There’s a good chance you’ve had HPV — even if you never knew it.

Human papillomavirus, or HPV, is an extraordinarily common infection and is the most common sexually transmitted infection (STI). The CDC estimates that 85% of people will acquire the virus at some point during their lifetime.

Most HPV infections cause no symptoms and clear on their own. However, HPV becomes a problem when it doesn’t clear. Doctors call these persistent infections, and certain high-risk types can lead to cellular changes and, eventually, cancer in different areas of the body.

The first HPV vaccine introduced in the U.S. in 2006, Gardasil, protected against four types of HPV, including those responsible for most cervical cancers. Today’s HPV vaccine, Gardasil 9, protects against nine types and helps prevent more cancers than many people realize — not just cervical cancer.

The Centers for Disease Control and Prevention (CDC) estimates that HPV vaccination could prevent more than 90% of cancers caused by the virus. Yet, many adults came of age before HPV vaccination became routine. As of 2022, fewer than 1 in 4 adults ages 27 to 45 had received even one dose, and many may not realize they could still be eligible.

If you missed the HPV vaccine when you were younger, you may still have options — and if you’re a parent weighing its benefits, it’s worth understanding why HPV vaccination is recommended so early and what it could help prevent years later.

Which cancers can HPV cause?

Dr. Nikita Sijapati, a primary care physician at Houston Methodist, encourages patients to think about the HPV vaccine less as protection against an infection and more as protection against what that infection could potentially develop into.

“Certain high-risk types of HPV can cause persistent infections that eventually lead to cancer,” she says. “Gardasil helps prevent those infections, which is why I consider it a cancer-prevention vaccine. When we emphasize that connection, I think people understand its importance even better.”

Most people know HPV can cause cervical cancer. But persistent HPV infections can also lead to cancers of the vagina, vulva, penis, anus and oropharynx. The last one, oropharyngeal cancer, develops in the back of the throat, including the tonsils and base of the tongue.

Although HPV does not cause every cancer that develops in these parts of the body, it causes nearly all cervical cancers and many cancers affecting the other five areas. Altogether, the CDC estimates that HPV causes about 39,300 cancer cases each year in the U.S.

Historically, cervical cancer has received the most attention, partly because it is the only HPV-related cancer for which health experts recommend routine screening for the general population. Among men, however, the most common HPV-associated cancer is oropharyngeal cancer. The CDC estimates that roughly 13,200 cases occur in men each year, compared with about 3,200 in women.

So why aren't there more routine screening tests for HPV-related cancers?

According to Dr. Sijapati, there isn’t enough evidence yet to recommend routine screening for oropharyngeal or anal cancer in the general population. However, doctors may consider anal cancer screening for people in certain high-risk groups. Screening may include a digital anorectal exam, anal cytology or an anal HPV test. An abnormal result may require further evaluation with high-resolution anoscopy, a procedure that allows doctors to examine the anal canal more closely.

Without routine screening, some HPV-related cancers may remain undetected until they begin causing health problems, which is why prevention via the vaccine is so important.

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Why is the HPV vaccine recommended so young?

Hearing your child’s doctor recommend an HPV vaccine at age 9, 10 or 11 may catch you off guard. After all, why does a child need protection against an infection they’re unlikely to encounter for years? Dr. Sijapati understands why the timing can give some parents pause.

“When parents learn that HPV is sexually transmitted, the conversation can shift toward their child’s future sexual activity,” she says. “But I present it as part of their routine preventive care.”

Doctors recommend the vaccine early because it works best before someone encounters HPV.

“The vaccine provides the greatest benefit before you’re exposed,” Dr. Sijapati says. “That’s why we start at age 11 or 12, or even as early as 9. We want children to get the full benefit.”

Starting early can also make completing the recommended vaccination easier. Children who begin the series before age 15 have traditionally needed fewer doses than those who start later. The number of doses can depend on a person’s age, health history and current recommendations, so parents should ask their child’s doctor which schedule applies.

Still, many adolescents remain incompletely vaccinated. In 2024, about 78% of U.S. adolescents ages 13 to 17 had received at least one HPV vaccine dose, while only about 63% were up to date, according to the CDC.

The goal is to protect children long before they may encounter HPV and, ultimately, lower their risk of developing HPV-related cancer as adults.

How old is too old for the HPV vaccine?

There isn’t one answer for everyone. The CDC routinely recommends HPV vaccination during childhood and catch-up vaccination through age 26. After that, the decision becomes more individualized, according to Dr. Sijapati.

Children ages 9 to 12

Doctors routinely recommend the HPV vaccine at age 11 or 12, although children can receive it as early as age 9. As Dr. Sijapati explained, starting early allows children to receive the greatest possible benefit from the vaccine — well before they are likely to encounter HPV.

