The Mouth: Fun, Flirty, and Full of Bacteria
An Overview of the Mouth and Bacteria

Most people have personal reasons to practice good oral hygiene, whether to get a whiter smile, have minty fresh breath to impress a date, or just to prevent cavities that require an unfun visit to the dentist. But most people are unaware that good oral hygiene is vital to maintaining a balanced relationship among the millions of bacteria that live inside your mouth!

The bacteria behind kissing

Let’s say you’re on a date. Things are going really well, Marvin Gaye is playing in the background and you say to yourself, “Wow, I really want to kiss this person.” And you do and it’s fabulous and there are fireworks with foot-popping action and all that other good stuff. Well, not only did you share an emotional connection with that other person, but you have also exchanged 80 million bacteria per 10 seconds of kissing. Now that is intimate (1).                         

Meet the bacteria in your mouth

I know what you’re thinking: millions of bacteria living inside your mouth? Exchanging bacteria with other people? Gross. However, let’s put this into perspective; 90% of the cells in or on the human body are bacterial, fungal, or otherwise non-human (2). Our mouths alone are home to some 700 different species of bacteria that live in different microbial sub-habitats: teeth, tongue, lip, cheek, hard palate, soft palate, and tonsils. This collection of microorganisms is known as a microbiome.

You might be wondering, “what’s a microbiome” Well, each of us houses a complex ecosystem of bacteria within our bodies, and the collective genomes of all these microbes altogether create the human microbiome. Each person’s microbiome is unique and can identify individuals much like a fingerprint. In fact, while all human beings are 99.5% identical in genetic makeup, our microbiomes can be 100% different. (3) Watch the video below to learn more about the communities of bacteria inside your body that make you…well, you!  

The Oral Microbiome

Because it is the gateway to the rest of the body, the mouth contains one of the most significant microbiomes. It is the first meeting place between the outside environment and your body, so it is important to understand what kinds of bacteria hang out in there.

The oral microbiota can be categorized into 3 general groups:

  1. Symbiotic (positive relationship–they give us as good as they get from us);
  2. Commensal (most bacteria simply live within and on us);
  3. Pathogenic (disease-causing).

Recognizing the balance and shifts of these bacterial groups is an important part of maintaining a healthy mouth. These bacteria are especially important in the formation of plaque: one of the most prevalent substances in our mouths.

Plaques from bacteria in mouth
Source: Quick Meme

Bacteria and biofilm

For those that don’t know, plaque is the whitish film that you may find under your fingernail after scraping it against your tooth. “Plaque” is a nasty-sounding word (similar to “moist”) that aptly fits this film in which bacteria grow. Plaque is viewed negatively because, if not managed properly, it can lead to tooth erosion and the first stage of cavities (aka caries). However, plaque formation is inevitable, and it is therefore important to understand its general life cycle.

Bacteria make plaques in mouth
Source: Free Vectors

When saliva interacts with our enamel, a protective protein layer called the pellicle forms on our teeth. Aerobic (oxygen-loving) bacteria attach to the pellicle, forming a biofilm. These aerobes are typically symbiotes and commensals. Together, they form “buffer zone” that prevents acids in foods and beverages from directly contacting the enamel. However, as more microbes attach, the biofilm begins to thickens. These extra layers block oxygen from deeper levels of the biofilm and shift the environment from (high-oxygen) aerobic to (low-oxygen) anaerobic environment.

An anaerobic environment allows pathogenic anaerobic bacteria to colonize. Importantly, commensal bacteria can shift from symbiotic or pathogenic. A good way to think about this is behavior is by imagining what “bandwagoners” of sports teams would do. Just like how more people support the winning team than the losing one, commensal bacteria tend to swing in the direction (symbiotic or pathogenic) that has the upper hand at a given time (4).

“An unbalanced or unhealthy oral microbiome is like a garden overgrown with weeds”

-Gerry Curatola “The Mouth-Body Connection”

It is only when the mouth becomes overgrown with pathogens that the biofilm can be considered “bad” and detrimental to overall health. It turns out out that the anaerobic bacteria in plaque can release a variety of proteins into your body. These molecules can penetrate the lining of the gums, causing problems in places beyond the mouth (Lin 2018, pg. 99)
How bacteria affects the mouth

Because there is a lot of blood-flow in the gums, it is easy for pathogens, toxins, and other harmful complexes to disseminate to other regions of the body through the bloodstream. It’s like giving criminals a “Get Out of Jail Free” pass in Monopoly and then letting them take the railroads all over town.

That’s why it’s not only about how your mouth looks and smells, but also about what is going on inside your mouth. A balanced oral microbiome is affected by a variety of factors. These include types of food you eat, stress, age, genetics/race/ethnicity, gender, and even the type of toothpaste you use. Each of these factors contribute to the uniqueness of an individual’s microbiota composition, and making better lifestyle decisions can support a healthy oral microbiome. A few interesting ways to maintain balance within the oral microbiome can be found here.

Concluding Thoughts

The main takeaway of all this information is that putting the right foods in your body and practicing good oral hygiene will not only benefit your mouth, but will also help the rest of you body. However, if you’re still not sold on the idea that the mouth plays a large role in the body’s overall health, read the next post to find out how the oral microbiome is involved in the development of diseases like arthritis, cancer, cardiovascular disease, and autoimmune diseases!

Written by: Hailey Motooka, Bonnie Feldman, DDS, MBA, Ellen M. Martin


  1. Kort, Remco, et al. “Shaping the Oral Microbiota through Intimate Kissing.” Microbiome, vol. 2, no. 1, 2014, p. 41., doi:10.1186/2049-2618-2-41.
  2. Turnbaugh, Peter J, et al. “The Human Microbiome Project: Exploring the Microbial Part of Ourselves in a Changing World.” Nature, vol. 449, no. 7164, 18 Oct. 2009, pp. 804–810., doi:10.1038/nature06244.
  3. Rob Knight, and Daniel McDonald. “Our Second Genome.” Imagine, pp. 26–29.,
  4. Marsh, Philip D. “Dental Plaque as a Biofilm and a Microbial Community – Implications for Health and Disease.” BMC Oral Health, vol. 6, no. Suppl 1, 15 June 2006, doi:10.1186/1472-6831-6-s1-s14.
  5. Lin, Steven. The Dental Diet: the Surprising Link between Your Teeth, Real Food, and Life-Changing Natural Health. Hay House, Inc., 2018.


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