The biggest risk factor for most head and neck cancers are tobacco and alcohol use. In fact, alcohol and tobacco cause about 75 percent of head and neck cancers, according to the NCI. But the other significant risk factor is infection with the human papillomavirus (HPV), the most common sexually transmitted infection (STI) in the U.S.

HPV is a group of more than 100 types of related viruses, about 40 of which are spread through skin-to-skin contact during vaginal, oral, or anal sex. About 90 percent of men and 80 percent of women who are sexually active will be infected with HPV at some point in their lives. Most HPV infections, even those with high-risk types of HPV, go away on their own within a year or two and never cause symptoms or problems.

Approximately a dozen types of HPV are associated with cancer. In fact, 70 percent of cervical cancers and 95 percent of anal cancers are caused by HPV infection, according to the NCI. Most HPV-related cancers are linked to types HPV 16 and 18. HPV also causes some vulvar, penile, rectal, vaginal, and head and neck cancers, specifically oropharyngeal (throat) cancer. However, it takes years after becoming infected with HPV before you may develop cancer.

The oropharynx, or middle throat, includes the back of your mouth (soft palette), base of the tongue, and tonsils. According to the Centers for Disease Control and Prevention (CDC), of the roughly 16,500 cases of oropharyngeal cancer diagnosed each year, about 11,600 (70 percent) are probably caused by HPV, particularly HPV type 16. Interestingly, despite the high association with oropharyngeal cancer, HPV infection isn’t associated with other types of head and neck cancers.

According to the NCI, the most common symptoms of oropharyngeal cancer are a persistent sore throat, earaches, hoarseness, swollen lymph nodes, pain when swallowing, or unexpected weight loss. Some people with throat cancer don’t experience any symptoms.

As fewer people smoke and abuse alcohol, the overall rate of head and neck cancers is declining. That’s the good news. The bad news is that HPV-related oropharyngeal cancers are on the rise in the U.S. Most of these cancers occur in men. HPV can be transmitted to the mouth and throat via oral sex.

Although HPV is a significant risk factor for cervical, anal, and oropharyngeal cancers, only about 31,500 of all cancer cases annually are associated with HPV, according to the CDC, despite the fact that nearly 80 million people are infected with HPV.

Until recently, scientists believed there were two types of HPV 16-related head and neck cancers. These classifications are based on how the DNA of the virus replicates. Now, researchers have learned there is a third type, a hybrid of the other two, and that 75 percent of HPV-related head and neck cancers are  this type. This matters because patients with the hybrid version respond better to therapy.

It also turns out that patients with HPV-related head and neck cancers actually have better survival rates than patients with other head and neck cancers. This may be because these tumors are particularly sensitive to radiation therapy.

The Food and Drug Administration has approved Gardasil 9 for the prevention of the nine types of HPV infections most likely to cause cervical cancer. Gardasil 9 is now the only HPV vaccination available in the U.S. According to the CDC, HPV vaccines protect against HPV 16, which is associated with oropharyngeal cancer. However, while HPV vaccinations may be beneficial in helping to prevent oropharyngeal cancers, to date there aren’t rigorous studies to confirm this.

To reduce your risk of throat cancer, don’t smoke, and drink alcohol in moderation. Limit the number of sexual partners you have to reduce your risk of receiving an HPV infection (or transmitting it), and get vaccinated against HPV. Additionally, using condoms and dental dams (barriers used during oral sex) can also lower your risk of getting an HPV infection.