Oral sex can spread viruses that can cause head and neck cancers, according to a new study.

The research shows a strong connection between the human papillomavirus (HPV), which can be spread through oral sex, and head and neck cancer. The virus can raise the risk of getting head and neck cancer by as much as seven times, and maybe by far more, scientists say.

But the research also shows that the virus can be detected in a mouthwash. The virus can also be prevented with a vaccine.

The study involved nearly 97,000 people in two studies, according to the researchers.

Those people first provided mouthwash samples that verified that they were cancer-free. The researchers then examined the participants over the next almost four years, and found 132 cases of head and neck cancers.

Each of those people who had head and neck cancers were compared with three people who didn’t.

The researchers found that people who had HPV-16 in their original mouthwash samples were as much as 22 times more likely to develop oropharyngeal cancer.

HPV accounts for 70 per cent of head and neck cancer, according to experts. It is so prevalent that by 2020 it is predicted to beat cervical cancer as the main cancer caused by HPV.

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Head and neck cancers were long thought to have been caused by smoking and drinking. But a sharp rise in the number of cases led doctors to speculate that there may be another cause, and the new study is the first to show conclusively that HPV-16 precedes the development of those cancers.

The explanation gained particular publicity when actor Michael Douglas said that he believed he had contracted his cancer through oral sex. The new study is proof of the strong connection between those two activities.