US scientists say there's strong evidence linking oral sex to cancer, and have urged more study of how human papillomaviruses may be to blame for a rise in oral cancer among white men.

In the United States, oral cancer due to HPV infection is now more common than oral cancer from tobacco use, which remains the leading cause of such cancers in the rest of the world.

Researchers have found a 225 per cent increase in oral cancer cases in the United States from 1974 to 2007, mainly among white men, Maura Gillison of Ohio State University said on Sunday.

"When you compare people who have an oral infection or not ... the single greatest factor is the number of partners on whom the person has performed oral sex," said Gillison, who has been researching HPV and cancer for 15 years.

"When the number of partners increases, the risk increases," she told reporters at the American Association for the Advancement of Science meeting in Washington.