For his Christmas podcast, Professor Luke dives into one of the oldest, strangest and most delightful human behaviours: kissing. And yes, there really are scientists who study it. Kissologists? Why not. Someone has to keep the flame of enquiry burning under the mistletoe. 

Kissing isn’t new. In fact, our primate ancestors may have been at it 21 million years ago. Humans, chimpanzees, bonobos and orangutans all kiss, and the trail of evolution suggests the ancient snog goes back to a shared forebear long before Christmas was invented. 

So why do we do it? Luke’s answer brings joy to his immunologist’s heart: kissing is fundamentally about the immune system. It’s bonding, soothing, socially rewarding… but it’s also a biological exchange of information. When we kiss, we taste another person’s immune profile through their saliva. We’re wired to choose partners whose immune systems are similar enough to blend but different enough to give our potential offspring an advantage — the Goldilocks zone of mate selection. 

Kissing is also bound up in how humans live. We’re pack animals; our wellbeing depends on social closeness. For parents, early kissing and mouth-to-mouth feeding once helped babies survive. For adults, it floods the brain with oxytocin — the same hormone released during breastfeeding — building trust, comfort and connection. 

And yes, kissing is… messy. Saliva production surges to dissolve bacteria. Mouth microbes are swapped. Germs hitch a lift. Glandular fever is the classic “kissing disease,” especially among teenagers, and herpes simplex moves easily through saliva. The upside? Some research shows kissing can reduce allergic reactions — including a study where hives became less severe after a 30-minute smooch. 

The benefits stack up: reduced stress, better bonding, endorphin release, raised heart rate, improved mood, and even potential perks for your complexion. A deep kiss works 24 facial muscles, stimulates circulation and boosts collagen. Science says the Christmas kiss might be good for your skin as well as your soul.