The spread of the modern-day cold sore has been traced back to the Bronze Age kissing, according to a new study.
Research suggests the HSV-1 strain of the herpes virus arose in the wake of vast migrations of people from Eurasia to Europe around 5,000 years ago.
The migration led to larger populations, which drove up rates of transmission and new cultural practices, including kissing, according to scientists at the University of Cambridge.
They have become the first to uncover and sequence ancient genomes of the virus, which currently infects some 3.7 billion people worldwide.
Previously, genetic data for herpes only went back to 1925, but the team hunted down four samples from human remains dating over a 1,000-year period.
By comparing older samples with ones from the 20th century, they were able to develop estimates for a timeline of evolution.
Facial herpes is spread orally, and the researchers point out the earliest known record of kissing comes from a Bronze Age manuscript from South Asia.
They believe the custom may have spread westward along with migration and coincided with the spread of HSV-1.
Centuries later, the Roman Emperor Tiberius would try to ban kissing at official functions to prevent disease spreading - a move that researchers believe may have been herpes-related.
Dr Christiana Scheib, a co-senior author and research fellow at St John's College in Cambridge, said: "Every primate species has a form of herpes, so we assume it has been with us since our own species left Africa.
"However, something happened around 5,000 years ago that allowed one strain of herpes to overtake all others, possibly an increase in transmissions, which could have been linked to kissing."
Co-senior author Dr Charlotte Houldcroft, from Cambridge's Department of Genetics, added: "The world has watched Covid-19 mutate at a rapid rate over weeks and months. A virus like herpes evolves on a far grander timescale.
"Facial herpes hides in its host for life and only transmits through oral contact, so mutations occur slowly over centuries and millennia."
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