Snogging many partners almost quadruples a teenager’s risk of contracting two potentially deadly infections, researchers have warned. According to a study in the British Medical Journal, kissing with tongues was a major factor in spreading the meningococcal bacteria, which can cause meningitis and septicaemia.

French kissing with at least seven partners in a fortnight increased the risk of contracting meningitis or septicaemia fourfold, researchers said.

They found that teenagers who regularly attended religious ceremonies were at less risk of contracting meningococcal disease, probably because they were less likely to snog many partners.

The team, including researchers from the Institute of Child Health in London and the Health Protection Agency, which monitors infectious diseases, took blood samples and nose and throat swabs. They also asked patients about potential risk factors for meningitis. They found that those who were students, who mixed with large numbers of young people, were at a greater risk of meningococcal infection.