New research suggests men performing oral sex are more likely to get a rare form of mouth and throat cancer.
Some types of oral cancer are linked to human papilloma virus (HPV) infection in the mouth and throat.
Oral cancers are sometimes called head and neck cancers.
The umbrella refers to cancers of the mouth, lip and tongue, as well as cancers of the tonsils, oesophagus, voice box, and thyroid gland.
Johns Hopkins researchers discovered men who have performed oral sex on five or more partners have the highest risk of HPV-related cancers.
Staggeringly, an estimated eight out of 10 British adults will be infected with the HPV virus at some point in their lives.
But the risk is understood to be lower in women who do not smoke, as well as those with fewer than five oral sex partners during their lifetime.
There are over 100 different kinds of HPV but only a few are known to cause cancer.
HPV strains 16 and 18 are already known to trigger most cervical cancer, and HPV16 causes oropharyngeal cancer.
Co-author associate professor Dr Carole Fakhry at the Johns Hopkins Department of Otolaryngology said: "Currently there are no tests that could be used for screening people for oropharyngeal cancer.
"It is a rare cancer and for most healthy people the harms of screening for it would outweigh the benefits because of the problem of false positive test results and consequent anxiety.
"Our research shows that identifying those who have oral HPV infection does not predict their future risk of cancer well, and so screening based on detecting cancer-causing oral HPV infection would be challenging.
"However, we are carrying out further research of oral HPV infection in young healthy men to explore this further.
"Other research is being done on different biological markers and it is possible some of them could be used for oropharyngeal cancer screening in the future in some people; for example, they might be useful in men but not in women given their lower cancer risk.
"Some studies suggest people who have antibodies against cancer-causing types of HPV have an increased risk of HPV-related cancer, but these antibodies are very rare.
"Therefore, it is not yet clear whether they will be useful for screening. Presently, these tests are not commercially available, and are still in research labs only."
Associate Professor Amber D'Souza, of Johns Hopkins Bloomberg School of Public Health in the US, said: "For these reasons, it would be useful to be able to identify healthy people who are most at risk of developing oropharyngeal cancer in order to inform potential screening strategies, if effective screening tests could be developed.
"Most people perform oral sex in their lives, and we found that oral infection with cancer-causing HPV was rare among women regardless of how many oral sex partners they had.
"Among men who did not smoke, cancer-causing oral HPV was rare among everyone who had less than five oral sex partners, although the chances of having oral HPV infection did increase with number of oral sexual partners, and with smoking."
If you're worried about oral cancer, see your GP.
When mouth cancer is established, it has fairly clear symptoms, and your GP should be able to see them by looking in your mouth.
If oral cancer is diagnosed early, it is easier to treat, but about half of these cancers are diagnosed when the disease has already spread within the neck.
The symptoms of oral cancer include:
- red – or red and white – patches on your tongue or the lining of your mouth
- one or more mouth ulcers that do not heal after three weeks
- a swelling in your mouth that lasts for more than three weeks
- pain when swallowing
- a feeling as though something is stuck in your throat