Causes and Risk Factors of HPV

There are more than 100 human papillomavirus (HPV) viruses, some of which are more common than others. What causes HPV, regardless of the type, is the same: sexual, skin-to-skin contact with someone who is infected.

Some strains of HPV can lead to genital or anal warts and, in some cases, cancer. Not everyone develops symptoms of an HPV infection—either immediately or at all. This makes the spread of infection quite common.

Common Causes

The most common means of HPV transmission is sexual activity, including vaginal, anal, and oral sex. 

Your risk of HPV significantly increases with your number of sex partners, although contact with just one partner who is infected can cause HPV.

While condoms provide the best means of protection short of abstinence, they can only do so if you use them consistently and correctly.

Most HPV infections (9 out of 10) go away by themselves within two years. It is during this time that you can pass the virus to others. Because HPV may not cause any symptoms, people are often unaware that they've been infected.

This further reinforces the need for condoms if you are sexually active and are not in a committed, monogamous relationship.

Doctors use numeric designations to name the various types of HPV. Since those designations are typically meaningless to non-medical professionals, physicians typically refer to a strain as being either a low-risk or high-risk HPV.

As you read on, you may feel encouraged learning that low-risk strains pose little health risk. But remember: All types of HPV are transmitted the same way.

Lifestyle and Health Risk Factors

While HPV can affect anyone, you are at increased risk if any of the following apply to you:

• You engage in/have engaged in sex with several partners
• You engage in unprotected sex or sexual contact
• You are a man who has sex with men (MSM) 
• You are transgender
• You have HIV or another disease or condition that weakens your immune system

Low- and High-Risk Strains

While most HPV strains have the potential to cause genital warts, only 13 types are associated with cancer (primarily cervical, anal, penile, and throat cancer).

Because of this, scientists have broadly classified the strains by their potential to cause cancer as follows:

• Low-risk strains are those that can cause genital warts but are otherwise harmless. HPV 6 and 11 are are responsible for around 90% of all genital warts. Genital warts caused by these strains rarely progress to cancer.
• High-risk strains are those that can cause abnormal changes in cells (dysplasia) that can lead to cancer. Depending on the HPV strain you are exposed to, the dysplasia may be mild or severe. Among the high-risk strains, HPV 16 and 18 are associated with 70% of cervical cancers. HPV 16 accounts for more than 90% of anal cancers. Other high-risk types include HPV 31, 33, 35, 45, 52, 58, and 59.

Risk Factors for HPV-Related Cancer

While certain high-risk HPV strains are associated with certain cancers, scientists are still unsure why cancer will develop in some people with HPV and not others.

It is believed that genetics and family history play a part in this. At the same time, a person's environment, lifestyle, and general health (including past infections) can also contribute.

Beyond the HPV strain and location of the infection, there are other factors that can increase a person's risk of developing cancer from HPV. Among them:

• Persistent HPV infection (lasting longer than 24 months)
• HIV co-infection (and other forms of immune suppression)
• Chlamydia and possibly herpes simplex virus infection
• Oral contraceptives (increasing cervical cancer risk)
• Having more than three full-term pregnancies (increasing cervical cancer risk)
• Anal fistula (increasing anal cancer risk)
• Being a man who has sex with men (increasing anal cancer risk)
• Cigarette smoking (impacting all cancer types)

Of all of the possible risk factors, the delaying or complete avoidance of cancer screening is among the greatest ones. This includes routine Pap smears for those born female, as well as screenings for anal or genital problems in those born male.