have more information about HPV and cancer.

Lowered immunity

The immune system is part of the body’s defence against infections. Anal cancer is more common in people who have a lower immunity. This includes:

  • people with HIV
  • people taking medicines to suppress their immune system after an organ transplant.

Sexual activity

Having lots of sexual partners increases the chance of getting HPV. But even a person with only one partner can have this virus.

Having anal sex increases the risk of anal cancer. But HPV is passed on easily through sexual contact. So people may develop anal cancer even if they have never had anal sex.


Smoking tobacco increases the risk of developing anal cancer. If you are diagnosed with anal cancer, stopping smoking has lots of benefits. Your doctor or nurse will talk to you about this. 


Like most types of cancer, the risk of developing anal cancer increases as you get older.

Anal intraepithelial neoplasia (AIN)

This is when abnormal cells develop in the skin just inside or outside the anus. This is usually caused by HPV.

Most people who have AIN have no symptoms. But symptoms can include:

  • skin changes around the anus
  • itching
  • pain
  • bleeding (but this is rare).

If AIN is left untreated, it can develop into anal cancer over many years.

Other cancers linked with HPV

HPV infection can also cause changes in the cells of the cervix or vulva. Women have a higher risk of anal cancer if they have had:

  • abnormal cells in the cervix or vulva
  • cancer of the cervix or vulva.

Back to Potential causes of anal cancer

Low immunity

People with low immunity are more likely to develop some types of cancer.

Human papilloma virus (HPV)

Human papilloma virus (or HPV) is a common infection. Some types of HPV can increase the risk of developing cancer.