Causes and Risk Factors of HPV

HPV through transmission electron micrograph
Human papilloma virus.  Getty Images

There are more than 150 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. HPV can cause genital or anal warts and, in some cases, cancer (depending on the strain). But, not everyone develops symptoms of an HPV infection—either immediately or at all. This makes the spread of infection quite common.

Common Causes

Vaginal and anal intercourse are the most common means of HPV transmission, although it can be passed less commonly by oral sex. Even genital-on-genital rubbing can be enough to spread the virus. It's important that young people are informed about this, as they may be particularly unaware that sexually transmitted infections can be passed without penetration.

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.

If you have HPV, the infection will usually resolve itself without treatment within 18 to 24 months. It is during this time that you can pass the virus to others. Because HPV is often "invisible" with no outward signs, people will often be 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 have sex with men (MSM) 
  • You are transgender
  • You have HIV or another disease or condition that weakens your immune system

In addition to engaging in everyday HPV prevention strategies, you may consider speaking with your healthcare provider about the HPV vaccines CervarixGardasil, and Gardasil 9, especially if any of the above applies to you.

Low- and High-Risk Strains

While most HPV strains have the potential to cause genital warts, only around 30 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 the two low-risk strains responsible for around 90 percent of all genital warts. Genital warts caused by these strains rarely progress to cancer.
  • High-risk strains are those 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 percent of cervical cancers, while HPV 16 accounts for more than 90 percent of anal cancers. Other high-risk types include HPV 31, 33, 35, 45, 52, 58, and 59.

There is no way to tell whether a genital wart is "low-risk" or "high-risk" by appearance alone. Moreover, having a wart in no way suggests that you have or will get cancer. Only diagnostic tests can confirm your infection and related risks.

Risk Factors for Developing 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 plays a part in determining who gets cancer and who doesn't. 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. 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 the 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 co-existing factors, the absence of cancer screening is one of the greatest risks. This not only includes women who avoid routine Pap screening but men who are rarely screened for anal or genital problems.


Bzhalava, D.; Eklund, C.; and Dillner, J. "International standardization and classification of human papillomavirus types." Virology. 2015 Jan 8;476C:341-344. DOI: 10.1016/j.virol.2014.12.028.

Centers for Disease Control and Prevention. "HPV Vaccines: Vaccinating Your Preteen or Teen." Atlanta,Georgia; updated August 24, 2017.

Struyf, F.; Colau, B.; Wheeler, C. et al. "Efficacy of human papillomavirus (HPV)-16/18 AS04-adjuvanted vaccine against incident and persistent infection with non-vaccine oncogenic HPV types using an alternative multiplex type-specific PCR assay for HPV DNA: post hoc analysis from the PATRICIA randomized trial." Clin Vaccine Immunol." 2014: 22(2): 235-244. DOI: 10.1128/CVI.00457-14.