The Mouth: Fun, Flirty, and Full of Bacteria

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

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!

So let’s say you’re on a date,

Mouth full of bacteria
Source: The Dental Floss

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).                         

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 aggregation of microorganisms is known as a microbiome.

What the heck is a microbiome?

Each of us incorporates an internal complex ecosystem of bacteria within our bodies, and the collective genomes of all these microbes altogether create the human microbiome. The microbiome is highly individual and could identify individuals much like a fingerprint. For this reason, while all human beings are 99.5% identical in genetic makeup, our microbiomes can be 100% different between individuals. (3) Watch the video below to learn more about the communities of bacteria inside your body that make you…well, you!  

The Oral Microbiome

The mouth contains one of the most significant microbiomes, because it is the gateway to the rest of the body. It is the first meeting place between the outside environment and your immune system, gut, and the signalling molecules they secrete to deal with the messy nutrients and toxins of food and outside microbes (including pathogens) that you take in.

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).

Recognition of the balance and shifts of these bacterial groups is essential to sustaining an optimally healthy mouth. They are especially important in the formation and understanding of plaque, one of the most prevalent substances in our mouths.

Plaques from bacteria in mouth
Source: Quick Meme

Mmm, Plaque

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 horrid-sounding word (similar to “moist”) that aptly fits this sticky deposit on teeth in which bacteria proliferate. 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 important to note its general life cycle.

Bacteria make plaques in mouth
Source: Free Vectors

When saliva interacts with the surface of 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 forming a “buffer zone” that prevents acids in foods and beverages we eat and drink from direct contact with our enamel. However, as more microbes attach and the biofilm thickens, it blocks oxygen from deeper layers creating a shift from an (high-oxygen) aerobic to a (low-oxygen) anaerobic environment. An anaerobic environment allows pathogenic anaerobic bacteria to colonize. Importantly, commensal bacteria can shift to being either symbiotic or pathogenic, like “bandwagoners” of sports teams (e.g. the majority of Golden State Warriors fans), in which more people support a winning team than a losing one. Commensal bacteria tend to swing in whichever 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 plaque biofilm can be considered “bad”, or detrimental in terms of overall health. The good aerobic bacteria are replaced by anaerobic bacteria, which release a variety of biologically active products that can penetrate the lining of the gums and set off an inflammatory cascade as seen in the figure below (Lin 2018, pg. 99)
How bacteria affects the mouth

Due to the rich vascularization of the tissues that compose the oral cavity, 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 what goes into your mouth, or how your mouth looks and smells, but what is going on inside your mouth as an ecosystem. A balanced oral microbiome is affected by a variety of factors, including types of food you eat, stress, aging, genetics/race/ethnicity, gender, even the type of toothpaste you use. Each of these factors contribute to the uniqueness of an individual’s microbiota composition, and practicing consistent oral hygiene and making better lifestyle decisions supports this healthy oral microbiome. A few interesting ways to maintain balance within the oral microbiome can be found here.

The main takeaway for all of this information is that a basic cognizant awareness of putting the right foods in your body and simply brushing and flossing twice a day will not only benefit your mouth, but it will benefit the rest of your body as well. However, if you’re still not sold on the idea that the mouth plays a larger role in the body’s overall health than previously thought, read the next post to find out how the oral microbiome is involved in the explanation and prevention of common systemic diseases such as arthritis, cardiovascular disease, cancer, and even some autoimmune diseases!


  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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