A risk factor is anything that affects your chance of getting a disease such as cancer. Different cancers have different risk factors. For example, exposing skin to strong sunlight is a risk factor for skin cancer. Smoking is a risk factor for many cancers. But risk factors don't tell us everything. Having a risk factor, or even several, does not mean that you will get the disease.

Scientists have found certain risk factors that make a man more likely to develop penile cancer. Even if a person does have one or more risk factors for penile cancer, it is impossible to know for sure how much that risk factor contributes to causing the cancer. On the other hand, some men who develop penile cancer have no known risk factors.

Circumcision

Circumcision is the removal of all (or a part) of the foreskin. This procedure is most often done in infants but it can be done later in life. Circumcision seems to protect against penile cancer when it is done shortly after birth. Men who were circumcised as babies have less than half the chance of getting penile cancer than those who were not. The reasons for this are not entirely clear, but may be related to other known risk factors. For example, men who are circumcised cannot develop a condition called phimosis. Men with phimosis have an increased risk of penile cancer (see below). Also, circumcised men seem to be less likely to be infected with HPV, even after adjusting for differences in sexual behavior.

In weighing the risks and benefits of circumcision, doctors consider the fact that penile cancer is one of the least common forms of cancer in the United States. Neither the American Academy of Pediatrics nor the Canadian Academy of Pediatrics recommends routine circumcision of newborns (for medical reasons). In the end, decisions about circumcision are highly personal and depend more on social and religious factors than on medical evidence.

Although circumcision reduces the risk of penile cancer if it is done shortly after birth, having the foreskin removed later (as an adult) does not lower this risk. Adult men can lower their risk of penile cancer by avoiding things that are known to raise the risk of penile cancer. These factors are discussed in more detail later below.

Local hygiene, phimosis, and smegma

Phimosis

In men who are not circumcised, the foreskin can sometimes become tight and difficult to retract. This condition is known as phimosis. Penile cancer is more common in men with phimosis. Since the foreskin is hard to retract, someone with phimosis may have trouble cleaning the entire penis well. This can lead to the build up of secretions, leading to smegma.

Smegma

Sometimes secretions can build up underneath the intact foreskin. If the area under the foreskin isn't cleaned well, this build up can get worse and eventually result in something called smegma. Smegma is a thick, sometimes smelly substance found under the foreskin. It is made up of oily secretions from the skin, along with dead skin cells and bacteria. Although it hasn't been proven, some experts are concerned that smegma may also contain compounds that can cause cancer. Also, some older studies have suggested a link between smegma and penile cancer. Although, smegma probably doesn't cause penile cancer by itself, it can cause the penis to become irritated and inflamed, and may make it harder to see very early cancers. Men can prevent smegma from building up simply by washing the penis with the foreskin retracted.

Human papillomavirus infection

Human papillomavirus (HPV) is a group of more than 100 related viruses. They are called papilloma viruses because some of them cause a type of growth called a papilloma. Papillomas are not cancers, and are more commonly called warts. Different HPV types cause different types of warts in various parts of the body. Some types cause common warts on the hands and feet. Other types tend to cause warts on the lips or tongue. HPV infection is found in about half of all penile cancers. Some researchers believe that infection with HPV may be a risk factor for penile cancer.

HPV is the major cause of cancer of the cervix in women and thought to be responsible for cancer of the anus in men and women. It may also be responsible for some cancers of the vagina and vulva in women as well as throat cancers (in men and women). HPV is passed from one person to another during skin-to-skin contact. HPV can be spread during sex -- including vaginal intercourse, anal intercourse, and even during oral sex. Certain factors can increase a person's risk of HPV infection, such as:

• starting to have sex at an early age
• having many sexual partners
• having sex with a partner who has had many other partners
• having unprotected sex (not using a condom)

When HPV infects the skin of the external (outer) genital organs and anal area, it often causes raised, bumpy warts. These warts are called genital warts or condyloma acuminatum. They range in size from being almost too small to see to being several inches across. HPV 6 and HPV 11 cause most cases of genital warts. Because these warts rarely turn into cancer, HPV 6 and HPV 11 are called "low-risk" types of HPV. Some other HPV types are more likely to cause cancer and so are called "high-risk." They include HPV 16 and HPV 18, which cause most cases of cervical cancer, as well as some others like HPV 33, HPV 35, and HPV 45.

Smoking

Men who smoke are 4 times more likely to develop penile cancer than those who do not smoke. Smokers who have HPV infections have an even higher risk. Smoking exposes your body to many cancer-causing chemicals. These harmful substances are inhaled into the lungs, where they are absorbed into the blood. While in the bloodstream, they can travel throughout the body to cause cancer in many different areas. Researchers believe that these substances damage the DNA of cells in the penis, which can lead to the development of penile cancer.

UV light treatment of psoriasis

Men who have a skin disease called psoriasis are sometimes treated with a drug called psoralen, followed by exposure to ultraviolet light. Men who have received this treatment have a higher rate of penile cancer.

Age

The risk of penile cancer goes up with age. Nearly two-thirds of cases of the disease are diagnosed in men over age 65.

AIDS

Men with AIDS (acquired immunodeficiency syndrome) have a higher risk of penile cancer. This higher risk seems to be related to their lowered immune response, but lifestyle factors may also play a role. In some studies, men with penile cancer who were HIV-positive were more likely to smoke and to be infected with HPV than HIV-negative men with penile cancer.