A new research has revealed that oral sex dramatically increases the risk of throat and brain cancers.
The disease has traditionally been considered to be one that affects smokers and heavy drinkers in later life.
But over recent years, as cases have been rising, it has been linked with the common human papillomavirus (HPV).
It is believed oral sex may be the main way HPV – more usually associated with cervical cancer – ends up in the mouth.
The group of viruses affect the skin and moist membranes which line the body, including the anus, cervix and mouth and throat.
HPV-16 is a well-known cause of oropharyngeal tumours – those which affect the middle part of the throat including the soft palate, the base of the tongue and the tonsils.
While HPV does not directly trigger cancer, it causes changes in the cells it has infected (for example, in the throat or cervix), and these cells can then become cancerous.
Men are twice as likely to get oropharyngeal cancer as women, according to NHS choices, because performing cunnilingus is more risky than fellatio.
It is the 11th most common cancer worldwide, according to World Health Organisation figures.
Worldwide almost half-a-million patients a year will be diagnosed with oral and oropharyngeal cancer.