How Microorganisms in Your Mouth Influence Your Health

Your mouth is more than just teeth, gums, and a tongue. It is also home to billions of microscopic organisms that can only be seen under a microscope. These include bacteria, fungi, and viruses. Collectively, the community of microorganisms living in your mouth is called the oral microbiome.

Researchers believe the oral microbiome may play a role in diseases that affect not only the mouth but also other parts of the body. Studying these microbes could open the door to new strategies for preventing and treating a wide range of health conditions.

Who Lives in the Mouth?

The mouth provides an ideal environment for microbes to thrive. Scientists estimate that about 700 different species can inhabit the human mouth. Some of these organisms may contribute to disease, while others help keep harmful microbes under control.

“Having microbes in your mouth is completely natural,” explains Dr. Christian Abnet, an oral cancer researcher at NIH. “Even individuals who practice excellent oral hygiene have a rich and active microbiome.”

In adults, the types and proportions of microbes in the mouth tend to remain relatively stable over time. However, when this balance shifts, it can signal trouble.

“People usually carry specific microbes in certain proportions,” says Dr. Akintunde Emiola, who studies the oral microbiome at NIH. “When those proportions change, it can be associated with disease.”

Scientists are still working to determine exactly which microbes are linked to particular illnesses. Understanding how changes in the oral microbiome contribute to disease remains an active area of research.

Effects Beyond the Mouth

Bacteria are among the most well-known microbes in the mouth. Dentists often warn that bacteria that feed on sugar can damage teeth and gums. These bacteria accumulate in dental plaque—the sticky film removed during cleanings.

But the impact of oral microbes extends far beyond cavities and gum disease. Studies have connected the oral microbiome to conditions such as cancer, heart disease, diabetes, allergies, asthma, and even Alzheimer’s disease.

For instance, research suggests that poor oral health is associated with a higher risk of developing Alzheimer’s disease. Inadequate dental care may allow harmful bacteria to flourish.

“We believe certain bacteria in the mouth may release substances that enter the bloodstream, reach the brain, and disrupt normal processes,” says Dr. Colin Combs, a specialist in neurodegenerative diseases at the University of North Dakota.

Combs and his colleagues have identified beta-amyloid—a protein strongly linked to Alzheimer’s disease—in saliva. In the brain, beta-amyloid forms clumps known as plaques. Their findings suggest it may also play a role in the mouth.

The team is investigating how beta-amyloid in saliva interacts with oral microbes and whether it contributes to Alzheimer’s disease development.

Cancer risk may also be influenced by the oral microbiome. Abnet’s research has found associations between certain oral microbes and increased risks of cancers affecting the lungs, colon, and esophagus.

There are several possible explanations. Some bacteria produce carcinogens—substances that can promote cancer. In addition, the oral microbiome can influence the immune system, the body’s defense against infection.

One key immune response is inflammation, characterized by heat, swelling, and redness. While inflammation helps fight infections, chronic inflammation is linked to many diseases, including cancer and Alzheimer’s disease.

Changes in immune activity may also help explain connections between oral microbes and allergies. Allergies occur when the immune system overreacts to normally harmless substances. For example, one study found that children with certain oral bacteria needed only a small amount of peanut exposure to trigger an allergic reaction.

By uncovering how oral microbes contribute to disease, researchers hope to develop more effective treatments.

“Understanding the mechanisms is essential if we want to design targeted interventions,” Abnet notes.

Keeping Microbes in Balance

Eliminating harmful microbes in the mouth is challenging. Antibiotics can kill bacteria, but they often wipe out beneficial microbes along with harmful ones. Emiola’s team is therefore exploring more precise approaches.

“When you eliminate all microbes, the harmful ones often return more quickly,” Emiola explains. “If you target only the problematic bacteria, the beneficial ones can help restore balance.”

One strategy involves bacteriophages—viruses that infect specific types of bacteria. Using bacteriophages that target harmful oral bacteria could provide a highly selective way to control disease-causing microbes.

Emiola’s group is also developing specialized treatments known as prodrugs. “Prodrugs are inactive compounds,” he says.

These compounds are designed to become active only once inside specific bacteria. Once activated, they function similarly to antibiotics, but with greater precision.

The team has already developed a promising prodrug that targets bacteria responsible for severe gum infections. This approach could eventually have applications beyond oral health.

Meanwhile, many probiotic and prebiotic supplements are marketed as ways to improve the microbiome. Prebiotics promote the growth of certain microbes, while probiotics contain live beneficial organisms. However, scientists still lack clear evidence about which specific microbes—or combinations—provide meaningful benefits.

“There’s very limited solid evidence supporting particular supplements,” Abnet says. “So they’re not something I would routinely recommend.”

Fortunately, proven strategies for maintaining a healthy oral microbiome already exist. Good dental hygiene, regular brushing and flossing, and a balanced diet all support a healthy microbial environment. In fact, habits that promote overall health also tend to benefit the mouth’s microbial community.

“In the future, we may develop microbiome-based treatments that truly help people,” Abnet says. “But this field of research is still in its early stages.”

Adopting healthy daily habits remains one of the best ways to protect both your overall well-being and the microscopic community living in your mouth.