Finding the cause of Alzheimer’s—and hopefully, a cure—has long seemed like the search for the Holy Grail. But new breakthrough research may be uncovering a critical clue to this debilitating neurodegenerative disease. Hint: The clue may be hiding in our mouths.

Researchers have suspected that brain infection is at the root of Alzheimer’s disease. For one thing, people who have died with the disease show inflammation in their brains similar to the kind caused by infection. People with Alzheimer’s also frequently have chronic periodontitis, a gum infection, which is known to also affect other parts of the body, such as the heart. But it has not been clear whether gum disease causes Alzheimer’s…or if the poor oral hygiene common among Alzheimer’s patients causes gum disease.

In a new study, researchers from the US, Europe, New Zealand and Australia looked for Porphyromonas gingivalis, a bacterium that causes gum disease, and toxins released by P. gingivalis in brain samples from people who had died with Alzheimer’s.

They found the toxins in nearly all (up to 99%) of the brain samples…with the highest concentrations in samples that had the most beta-amyloid plaques and tau tangles, classic hallmarks of Alzheimer’s.

The researchers had also looked at brain samples from people without Alzheimer’s and found that while some had P. gingivalis and beta-amyloid proteins, they were at low levels. Since plaques and tau tangles accumulate in the brain for years before Alzheimer’s symptoms appear, the new research may have found the evidence that P. gingivalis may cause Alzheimer’s…rather than be the result of the disease.

To test that theory, the researchers gave P. gingivalis gum infections to mice—and found that the infection did spread to their brains…and also led to beta-amyloid plaques, tau tangles and neurodegeneration similar to what is seen in brains with Alzheimer’s.

While these findings are exciting and potentially a major breakthrough, Alzheimer’s is a complex disease. For instance, there is evidence that genes may play a role in development of the disease. Many questions remain unanswered and more research is needed to fully understand these new results and how best to use them.

Promising: This study, which was sponsored by Cortexyme, a San Francisco–based biotech company, also looked at whether it was possible to block the toxic effects of P. gingivalis. They found that antibiotics, a common treatment for people who have gum infections, had no effect on brain infection in the mice. But an oral drug the researchers developed specifically for the study not only blocked the gingipain toxins—it also halted the brain degeneration. The drug specifically inhibits the different types of gingipains enzymes secreted by P. gingivalis by irreversibly binding to the active catalytic site of the gingipains enzymes, permanently inhibiting their activity. Phase 2 clinical trials to test the drug on people with mild to moderate Alzheimer’s are planned for later this year.

In the meantime, it doesn’t hurt to be vigilant about oral hygiene. Not only will your teeth thank you, so will the rest of your body—and you just may be protecting your brain from getting Alzheimer’s.