Risk factors are those factors that when present raise the chance of a person getting that disease. However presence of a risk factor does not always mean a person will surely get the disease.

Different cancers have different risk factors. While some, like smoking and its risk of causing lung cancers, are avoidable lifestyle risk factors, some are unavoidable such as genetic predisposition to getting a cancer.

Human papilloma virus (HPV) infection

Squamous cell cancers are the commonest type of anal cancers. Most squamous cell anal cancers again have been found to be associated with HPV infection in the past.

HPV infections are also linked to cervical cancer. It is seen that women with a history of cervical cancer have an increased risk of anal cancer.

There are over 100 types of HPV. These are called papilloma viruses because some of them cause papillomas or warts. These viruses may cause warts in the genital and anal areas called condyloma acuminatum.

The 2 types of HPV that cause most cases of anal and genital warts are HPV 6 and HPV 11. They are called low-risk types of HPV because they tend to cause warts but not cancer.

The subtypes most likely to cause anal cancers include HPV-16, HPV 18, HPV 31, HPV 33, and HPV 45. These subtypes also cause cancers of the cervix, vagina, and vulva in women and cancer of the penis in men, and throat cancer in both women and men.

HPV is transmitted from one person to another during skin-to-skin contact especially during sexual intercourse that includes vaginal, anal intercourse and oral sex.

The risk rises with multiple sexual partners, ever having anal sex and no use of condoms.  HPV can also spread via hand to genitals contact. Condoms can provide some protection against HPV, but they do not completely prevent infection.

Presence of other cancers

Those who have had other cancers such as those of cervix, vagina, or vulva are at an increased risk of anal cancers. This is likely because these cancers are also caused by infection with HPV.

HIV infection

Those who are infected with human immunodeficiency virus (HIV) are much more likely to get anal cancer than those not infected with this virus.

Sexual promiscuity

Having multiple sex partners increases the risk of infection with HIV and HPV and in turn raises the risk of anal cancer. Anal intercourse especially the receiver also raises the risk of anal cancers in both men and women especially in those below 30 years of age.

Smoking

Smoking also increases the risk of anal cancer. Quitting smoking reduces the risk.

Reduced immunity

Those with a reduced immunity such as those who have HIV infection, are on long term corticosteroids, after an organ transplant etc. are at a greater risk of anal cancers.

Race and ethnicity

Anal cancer is more common in African-Americans than in whites. Among African Americans it is more common in men than in women. Overall the risk in women is slightly greater than in men.