Humans are superorganisms. This isn’t hubris but scientific fact: We’re a collective of not just our own cells but trillions of bacteria, viruses, fungi, and other microbes creeping along our insides and outsides. Called the microbiome, these tiny critters outman and outnumber human cells but are kept in check by a delicate equilibrium that science has found benefits us nicely, contributing to overall health and wellness.

When it comes to the body’s microbiome, the focus tends to linger on the gut. It’s only natural since gut flora is considered the largest microbiome in the body, impacting not just digestion but mental health, immune function, and even longevity. Yet there is another microbial ecosystem inhabiting our pearly whites: the oral microbiome. Emerging research shows that while this community of over 700 species plays an essential role in keeping the body healthy, it can also lead to disease when the equilibrium is tipped.

What is the oral microbiome?

While a portion of the body’s microbiome develops in utero, this teeny tiny motley crew is mostly established during early childhood, what microbiologists refer to as the first 1000 days. These bacteria like Lactobacillus — aka the “good” bacteria important for immune health — are passed along from mom during birth and in breastmilk and later, as we age, are pruned by diet, medications, lifestyle choices, immediate environment, and even genetics (studies have shown this can be a pretty persuasive influence). For this reason, no two people have identical microbiomes, although those who cohabit or live in the same household may have similarities.

The gut and oral microbiome are two of the largest microbial habitats of several in the human body. While connected by a long tube (aka your gastrointestinal tract), these niches are unique due to environmental pressures like oxygen exposure or nutrition but have overlapping functions like regulating our immune systems and defending against pathogens.

Within the oral microbiome, there are even more specialized “micro niches” on and under your tongue, at your gum line, near your second distal molar, and in your nose, Mark Burhenne, a functional dentist based in San Franciso, tells Inverse. Even the biofilm, a slimy, living layer of microorganisms that builds up on your teeth, is an essential part of your oral microbiome.

We swallow roughly a little over a liter of saliva a day containing far more bacteria than your average probiotic.

“Biofilm is what actually helps protect the teeth,” says Burhenne. “Biofilm is there to help pull calcium, phosphorous, hydroxyapatite, boron” all of which are needed to remineralize teeth.

When you’re brushing your teeth every morning, you’re actually thinning out this layer of biofilm, which allows it to operate normally and do its job. (You’re also reducing plaque, which is considered a combination of biofilm and food debris and responsible for both tooth decay and gum disease.)

How does the oral microbiome affect our health?

According to Dr. Stanley Hazen, a cardiologist who directs Cleveland Clinic’s Center for Microbiome and Human Health, we swallow roughly a little over a liter of saliva a day containing far more bacteria than your average probiotic. But the journey southward is less kind to oral microbes than it is to the Magic School Bus.

“The environment changes [as bacteria travel through the GI tract],” Hazen tells Inverse. “For example, the pH of saliva isn’t acidic but by the time you get to the stomach, you have a lot of acid there that alone kills off a large number of bacteria.”

Further down the line, Hazen says, bacteria from the mouth are killed off by the antimicrobial, low-oxygen environment of the intestines, which favor anaerobes, or bacteria that don’t need oxygen. Because of these chemical barriers and restrictive environment, scientists believe that for a healthy person, it’s nigh impossible for oral bacteria to successfully relocate to the gut.

In individuals with gut microbiomes teeming with robust, protective bacteria, that’s usually the case but not for those with or at risk for disease, says Hariom Yadav, an associate professor of neurosurgery and brain repair at the University of South Florida’s Institute for Microbiomes.

“If someone has a genetic susceptibility and then on top of that there are these microbial or environmental factors overlaid, then in one person [these bacteria] can actually trigger the disease pathology much faster,” Yadav tells Inverse.

An out-of-whack oral microbiome may instead infiltrate the circulatory or lymphatic system, perturbing not just gut flora but any organ or region of the body.

How this happens plays out in a couple of ways. If there are more bad bacteria than good ferried by saliva, they can directly invade the gut microbiome and disrupt its harmony. For example, the bacteria Porphyromonas gingivalis — involved in periodontitis, or gum disease — have been implicated in gastrointestinal and pancreatic cancers. Some research suggests that gut conditions like inflammatory bowel disease or Crohn’s disease may be due to a common oral bacteria called Klebsiella replacing or outcompeting the normal microbes in the colon.

An out-of-whack oral microbiome may instead infiltrate the circulatory or lymphatic system, perturbing not just gut flora but any organ or region of the body. For instance, gum disease, which is incredibly common affecting nearly 50 percent of adults aged 30 and older and 70 percent aged 65 and older, creates an inflammatory oral environment that promotes bleeding and softens up gums. Pathogenic bacteria like P. gingivalis, Streptococcus, and Fusobacterium nucleatum and the toxic chemicals they produce slip through without resistance like a nightclub without a bouncer.

Yadav says this is potentially how gum disease is strongly linked to Alzheimer’s disease, dementia, and even hypertension where unhealthy bacteria are believed to impair the production of nitric oxide, which regulates blood pressure. Hazen says there’s mounting evidence to suggest a causal relationship between gum disease and heart disease, which is the leading cause of death in the US. However, it’s not quite clear yet exactly which of the 300 known gum disease-causing bacteria are responsible (it’s a bit more clear-cut when it comes to the gut microbiome).

How to cultivate a healthy oral microbiome

Scientists still have a lot of work to do in fully sussing out the oral-gut microbiome axis. But to Burhenne, who goes by @askthedentist on TikTok, there’s no doubt in his mind the key to a healthy gut and body starts in the mouth.

“Unfortunately, in today’s world, we’re doing so much harm, we’re killing the oral microbiome so it can’t do its job,” he says, the suspects of which are the usual: poor oral hygiene and practices, poor diet, and not getting routine dental care (older adults typically fall off the bandwagon on this one, says Burhenne).

Rectifying these habits to bring balance to your oral microbiome may not completely cure or reverse maladies such as Alzheimer’s disease (especially again as there’s no precise connection, yet). But there are a few studies suggesting improved oral health could reduce your risk of developing heart disease and others. Aside from regular tooth brushing, flossing, and seeing your dentist instead of avoiding them, Burhenne recommends steering clear of mouthwashes that contain alcohol, which kills good and bad bacteria indiscriminately, and using a prebiotic, hydroxyapatite-based toothpaste, which can feed and promote a healthy oral microbiome as well as protect tooth enamel.

Burhenne recommends brushing or scraping your tongue regularly to cut down on the microbes that like to nestle alongside your tastebud and in addition, a viral social media trend: Oil pulling. This Ayurvedic practice has been used for centuries to improve oral health. Much like using mouthwash, the oil — typically a spoonful of coconut oil — is swished around in the mouth to remove bacteria and thin out biofilm. Some small studies in 2016 and in 2020 show oil pulling may be helpful. However, the technique can be overused (Burhenne advises swishing for no more than three to five minutes ) and do more harm than good, especially if you’ve got a case of gum disease. It can also only do so much.

“My pet peeve are all these patients that never see their dentist, they have gum disease and think oil pulling is going to take away their gum disease,” says Burhenne. “No, it won’t.”

Even with all the brushing and oil pulling in the world, achieving a balanced oral microbiome isn’t possible without the right diet (just as it is for the gut microbiome). That means avoiding sugary foods bad bacteria feast on and chomping down on leafy greens, cheeses, proteins, and nuts.

“You can’t ignore your mouth if you want to be healthy,” says Burhenne. That’s likely a truth all five dentists can agree with.