A carving at Luxor Temple in Egypt depicting Pharaoh Ramses and Queen Nefertiti embracing. AP
The new study, published this week in the magazine Science, found that it was probably widespread even in the ancient world.
It presents evidence that "lip kissing was documented in ancient Mesopotamia and Egypt" from at least 2500 BC.
Troels Pank Arboll said he and co-author Sophie Lund Rasmussen had started examining how the spread of diseases could be affected by the introduction of the practice of kissing on the lips as a romantic expression.
Arboll is an assyriologist -- a specialist in Ancient Near East studies -- at the University of Copenhagen; Lund Rasmussen is a biologist at the University of Oxford.
They found that most recent studies cited a source from India, dated around 1500 BC, as the earliest reference to "sexual-romantic kissing".
"I knew there was earlier material from ancient Mesopotamia," Arboll, who studies cuneiform writing on ancient clay tablets as part of his work, told AFP.
Although the evidence had already been collected in the 1980s, "apparently the information was never adopted in other fields", he added.
In the thousands of ancient cuneiform texts available they found relatively few references to romantic kissing.
Nevertheless, they added, "there are clear examples illustrating that kissing was considered an ordinary part of romantic intimacy in ancient times".
The texts studied implied "that kissing was something that married couples did" but also that "the kiss was regarded as part of an unmarried person's sexual desire when in love", they wrote.
The researchers differentiated between "friendly-parental kissing" and "romantic-sexual kissing".
While the former appears to be ubiquitous across time and geography, the latter is "not culturally universal".