What Are HPV 16 and 18?

HPV is short for human papillomavirus, a very common virus that infects nearly everyone at some point.

There are many different strains of the virus, each identified with a number. HPV 16 and 18 are high-risk types known to significantly increase the risk of cervical, vaginal, and vulvar cancer in women, as well as penile cancer in men. The strains can also cause anal cancer and throat cancers in men and women.

More than 40 of the 150 or so types of HPV can infect the genital regions and other mucous membranes (such as the mouth and throat), but only some of these HPV types are known to cause cancer, according to the Centers for Disease Control and Prevention (CDC). That includes 13 different HPV types known to cause cervical cancer.

In most people, HPV infections are eventually cleared by the body, as the infected cells are shed naturally. In a minority of people, though, the HPV infection persists, and if the persistent HPV is type 16 or 18, there is a marked increase in the risk of developing genital, anal, or oral cancer (depending on where the infection is located).

But even in people whose HPV persists, the time from infection with a high-risk HPV type to the development of cancer is generally measured in years.

For women, such slow growth allows precancerous changes in the cervical cells, called dysplasia, to be found on screening tests known as Pap tests — or, more recently, HPV tests can detect high-risk types of HPV in the cells of the cervix.

Currently, no screening tests for HPV-related precancerous changes in other areas of the body are recommended by the CDC. But some medical societies recommend annual screening with an anal Pap test for certain adults with HIV, to screen for changes that may lead to anal cancer. You don’t need to have anal sex to have anal exposure to HPV, since the virus can spread from the genital region to the anus.

HPV Is Common, Yet Commonly Misunderstood

HPV is the most commonly diagnosed sexually transmitted disease (STD) in the United States and abroad. The CDC estimates that in 2018, about 43 million Americans had a form of HPV that can cause a sexually transmitted disease, and about 13 million Americans became newly infected that year.

HPV also causes common skin warts, which are not considered STDs.

But even though it’s very common, HPV is widely misunderstood.

"The most common misconception that my patients have when they get a positive test for high-risk HPV is that this is an STD similar to chlamydia or herpes," says Jane Oh, MD, an ob-gyn (obstetrician-gynecologist) in private practice Arlington Heights, Illinois.

While HPV is sexually transmitted, Dr. Oh says, almost everyone who has had sex will have HPV at one time or another.

"The only people who won’t have HPV are those who have never had sexual contact with anyone or someone who has had sexual contact with one partner who also has never had sexual contact with anyone else," Oh adds.

Even though HPV is common, many women will never know they’ve contracted it, since HPV-infected cells are often shed from the cervix with no intervention.

This is particularly true in women under 30 years old.

"Many times, when women acquire HPV at a young age, there is a high clearance rate, and they tend to clear it on their own without any need for procedures like colposcopies, which we used to perform a lot in the early 2000s," says Salena Zanotti, MD, an ob-gyn at the Cleveland Clinic in Avon, Ohio. "This is because our immune systems are definitely more active the younger we are."

A colposcopy is a procedure in which a magnifying instrument and bright light are used to examine the cervix.

Because of the lower risk that HPV poses for very young women, the CDC and the American College of Obstetricians and Gynecologists (ACOG) recommend that women ages 21 to 29 have a Pap test every three years, with the option to substitute a HPV test every five years in those ages 25 to 29.

If a woman has a history of normal Pap tests and doesn't have certain risk factors (such as a compromised immune system), ACOG says she should have one of the following starting at age 30 until age 65:

• A Pap test every three years
• A Pap test and HPV test together every five years
• Just an HPV test every five years

What if I Test Positive for HPV 16 or 18 of the Cervix?

Testing positive for HPV 16 or 18 doesn’t mean you’ll develop cervical cancer, but it does mean that any dysplasia found in a Pap test carries a higher risk of becoming a cancer.

Based on the results of your Pap test and HPV test, your doctor can develop a plan to either treat the dysplasia, do more testing to rule out cancer, or recommend more frequent follow-up visits to look for additional changes.

“Paps of the cervix have been tested for a long time, and we know the changes HPV causes in the cervix,” notes Dr. Zanotti — meaning that doctors can often tell which changes to the cervix pose the most immediate danger.

If you get diagnosed with HPV, and everything else tests okay, then most likely the HPV will clear on its own within one to two years, if you don't have a suppressed immune system.

If you're concerned about anal HPV infection, you may find that there isn’t any consistent guidance about potential testing. Oh notes that HPV doesn't cause the same changes in the anus as it does in the cervix, so a Pap test is not likely to be an effective test for most people.

If you’re considered to be at higher risk for anal HPV because you have HIV or another medical condition, your doctor may refer you to someone who performs anal cytology testing (also called the anal Pap test), anoscopies (using a scope to view the anus and rectum), or high-resolution anoscopies, which use a high-resolution magnifying instrument to identify abnormal cells.

For years, heavy tobacco and alcohol use were the main known risk factors for developing cancer of the oropharynx — the back of the throat, including the base of the tongue and the tonsils.

Today, HPV is the primary cause of oropharyngeal cancer around the world.

In the United States, HPV is thought to cause 70 percent of all oropharyngeal cancers, with HPV 16 the culprit in about 95 percent of these cases, according to Yale Medicine.

Both oral HPV infection and HPV-related oropharyngeal cancer are much more common among men than women. About 10 percent of American men have oral HPV, compared with 3.6 percent of women, according to the CDC.

In addition, oral HPV 16 infection is 6 times more common in men than in women ages 18 to 69, according to a report published in November 2017 in the journal Annals of Internal Medicine. The report also found the following:

• The overall prevalence of oral HPV infection was 11.5 percent in men and 3.2 percent in women.
• High-risk oral HPV infection was more prevalent among men than women, 7.3 percent compared with 1.4 percent.
• Among men who reported having two or more same-sex oral sex partners, the prevalence of high-risk oral HPV infection was 22.2 percent.
• Oral HPV prevalence was more than four times as high in men who also had genital HPV infection (19.3 percent) than in men without genital HPV (4.4 percent).

The good news is that oropharyngeal cancer caused by HPV has a much higher five-year survival rate after treatment than head and neck cancers not associated with HPV, according to Mount Sinai.

The HPV vaccine, Gardasil 9, protects against HPV 16 and 18, as well as several other cancer-causing types of HPV and the two main types that cause genital warts.

The CDC recommends that all adolescents get the HPV vaccine at age 11 or 12. It’s also recommended through age 26 for anyone who wasn’t fully vaccinated at a younger age.

The HPV vaccine is also an option for adults ages 27 to 45 who didn’t receive it earlier, in which case you should talk with your healthcare provider about whether it makes sense for you.

Zanotti notes that some parents may be hesitant to give their child the HPV vaccine because HPV is associated with sexual activity.

“I tell my patients, ‘If you vaccinated your child against measles, mumps, and rubella, they’re more likely to get HPV than they are to get rubella these days, and HPV is something that causes cancer.’ It's pretty clear-cut. If you can do something to prevent the cancer, why wouldn't you?” Zanotti says.

Zanotti adds that while more parents are getting their sons vaccinated against HPV, this still isn’t as common as vaccination in girls. “But if in the next 10 years, boys get the vaccine as often, we will see the amount of HPV going down significantly,” she predicts.

Still, Oh cautions that the HPV vaccine doesn’t do away with the need for safer sexual practices.

“Everyone needs to know that the HPV vaccine is not a foolproof method of preventing all cervical cancer,” Oh says. “We still need to protect ourselves. Use condoms, limit partners, support our immune systems, and get those Pap [tests] to prevent cervical cancer.”

Additional reporting by Quinn Phillips.