Human papillomavirus (HPV) is a group of more than 200 related viruses that infect the skin and mucous membranes. It is the most common sexually transmitted infection in the United States, where roughly 42.5 million people carry at least one disease-associated HPV type and about 13 million acquire a new infection each year. Most infections cause no symptoms and resolve on their own, but certain strains can lead to genital warts or cancer.
How HPV Spreads
HPV passes from person to person through direct skin-to-skin contact, most commonly during vaginal, anal, or oral sex. Penetrative intercourse isn’t required; close genital skin contact during sex is enough. A person can transmit the virus even when they have no visible warts or any other signs of infection, which is one reason it spreads so easily. Because the virus can be present without symptoms for months or years, it’s often impossible to pinpoint when or from whom someone contracted it.
How Common It Is
HPV is remarkably widespread. Among Americans aged 15 to 59, about 40% are infected with at least one HPV type at any given time, which translates to roughly 77 million people. The lifetime risk of encountering the virus is even higher: most sexually active people will be infected with at least one strain at some point. These numbers include both harmless strains and those linked to disease.
High-Risk vs. Low-Risk Strains
Not all HPV types behave the same way. Scientists divide them into two broad categories based on what they can do in the body.
Low-risk strains rarely cause cancer. Their most visible effect is warts: small, flesh-colored bumps that can appear on or around the genitals, anus, mouth, or throat. Types 6 and 11 are responsible for the vast majority of genital warts. In rare cases, low-risk strains cause a condition called respiratory papillomatosis, where warts grow inside the airway and interfere with breathing.
High-risk strains can trigger cancer if the infection persists for years. There are 12 high-risk types, and two of them, types 16 and 18, are responsible for most HPV-related cancers. These strains don’t cause visible warts. Instead, they can silently alter the DNA of infected cells over time, eventually driving them toward uncontrolled growth.
Cancers Linked to HPV
Cervical cancer is the most well-known consequence of a persistent high-risk HPV infection, but it is not the only one. HPV also causes cancers of the anus, the back of the throat (oropharynx), the vulva, the vagina, and the penis. Oropharyngeal cancers linked to HPV have been rising steadily in recent decades, particularly among men. In all of these cancer types, the progression from infection to disease typically takes years or even decades, which is why regular screening matters so much for catching precancerous changes early.
What Happens After Infection
The good news is that the immune system clears the vast majority of HPV infections without any treatment. About 80% to 90% of infections resolve on their own within two years of first being detected. During this time, most people never know they were infected.
The remaining 10% to 20% of infections persist, and this is where the risk climbs. Several factors make persistence more likely: smoking, having multiple sexual partners, coinfection with other sexually transmitted infections like herpes or chlamydia, and long-term use of oral contraceptives. Age also plays a significant role. Younger women have a much higher chance of clearing the virus naturally, and with every additional five years of age, the odds of regression drop by about 20%. A persistent high-risk infection doesn’t guarantee cancer, but it is a necessary precondition for HPV-related cancers to develop.
Symptoms to Watch For
Most HPV infections produce no symptoms at all. When symptoms do appear, they typically take the form of genital warts, which can show up weeks, months, or even longer after exposure. Warts may be flat or raised, single or clustered, and can appear on the vulva, vagina, cervix, penis, scrotum, or around the anus.
High-risk HPV infections that lead toward cancer generally produce no symptoms in their early stages. Cervical precancer, for instance, is virtually always silent. That is why screening, rather than waiting for symptoms, is the primary strategy for catching these changes before they progress.
Screening and Testing
Cervical cancer screening is the main clinical tool for detecting high-risk HPV before it causes harm. The U.S. Preventive Services Task Force recommends two approaches depending on age:
- Ages 21 to 29: A Pap test (cervical cytology) every three years. HPV testing alone isn’t recommended in this age range because transient HPV infections are so common in younger adults that positive results often lead to unnecessary follow-up procedures.
- Ages 30 to 65: A Pap test every three years, a high-risk HPV test alone every five years, or both tests together every five years. HPV testing is more sensitive than cytology alone at detecting precancerous changes, though it does result in more follow-up procedures for each case found.
For men, no HPV test has been approved by the FDA, and routine HPV screening is not recommended. This is partly because there’s no reliable sampling method equivalent to a cervical swab and partly because male HPV infections are extremely common and usually clear without intervention. Men who develop anal or throat symptoms are evaluated individually.
The HPV Vaccine
Vaccination is the most effective way to prevent HPV-related disease. The current vaccine, Gardasil 9, protects against nine HPV types: the seven high-risk types that cause the majority of HPV-related cancers (16, 18, 31, 33, 45, 52, and 58) and the two low-risk types responsible for most genital warts (6 and 11).
The dosing schedule depends on when vaccination begins. Children and teens who start between ages 9 and 14 need only two doses, spaced six to twelve months apart. Those who start at age 15 or older, or who have a weakened immune system, receive three doses over six months. The vaccine works best when given before any exposure to the virus, which is why it’s routinely recommended starting at age 11 or 12. However, it can be given to anyone through age 45.
The vaccine does not treat existing infections or diseases caused by HPV types you’ve already encountered. But because most people haven’t been exposed to all nine types covered, vaccination still offers meaningful protection even for adults who are already sexually active.