Oct. 29, 2015 -- Two-thirds of people worldwide -- 3.7 billion of those under age 50 -- have the virus that causes cold sores, according to the World Health Organization.
The herpes simplex 1 virus (HSV-1) can also cause sores on the genitals and the WHO said oral sex is becoming the main way the incurable virus is passed from person to person, NBC News reported.
"The global burden of HSV-1 infection is huge," WHO researchers wrote in the journal PLoS One. "An estimated 140 million people aged 15-49 years were calculated to have prevalent genital HSV-1 infection globally in 2012."
In the Americas, 49 percent of women (178 million) and 39 percent of men (142 million) have HSV-1, the lowest regional rate in the world, WHO said. The rates are 87 percent in Africa and nearly 60 percent in Southeast Asia, NBC News reported.
Another herpes virus -- HSV-2 -- is the kind most people associate with sexually transmitted infections. This study shows that two kinds of incurable herpes viruses cause large numbers of such infections.