For many years, smoking and drinking were considered the dominant risk factors for cancers of the throat. But on Monday, The Guardian, a British newspaper, reported that the actor Michael Douglas believed that his throat cancer was caused by an infection acquired during oral sex, highlighting a trend that has alarmed many scientists.

Mr. Douglas, 68, had previously speculated that years of smoking and drinking played a role in his disease, and his spokesman later said that although the actor had discussed oral sex’s link to cancer, he did not say it was the cause of his own cancer. But The Guardian quoted Mr. Douglas as saying, “Without wanting to get too specific, this particular cancer is caused by HPV, which actually comes from cunnilingus.”

Indeed, in recent years scientists have documented a steep rise in throat cancers caused by a strain of HPV that can be transmitted through oral sex. The virus, human papillomavirus Type 16, also causes many cases of cervical cancer in women.

In the 1980s, only a small number of throat cancers were linked to HPV infection. Historically, patients who developed the disease were in their 70s and were heavy smokers and drinkers.