It’s been tenuously suggested that kissing puts people at a greater risk of getting oral cancer than smoking, with more people developing the disease due to the human papillomavirus (HPV) than those who smoke.

HPV is a common infection that is spread through skin-to-skin contact and is normally harmless. It can survive in the genitals and mouth of both men and women, and is the leading cause of cervical cancer. So does HPV really put you at a greater risk for mouth cancer than smoking?

Around eight out of 10 people will be infected with HPV at some point in their life, but that is no reason to panic. There are hundreds of different types of HPV, most of which are harmless, with only around 15 implicated in causing cancer. These are known as “high-risk” HPV types. The vast majority of the time, our immune system can deal with the virus and overcome it, but occasionally people with persistent infections of high-risk types might go on to develop cancer.

The virus causes the cancer to develop indirectly. HPV infections start in the deepest layers of the skin, causing the cells to rapidly divide so that it can make more viruses. Sometimes, in high-risk cases, the virus will damage the cells’ DNA, meaning the cells start to grow out of control and lead to cancer.

The main risk factors for developing mouth cancer are thought to be drinking alcohol and smoking, but a growing body of evidence suggests HPV might also be a significant cause. According to the NHS, around 25% of mouth and 35% of throat cancers are HPV-related, though the numbers vary. Cancer Research UK report that more than 40% of oral cancers are linked to HPV infection, a figure that is growing.

So will kissing give you cancer? Well, the CDC states that around 7% of people in the U.S. have oral HPV, and of those, around 1% have the specific high-risk type that can lead to cancer. Most cases of the infection are likely through oral sex, with straight men in their 40s and 50s the most likely to be infected. This implies that oral sex on a woman is riskier than oral sex on a man, which is thought to be linked to how much of the virus is shed by the vulva and penis, respectively.

So while HPV-related oral cancer might be on the rise, it is still incredibly rare, and it's probably not worth worrying about whether or not the next person you kiss will increase your risk.