April 25, 2025 – You've heard of the gut microbiome – but did you know your mouth has one too?
Home to roughly700 species of bacteria, viruses, fungi and other microbes, youroral microbiome is the second mostdiverse microbiome in the body (after the gut) and it plays a key role in your health. Now, new research from the University of Sydney suggests that specific species could be triggering migraines.
In thestudy, more than 150 women under age 75 filled out a questionnaire about their oral health based on the World Health Organization'soral health survey. They were assessed for migraine, body pain, headaches, and abdominal (belly) pain. They also submitted saliva samples, which were analyzed for microbiota (the things living in the samples).
The connection between oral health and pain was overwhelming.
"Even before we had the microbiome data back, I was evaluating the survey data and found incredibly strong signals for oral health and every measure of pain that we used," said lead author Sharon Erdrich, a PhD candidate in the Faculty of Medicine and Health at the University of Sydney.
When it comes to headaches, the connection to oral health is well-established: Jaw pain can travel up andtrigger a migraine. A2020 study by researchers in Korea, for example, found a link between migraines and TMJ (adisorder of the temporomandibular joint, which connects the skull to the jaw).
But Erdrich and her colleagues looked deeper. With the oral microbiome data, they could tease out connections between microbiota and specific types of pain. Among people in the study with migraines, a bug called Mycobacterium salivarium stood out.
The finding builds on previous research hinting at the oral microbiome's role in pain. Researchers have isolated Mycobacterium salivarium in the joints of people withTMJ, for instance. A2016 study at the University of California San Diego identified more nitrate-reducing microbes in mouths of people with migraine.
Though the research is early, it underscores the importance of good oral health for preventing migraines and other types of pain.
How Do Migraines Start in the Mouth?
Scientists are still uncovering exactly how microbes contribute to pain.
"We're not sure if it's the bacteria themselves that's the mechanism, rather than the pro-inflammatory peptides that they produce," Erdrich said.
One type of mouth bacteria – called Aggregatibacter actinomycetemcomitans (Aa) – produces peptides that signal the body to create antibodies, triggeringrheumatoid arthritis. And elevated levels of another peptide – calcitonin gene-related peptide, a key player in migraines – "have been observed in patients with both periodontitis and chronic migraine," according toMei-Hsuan Lee, PhD, a professor at the Institute of Clinical Medicine at National Yang Ming Chiao Tung University in Taiwan.
Complicating matters is the role of genetics. About 40% to 50% of the risk of migraines can be traced back to your genes, estimates show.And there are "multiple genes" that affect how likely you are to get migraines, according toEric Viirre, MD, PhD, a professor in the Department of Neurosciences at the University of California San Diego.
"All of these pain syndromes – fibromyalgia, chronic pain syndromes, and TMJ, for example – have multiple factors," he said. "Disambiguating these things is our big challenge."
Introducing the 'Oral Microbiome-Nervous System Axis'
One possibility could be something researchers are calling the "oral microbiome-nervous system axis," Lee said.
Poor oral health – and in particular, the presence of specific oral pathogens – may lead to systemic inflammation, activating the brain's immune system.
Asneurotransmitters carry pain signals to the brain, microbes can attach to them along the way, triggering migraine, Viirre said. (Nitrates, for instance, are known migraine triggers. When nitrates enter your system, they can attach to neurotransmitters, inducing a migraine.)
"What we don't know is where these different influences might be in the microbiome," Viirre said. "There's steps along the way in the pathways. Where do these things attach? How do they attach? How do they adjust? We're still learning about that."
What's Next?
Erdrich hopes to study treatments that target the oral microbiome in people who have migraines. Those interventions could include oral health practices, like more regular visits to a dental hygienist, along with probiotics and dietary changes "to restore a balance of bacteria in the mouth, that helps to keep the pathogens at bay," she said.
Viirre, a doctor in the Department of Neurology at UCSD with "a very large cohort of migraine patients," hopes that bothmicrobiome and genetic screenings will become affordable to patients within three to five years. Eventually, those patients could fit into categories for which there are targeted dietary and medical interventions.
"We're getting closer to those things now," Viirre said. "With agreat study like this, with important information about various species, we have some clues."
