American actor Michael Douglas says his throat cancer was caused by a virus he contracted by performing oral sex — a claim that a doctor called dubious.

In an interview with the British daily the Guardian that was published Monday, Douglas blamed cunnilingus for the disease he was diagnosed with in 2010.

Actor Michael Douglas arrives for at the 66th international film festival, in Cannes, southern France, last month. In a Guardian interview published Monday, Douglas blamed cunnilingus for his throat cancer, although doctors say it's hard to pinpoint a single cause.Actor Michael Douglas arrives for at the 66th international film festival, in Cannes, southern France, last month. In a Guardian interview published Monday, Douglas blamed cunnilingus for his throat cancer, although doctors say it's hard to pinpoint a single cause. (David Azia/Associated Press)

The 68-year-old Douglas has been free of cancer for more than two years after receiving extensive chemotherapy and has returned to acting.

Douglas has starred in many movies, including Basic Instinct and Fatal Attraction. He is currently appearing in an acclaimed biopic about the late flambuoyant pianist Liberace.

Douglas told the newspaper his cancer had been caused by the human papillomavirus (HPV), which he said led to cancer.

"It's a sexually transmitted disease," Douglas said of the virus.

Smoking, drinking also risk factors

Dr. Michael Brady, who specializes in sexual health as medical director of the Terrence Higgins Trust, told The Associated Press that oral sex could have contributed to Douglas's cancer but that it was difficult to pinpoint a single cause.

He pointed out that Douglas had been a smoker and a drinker, two factors that he said are the most common causes of oral cancer.

"There are often a number of factors, genetic, environmental, viral, that could be playing a role," he said.

Brady said there are hundreds of different types of HPV and that in most cases, it is not harmful. The risk is so low, he said, that he does not believe people should worry or change their sexual practices.

Doctors estimate up to about one third of mouth and throat cancers are HPV-related and that the types of HPV found in the mouth are likely to have been caused by oral sex. Still, most high-risk HPV types are linked to genital cancers.

For some oral cancers, certain sexual behaviours, like having oral sex with four or more people in your lifetime, can raise the risk, according to Britain's Department of Health. Oral cancers caused by HPV are most common in heterosexual men in their 40s and 50s.

Douglas is married to fellow actor Catherine Zeta-Jones.