The modern version of the facial herpes virus, which causes cold sores, is thought to date back about 5,000 years, according to the authors of a recent study.

The study’s co-author explained that the facial herpes virus is usually passed from parent to child, but kissing would have given it a new way to pass from host to host.

Hugging or kissing “is not a universal human trait,” she said, pointing to the difficulty of determining when the practice began or whether it is linked to the spread of HSV-1.

Charlotte Houldcroft, also of Cambridge, further noted that a virus like herpes evolves over a much larger timescale than a virus like COVID-19.

“Facial herpes hides in its host for life and is transmitted only by oral contact, so mutations occur slowly over centuries and millennia,” she said.

“Previously, genetic data on herpes only went back to 1925,” she noted, calling for more “in-depth investigations” to understand the viruses’ evolution.

“Only genetic samples dating back hundreds or even thousands of years will allow us to understand how DNA viruses such as herpes or monkeypox, as well as our own immune system, adapt to each other,” she said.