A new study has found a striking link between herpes simplex virus type 1 (HSV-1)—best known for causing cold sores—and a significantly higher risk of developing Alzheimer’s disease. But there’s some promising news: people who received antiviral treatment for the virus had a notably lower risk of the neurodegenerative condition.
Alzheimer’s, which affects memory, cognition, and behavior, accounts for as much as 80% of dementia cases. While the disease’s exact cause remains unclear, this research adds to growing evidence that viral infections may play a larger role than previously thought.
Published in BMJ Open, the study analyzed data from IQVIA PharMetrics Plus, a large U.S. health insurance claims database covering 2006 to 2021. Researchers matched 344,628 individuals diagnosed with Alzheimer’s with a control group of people without neurological issues, adjusting for factors like age, gender, region, and healthcare usage.
Among those with Alzheimer’s, 65% were women, and the average age was 73. Compared to the control group, they also had a higher rate of other chronic health issues. In terms of HSV-1 exposure, the gap was clear: 0.44% of Alzheimer’s patients had a documented HSV-1 infection, versus 0.25% of those without the disease.
After adjusting for confounding factors, researchers found that individuals with symptomatic HSV-1 infections were 80% more likely to develop Alzheimer’s. Among those with HSV-1, patients receiving antiviral treatment had a 17% lower risk than those without.
Researchers also explored other common herpes viruses, including HSV-2 (which typically causes genital herpes) and varicella-zoster virus (responsible for chickenpox and shingles). These, too, were associated with a potential increase in Alzheimer’s risk, although more research is needed.
How a Cold Sore Virus May Harm the Brain
The biological link between HSV-1 and Alzheimer’s isn’t fully understood, but the leading theory centers on inflammation. HSV-1 is known to trigger immune responses in the brain, which could set off a chain reaction leading to the formation of amyloid beta, a protein that accumulates in the brains of Alzheimer’s patients.
Interestingly, amyloid beta also has antimicrobial properties. Researchers suggest the protein may form as a defense mechanism against viruses, trapping pathogens like HSV-1, but at the cost of long-term damage to brain cells.
HSV-1 DNA has been found in the amyloid plaques that characterize Alzheimer’s brains. People who carry the APOE ε4 gene, the strongest known genetic risk factor for Alzheimer’s, also appear to be more vulnerable to HSV-1 infections, adding weight to the viral theory.
The Bigger Picture
More than 35 million people around the world live with dementia, and nearly 8 million new cases are diagnosed each year. Alzheimer’s not only affects individuals and families—it carries a staggering global cost, estimated at over $300 billion in 2020.
While the new study is observational and doesn’t prove a direct cause-and-effect relationship, the findings underscore the potential of antiviral medications as a tool in dementia prevention. The researchers noted several limitations, including the possibility of missed or undiagnosed HSV-1 cases, especially in people who had the infection before entering the healthcare database.
Still, the message is clear: a virus often dismissed as a minor inconvenience might play a major role in long-term brain health.
“These results suggest that antiviral treatment could have a role in reducing the risk of dementia,” the researchers wrote.
The study adds fresh urgency to understanding how everyday viral infections could influence severe neurodegenerative conditions—and whether something as simple as early antiviral therapy might one day be part of the solution.