Teens and adults through age 26

If you didn’t receive the HPV vaccine as a child, you haven’t necessarily missed your opportunity. The CDC recommends catch-up vaccination through age 26 for anyone who wasn’t adequately vaccinated when they were younger.

Dr. Sijapati says some of her younger adult patients assume they have already waited too long.

“Sometimes I’ll see someone who’s 24 and has never had the HPV vaccine, and they’ll say, ‘It’s too late. I didn’t get it as a kid,’” she says. “And I tell them, ‘No, absolutely, we can catch up on it.’”

A doctor can review your vaccination record and help determine what you still need, particularly if you received one or more doses but aren’t sure whether you completed the vaccination recommended at the time.

Adults ages 27 to 45

HPV vaccination isn’t routinely recommended for every adult older than 26. However, some adults ages 27 to 45 who weren’t adequately vaccinated may still benefit after talking with their doctor.

The potential benefit generally decreases with age because adults are more likely to have encountered one or more types of HPV. But previous exposure to HPV doesn’t necessarily mean you have encountered all nine types covered by Gardasil 9. The vaccine may still protect against types you haven’t acquired, although it can’t treat an infection you already have.

“By ages 27 to 45, everybody has a different medical history and their own set of risk factors,” Dr. Sijapati says. “That’s why the conversation is very different.”

A doctor may consider factors such as your vaccination history and likelihood of future HPV exposure. For instance, a new partner at any age can create an opportunity for a new HPV infection. Someone in a long-term, monogamous relationship is less likely to acquire a new infection.

Adults older than 45

HPV vaccination is not currently recommended for adults older than 45. If you fall outside the approved age range, other preventive care, including recommended cervical cancer screening, remains important.

Age isn’t the only question that can shape the decision. Your previous vaccination history and whether you have already had HPV may matter, too.

What if you didn’t finish the HPV vaccine series?

If you started HPV vaccination years ago but never finished, you generally don’t have to start over. An interrupted series can typically continue where it left off, even if considerable time has passed.

“If someone started the HPV vaccine series but received only one of the recommended doses and still needs catch-up vaccination, we would use Gardasil 9 to help complete it,” Dr. Sijapati says.

How many additional doses you may need depends on factors including your age when you received the first dose, your health history and the vaccination guidance that applies to you.

People vaccinated years ago may also remember receiving a different HPV vaccine. Before Gardasil 9 became the only one distributed in the U.S., Gardasil protected against four HPV types and Cervarix protected against two. All three vaccines protected against HPV 16 and 18, the two high-risk types responsible for most cervical cancers.

Completing one of those earlier vaccine series doesn’t mean you must start over simply because Gardasil 9 covers additional types.

“If someone received the quadrivalent vaccine, or the bivalent vaccine that covered two types, CDC guidelines don’t say they need to go back and restart the series,” Dr. Sijapati says.

If you don’t remember which vaccine you received or how many doses you completed, ask your doctor to review your vaccination record. They can determine whether your previous vaccination is complete or whether you may need additional doses.

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Is the HPV vaccine safe?

It’s understandable to have questions about a vaccine recommended for your child or one you may be considering for yourself. Fortunately, HPV vaccines have nearly two decades of safety data behind them.

Researchers studied Gardasil 9 in clinical trials involving more than 15,000 people before the FDA licensed it in 2014. Since the first HPV vaccine arrived in 2006, ongoing monitoring by the CDC, FDA and other organizations has continued to support its safety. More than 135 million HPV vaccine doses have been distributed in the U.S.

The most common side effects are generally mild and temporary, including pain, redness or swelling where the shot was given, headache, nausea, dizziness or fatigue. Because adolescents can faint after receiving any vaccine, doctors typically ask them to remain seated or lying down for about 15 minutes afterward.

Like any vaccine or medication, Gardasil 9 can cause a serious allergic reaction in rare cases. Talk with your doctor about any severe allergies and what side effects to expect before vaccination.

The question to ask at your next appointment

You may not remember whether you received the HPV vaccine, which version you received or whether you completed the recommended doses. Your child’s vaccination record may be similarly fuzzy. Your next checkup is a good opportunity to find out.

If you’re a parent, ask whether your child is up to date with HPV vaccination. If you missed the vaccine when you were younger, ask whether catch-up vaccination is recommended or whether you could still benefit based on your age and health history.

Above all, don’t assume the opportunity has passed without asking.

“Start early and complete the recommended vaccination,” Dr. Sijapati says. “Remember, this vaccine is for both boys and girls. It can prevent an infection today that might otherwise lead to cancer later in life.”