Head and neck cancer patients were once primarily older heavy smokers and drinkers. Now, the majority who are diagnosed with the disease are closer to middle age (many ages 40 to 55) and developed it not from years of tobacco or alcohol use but rather because they engaged in oral sex.

This shift has been traced to an increase in the human papillomavirus (HPV), the sexually transmitted infection that also causes cervical cancer. And oropharyngeal cancers are not the only malignancies the virus is spurring on. HPV is now likely responsible for more than 14,000 new cases of noncervical cancer in the U.S. each year.

Despite efforts to immunize more girls against HPV with the Gardasil or Cervarix vaccines—and continued debate about recommending the vaccine for boys—experts expect that number of these virus-linked cancers to continue to grow. “Based on what we have seen, in the past 10 years or so we don’t see that the numbers have started to plateau,” says Anil Chaturvedi, an investigator in the Division of Cancer Epidemiology and Genetics at the National Cancer Institute. “They’re still on the rise.”

The virus is exceedingly common. In the U.S. at least half of those who are sexually active will get HPV at some point during their lives, and most carriers manifest no obvious symptoms, so people who are infected are usually unaware that they have it—and could be transmitting it to their partners.

Most infections, including some 90 to 95 percent of cervical HPV infections, seem to clear on their own within a couple years. But for people whose infection does not go away, they face a higher risk of cancer.