The rising rates of oral cancer aren't being caused by tobacco, experts say, but by HPV, the same sexually transmitted virus responsible for the vast majority of cases of cervical cancer in women.
Millions of women and girls have been vaccinated against HPV, or human papillomavirus, but doctors now say men exposed to the STD during oral sex are at risk as well and may have higher chances of developing oral cancer.
"We're looking at non-smokers who are predominantly white, upper middle class, college-educated men," Brian Hill, the executive director of the Oral Cancer Foundation, told AOL News by phone.
Tobacco use has declined over the past decade, but rates of HPV infections have risen and affect at least 50 percent of the sexually active American population, according to the Centers for Disease Control.
HPV-16, the strain of the virus that causes cervical cancer in women, has become the leading cause of oral cancer in non-smoking men, Hill said, citing research in the New England Journal of Medicine.
"When the No. 1 cause of your disease goes down [tobacco use], you would expect that the incidence of disease would go down, but that hasn't happened," he said. "In our world, this is an epidemic."
Dr. Jennifer Grandis, the vice chairwoman for research at the University of Pittsburgh and an expert on head and neck cancers, said doctors have been seeing the HPV virus in most oral cancer tumors. She said the massive push to vaccinate girls and women between the ages of 11 and 26 against HPV should have included boys and men from the beginning. Gardasil, one of the two major vaccines used to prevent HPV, wasn't approved for use in males in the United States until 2009, three years after it was approved for women.
Men have a greater chance of contracting the HPV virus from oral sex than women do from the same behavior, though researchers aren't exactly sure why. Oral cancer has a low survival rate because it is generally not discovered until it has spread to other areas, according to the CDC. Only half of people who've been diagnosed with oral cancer will live longer than five years.