Originally published 2016-01-22.
People kiss because the habit sits where biology, bonding and culture meet. The leading scientific explanations say a kiss may have grown out of mouth-to-mouth feeding between parents and infants, that it lets two people get close enough to judge each other by smell and taste, and that it releases brain chemicals linked to pleasure and attachment. Yet romantic kissing is far from universal: in a well-known 2015 survey of cultures around the world, fewer than half showed clear evidence of it.
That mix of instinct and learned custom is what makes the question so interesting. Below is what researchers actually know, what remains a hypothesis, and which popular "kissing facts" deserve a raised eyebrow.
The short answer: three overlapping explanations
No single theory explains every kiss, and most scientists treat the ideas below as complementary rather than competing.
1. A leftover from feeding babies
The Austrian ethologist Irenäus Eibl-Eibesfeldt argued that kissing developed from premastication, sometimes called kiss-feeding: a parent chews food and passes it to a child mouth to mouth. Many birds feed chicks beak to beak, and several primates, including chimpanzees, share food this way. In human societies without commercial baby food, the practice was widespread and is still seen in some places today. If an infant learns to associate mouth contact with comfort, food and safety, it is a short step to using the same gesture as a sign of affection later in life.
2. A close-range way to size up a partner
A kiss brings two noses and two mouths closer together than almost any other social act. Smell and taste carry chemical information about health, hygiene and, some researchers suspect, aspects of the immune system. Saliva also contains small amounts of hormones such as testosterone. The idea is that early humans who enjoyed this close contact had an extra filter for choosing partners, so the liking for it spread. It is an appealing hypothesis, but it remains hard to test, and a pleasant kiss is certainly no guarantee of genetic compatibility.
3. A bonding signal, borrowed from grooming
A more recent proposal, published in 2024, suggests human kissing descends from the last stage of grooming in our ape relatives, when lips touch the fur of a companion. On this view, the kiss kept its social job, building trust and closeness, long after our ancestors lost most of their body hair. A 2025 study in Evolution and Human Behavior went further and estimated that kissing-like behaviour may have appeared in ancestral apes between roughly 21.5 and 16.9 million years ago.
What happens in the body during a kiss
Lips are among the most densely innervated areas of skin, which helps explain why a light touch there feels so intense. Kissing is linked to the release of oxytocin, often described as a bonding hormone, along with dopamine, which is tied to reward and wanting, and endorphins, which lift mood. A passionate kiss can also raise heart rate, much as any exciting moment does.
There is some evidence of wider benefits. In a small controlled experiment with married and cohabiting couples, partners who were asked to kiss more often over several weeks reported lower stress and greater relationship satisfaction, and their total cholesterol dropped compared with a control group. The study was modest in size, so it suggests a link rather than proving that kissing is a health treatment.
Popular lists often add that a kiss burns a few calories per minute. Any physical activity uses some energy, but the figure is small and poorly measured, so it is best treated as trivia, not a fitness plan.
Is romantic kissing universal? Not quite
Many people assume everyone kisses. Anthropologists William Jankowiak, Shelly Volsche and Justin Garcia tested that assumption by searching ethnographic records from cultures around the world. Their paper, published in American Anthropologist in 2015, found evidence of the romantic-sexual kiss in only 46% of the cultures in their sample. Parent-child kissing was far more common than lip-to-lip kissing between lovers.
In some communities, mouth-to-mouth kissing was described as unappealing or simply unknown, while affection was shown through other gestures, such as pressing noses or cheeks together or sniffing a partner's face. The researchers noted that romantic kissing was more often recorded in socially complex societies with clear social stratification. The result does not mean that half of humanity dislikes kissing today, since global media has spread the custom widely, but it does show that the romantic kiss is learned and shaped by culture as much as by instinct.
A very old habit: kissing in early written records
Written evidence of kissing goes back thousands of years. Sanskrit texts from the Vedic period, around 3,500 years old, contain some of the earliest descriptions of kiss-like behaviour, and for a long time scholars suggested the custom spread outwards from South Asia. Newer work on Mesopotamian clay tablets challenged that idea. A 2023 analysis by Assyriologist Troels Pank Arbøll and a colleague argued that kissing was already part of romantic intimacy in the region about 4,500 years ago, which points to many independent beginnings rather than one origin.
Love poetry from ancient Sumer and from New Kingdom Egypt also mentions kisses. The same research raised a less romantic point: close mouth contact can carry infections, and kissing may have helped some viruses, such as herpes simplex type 1, spread through ancient populations.
The scientific study of kissing even has its own name, philematology, from the Greek word for a kiss. Nineteenth-century thinkers such as Charles Darwin and the anthropologist Edward Burnett Tylor wrote about it, and modern psychologists continue to study why some kisses spark attraction and others end it.
Myths and half-truths worth retiring
- "A great kiss means you have found your genetic match." Taste and smell may influence attraction, but no study shows that an enjoyable kiss reliably identifies a compatible partner.
- "Everyone, everywhere, kisses romantically." As the 2015 survey showed, the romantic kiss was absent from the records of many cultures.
- "Kissing is completely harmless." It is low risk for most people, but saliva can pass on infections such as glandular fever (infectious mononucleosis, nicknamed the kissing disease) and cold sores. HIV transmission through kissing is considered extremely unlikely.
- "Precise statistics tell us how many minutes of life we spend kissing." Such figures circulate widely online, but they rest on rough guesses rather than solid measurement.
Practical takeaways
Whatever its evolutionary roots, a kiss today is a form of communication, and its meaning depends on the people involved and the setting. A peck on the cheek can be a greeting in one country and an intimate gesture in another. Within a relationship, how often people want to kiss varies a lot, and liking less of it is not a sign that something is wrong.
A few simple points follow from the science. Consent and comfort matter more than any theory. Good oral hygiene makes the close-range "chemistry check" more pleasant for both sides. Skip kissing when you have an active cold sore or a contagious illness, and if you have health concerns about infections, talk to a doctor. Beyond that, the research mostly confirms what people already sense: kissing is one of the oldest ways humans have found to say "I trust you, and I want to be close."
Sources: Wikipedia: Kiss (origins, history, health and disease transmission); Human Relations Area Files: Is the romantic-sexual kiss a near human universal? (Jankowiak, Volsche and Garcia, American Anthropologist, 2015); original article idea: I Heart Intelligence.
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