May 28, 2025
The virus that causes cold sores, the painful blisters that erupt around the mouth and lips, may be linked to an increased risk of Alzheimer’s disease, according to a new report. The good news is that antiviral medications that target cold sores may be effective in lowering Alzheimer’s risk, the study findings suggest.
An estimated two-thirds of adults are infected with the cold sore virus, a type of herpes virus known as herpes simplex virus type 1, or HSV-1. Most of the time, the herpes virus remains sequestered in nerve cells and does not cause symptoms. However, periodic flare-ups can occur, especially during times of stress, sunburn, illness or fatigue.
Cold sores, also known as fever blisters, begin with numbness or tingling in an area on the edges of the lips, followed by redness and swelling and then the painful and raw open sores. The sores usually resolve after a week or so, though healing can be sped up with antiviral medicines. Drugs used to treat cold sores and other herpes infections include acyclovir (brand name Zovirax), valacyclovir (Valtrex), and famciclovir (Famvir).
For the study, researchers combed through an extensive database of health records of American adults from 2006 to 2021. They matched people according to their age, sex, where they lived, and how many doctor visits they had. They identified 344,628 patients with Alzheimer’s disease and compared them with 344,628 peers without Alzheimer’s. Their average age was 73.
Not surprisingly, the risk of Alzheimer’s increased with advancing age. But the researchers also found that those with Alzheimer’s disease were 80 percent more likely to have an HSV-1 diagnosis.
Among those infected with HSV-1, about 40 percent used an antiviral medicine to relieve cold sore outbreaks. Those who used a herpes-fighting medication were 17 percent less likely to develop Alzheimer’s than their peers who didn’t use such treatments.
“While the molecular mechanisms remain to be fully elucidated, these results are indicative of a possible role for antiherpetic therapy in mitigating dementia risk,” the study authors concluded. The findings were published in the journal BMJ Open.
The researchers also looked at the potential role of other herpes viruses in the onset of Alzheimer’s disease. These included HSV-2, a related herpes simplex virus implicated in genital herpes outbreaks; varicella zoster virus, a herpes virus related to chickenpox and shingles outbreaks; and cytomegalovirus, a herpes virus that causes a mononucleosis-like illness. Both HSV-2 and varicella zoster virus infections were also associated with a heightened risk of Alzheimer’s disease.
The researchers aren’t sure why HSV viruses might raise the risk of dementia. “However, studies have shown that inflammatory alterations in the brain caused by HSV infection are pivotal in Alzheimer’s disease development,” the authors note.
The study showed only an association between cold sore virus infection and Alzheimer’s risk and cannot prove cause and effect. But earlier research suggests links between herpes infections and an increased Alzheimer’s risk. Studies have found, for example, that HSV infections appear to raise levels of toxic beta-amyloid in the brain, which can clump together to form the telltale brain plaques of Alzheimer’s disease. Another recent study found that people who receive the shingles vaccine, which targets the varicella zoster virus, might be protected against Alzheimer’s disease as well. Other research suggests that people carrying the APOE-E4 gene variant, the most common genetic risk factor for Alzheimer’s disease, are more susceptible to symptomatic HSV infections.
The findings add to growing evidence that various infections may play a role in Alzheimer’s onset, though more research is needed to better understand potential links. Still, if you suffer from cold sores, it might be a good idea to treat it with medication. It may not only shorten cold sore healing time but could help to protect your brain.
By ALZinfo.org, The Alzheimer’s Information Site. Reviewed by Eric Schmidt, Ph.D., Fisher Center for Alzheimer’s Research Foundation at The Rockefeller University.
Source: Yunhao Liu, Christine Johnston, Madine Jarousse, et al: “Association between herpes simplex virus type 1 and the risk of Alzheimer’s disease: a retrospective case-control study.” BMJ Open, May 20, 2025
