Kisses pass bacteria—exact counts are shaky

Microorganisms are transferred during intimate kissing. In a study of 21 couples, researchers measured marker-bacteria transfer after a 10-second kiss and estimated an average of about 80 million bacteria. That is not the same as establishing that every kiss transfers 278 species. The figures “278” and “95% harmless” appear in popular retellings, but we could not locate a suitable primary study measuring those specific numbers. Kissing can also transmit pathogens, including herpes viruses and upper respiratory infections; risk depends on the organism and circumstances.