Bad news for kissers: According to at least one doctor, kissing could be worse than smoking when it comes to being a risk factor for developing head and neck cancers, reports NT News.

Dr. Mahiban Thomas, head of Maxillofacial and Head and Neck Surgery at the Royal Darwin Hospital, Australia, says that there has been a "tsunami" of human papilloma virus (HPV) related cancers in his hospital, and that this trend is indicative of a growing threat worldwide.

“High-risk behaviors are oral sex, multiple kissing partners, and more recently there are reports even ‘petting’ can lead to infection,” warned Thomas. “If someone has kissed in excess of six people their risk of contracting HPV is higher, or if someone has kissed in excess of nine people the risk is significantly higher again."

HPV is actually a relatively common infection that is believed to infect around 8 out of 10 people at some point in their life. There are hundreds of different strains of HPV, however, and the vast majority of those strains do not cause cancer. Only about 15 are of the cancer-causing variety, and even these so-called "high risk" HPV types do not always cause cancer in those infected. It is most transmittable through oral sex or kissing, and is most associated with mouth, throat and cervical cancers.

Although drinking alcohol and smoking are thought to be the main risk factors for developing mouth and throat cancers, growing evidence suggests that HPV infection could be right up there too. For instance, Cancer Research UK reports that more than 40 percent of oral cancers can be linked to HPV infection, though these numbers can vary worldwide. In the U.S., as many as 70 percent of cases of oropharynx cancer (cancer in the back of the throat) are thought to be caused by one particular strain of HPV.

Dr. Thomas' claim that kissing has overtaken smoking as a risk factor for cancer may have a tad of hyperbole attached to it, but it's certainly true that HPV-related cancers appear to be on the rise, and kissing is one form of transmission. In Australia's Northern Territory, where Dr. Thomas practices, rates of head and neck cancers are well above the Australian average, and it is particularly high in ­indigenous males.

Due to the fact that HPV has long been associated with cervical cancer, it's a common misconception that only women are at threat from this virus. Actually, straight men in their 40s and 50s are the most likely to be infected due to the fact that oral sex on a woman is riskier than oral sex on a man, because the virus is shed easier by the vulva than it is by the penis.