About 64% of people worldwide under age 50 have HSV-1, totaling roughly 3.8 billion people. In the United States, the number is lower and has been dropping: as of the most recent national survey data, about 48% of Americans aged 14 to 49 carry the virus.
Global Prevalence
HSV-1 is one of the most common infections on the planet. The World Health Organization estimates that nearly two out of every three people under 50 are infected. Most acquired the virus during childhood through nonsexual contact, such as a kiss from a parent or sharing utensils. Once someone is infected, HSV-1 stays in the body for life, which is why prevalence climbs steadily with age.
Prevalence in the United States
The U.S. runs notably below the global average. National health survey data covering 2015 to 2016 found that 47.8% of people aged 14 to 49 tested positive for HSV-1 antibodies. That figure had been falling steadily: in 1999 to 2000, it was 59.4%, meaning prevalence dropped by more than 11 percentage points over roughly 15 years.
The decline showed up across all racial and ethnic groups tracked in the survey. Among non-Hispanic white Americans, prevalence fell from 52.4% to 36.9%. Among non-Hispanic Black Americans, it went from 68.4% to 58.8%. Among Mexican-American individuals, rates dropped from 82.0% to 71.7%. While every group saw a decrease, the gaps between groups remained substantial.
How Prevalence Changes With Age
The older you are, the more likely you are to carry HSV-1. Among U.S. teenagers aged 14 to 19, about 27% tested positive. That rose to 41.3% for people in their twenties, 54.1% for those in their thirties, and 59.7% for those in their forties. This pattern reflects the simple math of a lifelong virus: every year you live is another year of potential exposure, and infections accumulate in the population over time.
These figures only cover people up to age 49. Prevalence among older adults is likely higher still, though it isn’t captured in the same national survey.
Why U.S. Rates Are Declining
The steady drop in HSV-1 prevalence, especially among younger Americans, likely reflects changes in hygiene practices and living conditions. Smaller household sizes, less crowding, and reduced sharing of personal items mean fewer opportunities for the virus to spread during childhood. Ironically, this trend has a complication: people who reach adolescence and adulthood without HSV-1 antibodies have no immune protection against the virus. When they encounter it later through intimate contact, they can develop genital HSV-1 infections rather than the oral cold sores that are more typical of childhood acquisition.
Most People Never Get Symptoms
The majority of people who carry HSV-1 don’t know they have it. Many never develop a single cold sore or any recognizable symptom. The virus settles into nerve cells near the base of the skull and can remain dormant indefinitely. Some carriers experience occasional outbreaks, typically as cold sores on or around the lips, but these tend to become less frequent over time. Because the infection is so often invisible, standard STI panels don’t typically include HSV-1 testing unless you specifically request it or have symptoms.
HSV-1 as a Cause of Genital Herpes
HSV-1 is traditionally associated with oral herpes, but it increasingly accounts for a significant share of new genital herpes cases, particularly in younger adults. This happens through oral-to-genital contact. Genital HSV-1 infections tend to recur less often than genital infections caused by HSV-2, with many people experiencing only one or a few outbreaks total. Still, the virus can be transmitted to partners during both symptomatic and asymptomatic periods, though the risk is lower when no sores are present.