The number of cases of mouth cancer has risen by more than 25% in 10 years, partly caused by an increase in the average number of sexual partners, say scientists.
Around 7,700 new cases were diagnosed in 2011, with men most at risk of the disease. Other causes of the cancer include smoking, drinking and poor diet.
Many cancers in younger people are the result of the human papillomavirus (HPV), often passed on by oral sex.
The actor Michael Douglas talked about the link in June when he blamed his tongue cancer partly on oral sex.
Young women are vaccinated against the virus at 13 to protect them against cervical cancer.
Now, campaigners are calling for boys to have the vaccination as well, in order to halt the "catastrophic rise" in cancers.
Most health experts agree that it is unrealistic to expect people to change their sexual habits.
Nigel Carter, chief executive of the British Dental Health Foundation, which compiled the figures from official data, said the rise was "very worrying. There is a clear gap in public knowledge about what causes mouth cancer. Smoking and drinking to excess increase your chances of getting mouth cancer by 30 times, yet so many social smokers often light up while having a drink," he told the Times.
"Of greater concern is the rise of the human papillomavirus. It is forecast to overtake smoking as the leading cause of the disease in the next ten years."
Dr Carter added: "There's probably not a lot you can do about picking up HPV if you are sexually active.
"When it comes to prevention messages, I believe in practicality and I'm not sure it's one that's going to be implemented. Oral sex with a condom or rubber dam is not going to take off."
Mouth cancer survival rates of about 50% have not changed in decades, but if the disease is caught early patients can have a 90% change of surviving.
"Ulcers that do not heal within three weeks, red and white patches and unusual lumps or swellings in the mouth should not be ignored. Our advice is clear - if in doubt, get checked out," suggested Dr Carter.
Some experts believe that oral sex may in future cause more throat cancer than smoking in men.
Researchers examined 271 throat-tumour samples collected over 20 years ending in 2004 and found that the percentage of oral cancer linked to the human papillomavirus, or HPV, jumped to 72% from about 16%, according to a report released in the Journal of Clinical Oncology.
By 2020, the virus-linked throat tumours - which mostly affected men - will become more common than HPV-caused cervical cancer, the report found.
"The burden of cancer caused by HPV is going to shift from women to men in this decade," Maura Gillison, an oncologist at Ohio State University told Bloomberg.