A new study has found that the virus that causes cold sores may be linked to a higher risk of developing Alzheimer’s disease.
Researchers analyzing the medical records of over 344,000 adults have found that individuals infected with herpes simplex virus type 1 (HSV-1)—the virus most often behind cold sores—were significantly more likely to be diagnosed with Alzheimer’s disease later in life.
The study, published in BMJ Open, matched more than 300,000 people over the age of 50 into two equally sized groups: one with Alzheimer’s and one without. Among them, 1,507 people with Alzheimer’s had a history of HSV-1, compared to just 823 in the control group.
According to the findings, having HSV-1 increased the likelihood of developing Alzheimer’s by 80%. This association remained even after adjusting for other known risk factors, including carrying two copies of the APOE4 gene—one of the strongest genetic links to Alzheimer’s.
The study also explored the potential protective effects of antiviral treatments. Roughly 40% of those diagnosed with HSV-1 had received anti-herpetic medication, and they were found to be 17% less likely to develop Alzheimer’s than those who hadn’t received such treatment. The results suggest that antiviral therapy may reduce inflammation or viral activity in the brain, potentially lowering the risk of neurodegeneration.
Researchers stressed that the study does not prove causation. “This research is based on information gathered from using health records and administrative claims data,” said Dr. Sheona Scales, Director of Research at Alzheimer’s Research UK.
She added that HSV-1 infections are often asymptomatic, meaning many infections may have gone unrecorded. Furthermore, Alzheimer’s is notoriously difficult to diagnose in its early stages, which complicates research based solely on electronic records.
While HSV-1 causes most cold sores, the virus can also lie dormant in nerve cells for years without noticeable symptoms. Experts believe that in some individuals, the virus may reactivate and trigger inflammation in the brain, which over time could contribute to the kind of neuronal damage seen in Alzheimer’s disease.
Women accounted for 65% of the Alzheimer’s cases in the study, with an average age of 73 and a higher rate of underlying conditions—many of which are already known to influence dementia risk.
Though the link between viruses and cognitive decline is not fully understood, the study reinforces calls for broader public health attention. “This analysis places an even greater emphasis on viewing the prevention of herpes viruses as a public health priority,” the authors said in a statement.
Alzheimer’s remains the most common form of dementia, affecting over 6 million Americans. With no known cure, research into risk factors—including viral infections—continues to be a top priority for scientists.
Still, experts caution that more work is needed before changing clinical recommendations. “We know there are 14 established lifestyle and environmental risk factors for dementia,” Dr. Scales noted. “There’s not enough evidence yet to include infections like HSV-1 on that list.”
Even so, the possibility that cold sore treatments might one day help reduce Alzheimer’s risk offers a new direction for future studies—and potentially, new hope for prevention.