Given that there is a vaccine for it, you may be surprised to learn that HPV (human papillomavirus) remains the most common sexually transmitted infection in the United States. The infection can (but does not always) cause warts on the skin and genitals. Infection with HPV raises your risk for several different kinds of cancer, including cervical, anal, penile, and head and neck (most commonly in men).

Nearly 80 million Americans, or one in four, are currently infected with HPV. An estimated 14 million people, including teenagers, become infected with it each year.

“I think one of the reasons HPV is not on people’s radars is because it doesn’t necessarily cause symptoms, like other sexually transmitted diseases might,” says Sangini S. Sheth, MD, MPH, a Yale Medicine obstetrician-gynecologist. “But HPV is responsible for the vast majority of genital warts and other precancerous and cancerous conditions. In the past year, the number of cases of oral cancer has surpassed cervical cancer in the United States and that’s related to oral sex and HPV infection.”

At Yale Medicine, a multidisciplinary group of experts are actively researching HPV infection and associated diseases. “In particular, there have been and continue to be important research studies at Yale to understand the challenges of HPV immunization and how we can improve vaccination rates,” Dr. Sheth says. “We are also investigating novel therapeutics for cervical and head and neck cancers.”

HPV gets its name from papillomas, or warts, a common symptom of some HPV infections. There are more than 100 different types of HPV, each of which is assigned a number (called the HPV type).

The various types of HPV fall into two main categories:

• Cutaneous HPV, which affects the skin. Cutaneous HPV causes common warts, not genital warts.

• Mucosal HPV, which affects cells that live on moist surfaces such as in the vagina, cervix, vulva, anus, the inner foreskin, and urethra of the penis. These types can also invade the inner lining of the nose, mouth, throat, windpipe (trachea), and passageways to the lungs (bronchi). More than 40 types of mucosal HPV are spread through direct sexual contact, including vaginal, anal, and oral sex.

Mucosal HPV is further divided into two main types based on their risk of causing cancer:

• Low-risk HPV types, which do not cause cancer but can cause skin warts on or around the genitals and anus. HPV types 6 and 11 cause 90 percent of all genital warts.

• High-risk HPV, which can cause cancer. Approximately 12 high-risk types of the virus have been identified, including types 16 and 18, which are responsible for most HPV-associated cancers.

The HPV vaccine can prevent infection, which in turn prevents certain diseases, including HPV-associated cancers. Because the dangerous forms of HPV are spread through sexual contact, people should get the vaccine before becoming sexually active to ensure its effectiveness. 

Infection with HPV does not always lead to cancer. In fact, most strains of HPV do not cause any symptoms or problems at all, but there are a dozen or so that can progress to cancer. In particular, two HPV strains (HPV types 16 and 18) cause 70 percent of all cases of cervical cancer and precancerous cervical lesions. 

And about 70 percent of head and neck, or oropharyngeal (including the tonsils, soft palate, and base of the tongue) cancers are linked to HPV.

Sexually transmitted HPV is mainly spread through direct skin-to-skin contact during vaginal, anal, or oral sex with someone who has the virus. Someone with HPV can spread the virus even when there are no apparent symptoms. HPV is not transmitted through blood or bodily fluids. 

Though not everyone gets them, the most common symptom of mucosal HPV is genital warts. It’s important to note that these typically take a while to develop, appearing weeks or months after contact with a sexual partner who has HPV, but then they can grow rapidly.

Sometimes the warts are barely noticeable, causing no discomfort. In other instances, they can cause burning pain, itching, and other uncomfortable symptoms.  

The warts start off as small, soft, moist, pink, or gray growths. They grow quickly and turn into rough, irregular bumps. They often appear in clusters and have a cauliflower-like appearance. If your warts are not uncomfortable, and are located in an area where they can’t be seen (such as in the cervix, urethra or vulva), you may not even be aware you have them.

Usually, your immune system clears an HPV infection on its own. But the infections that don’t clear are the ones that can cause cellular changes which, many years later, may turn into cancer.

“Warts are a physical growth people see—but, most of the time, the strains of HPV that cause precancerous changes or cancer go unrecognized,” Dr. Sheth says.

For women, an HPV test is typically done at the same time as a Pap smear. This is called a co-test. A sample of cells is collected from your cervix during a pelvic exam and sent to a pathologist for interpretation.

If the test is positive for HPV or the Pap shows abnormal cells that could lead to cervical cancer, your doctor may do a repeat test or perform a colposcopy (a procedure that uses a magnifying lens and light for your doctor to better see inside your cervix).

Under guidelines from the United States Preventive Services Task Force, women ages 21 to 29 should be screened every three years with a Pap test. For women ages 30 to 65, physicians may recommend getting an HPV test alone every five years, a Pap test every three years, or a co-test every five years.

There is no HPV test for men at this time. 

Though there is no treatment for HPV, the good news is that your body’s immune system will naturally heal most infections (including warts) within a few months. Most sexually active people will become infected with the virus at some point in their lives, and some may be infected multiple times. An estimated 90 percent of cases clear up within two years.

What can be treated are the cell changes that are caused by an HPV infection. A technique called cryotherapy (freezing) is often performed to remove abnormal cells in the cervix, as well as warts and other growths on other parts of the body.

Cervical cryotherapy feels something like a Pap test. It can be done in your doctor’s office without sedation. It takes about five minutes and causes minimal discomfort. If the abnormal cells have advanced to cancer, further treatment options—such as surgery, radiotherapy, and chemotherapy—may be explored.   

For penile cancer, anal cancer (which affects men and women), and head and neck cancer (which affects mostly men), surgery, chemotherapy, and radiation are treatment options. 

The World Health Organization (WHO) and Centers for Disease Control and Prevention (CDC) both recommend HPV vaccination for both sexes. When given within recommended age groups, the vaccine, which is proven to be safe and effective by the Food and Drug Administration (FDA) and the CDC, protects against diseases and cancers caused by HPV.  

Updated guidelines recommend two shots (administered six to 12 months apart) for children (boys and girls) ages 9 to 14. If the first dose of the vaccine is given after age 15, a total of three doses will be needed. While the vaccine can prevent an infection, it does not treat existing infections. In 2018, the FDA extended the age range for people to receive the vaccine from ages 9 to 26 to ages 9 to 45. 

At Yale Medicine, physicians and researchers from an array of fields spanning dermatology, pediatrics, obstetrics-gynecology, internal medicine, and oncology are active in researching HPV.

These efforts involve clinical research and educational outreach, with the goal of improving HPV vaccination rates in children. Whether it’s educating specialty physicians and parents about the benefits of the vaccine or testing for cell changes during Pap tests, Yale Medicine doctors are invested in preventing HPV infection and treating HPV-associated diseases.