Despite growing worldwide concern regarding overuse of antibiotics and the loss of microbial species in the human microbiome (what microbiologists call “the disappearing microbiome”), there is still the widespread notion that being squeaky clean is a good idea. Watch TV or read magazines and you will see ads for disinfectants making claims such as “Kills 99.9% of germs on contact,” or mouthwashes that claim “Kills 99.9% of germs that cause bad breath.”
Whether it’s a disinfectant used on countertops or mouthwash to eradicate mouth microbes, are these really necessary? Is it healthy?
Let’s break down the microbes that are not healthy for humans into broad categories:
- Viruses spread from other humans—COVID-19 and the flu virus are the obvious examples in our present world. Exposure to people carrying these viruses allows rapid spread of the virus.
- Fecal bacteria—that you can acquire from doorknobs or a tainted hamburger prepared by a kid who went to the bathroom and didn’t wash his hands.
- Pathogenic bacteria—You will recognize these as the species causing, for instance, pneumonia, meningitis, or urinary tract infections, such as Pseudomonas aeruginosa, Escherichia coli, and Klebsiella pneumoniae. These are often serious infections.
- Non-pathogenic bacteria but with unpleasant effects—Or microbes with limited potential for harm. This would include hydrogen sulfide-producing species in the mouth responsible for bad breath, Streptococcal species that cause tooth decay, Desulfovibrio in the gastrointestinal (GI) tract that causes diarrhea, H. pylori in the stomach that can encourage small intestinal bacterial overgrowth, SIBO.
All this gives microbes a bad name. Like many other generalizations, it leads to false conclusions. It causes people to think that all microbes are bad and that your mouth, skin, and countertops need to be sterilized, i.e., completely free of all microbial life and squeaky clean.
This is a really bad idea. We are currently experiencing a flood of new observations on the health benefits of the microbial world. Not only do we harbor harmless residents in every inch—external and internal—of our bodies, but we actually need them to perform crucial functions. Among the beneficial functions performed by various microbial species in the body:
- Discourage proliferation of unhealthy species—Species of Lactobacillus and Akkermansia, for instance, keep Klebsiella and Fusobacteria from overproliferating.
- Stimulate intestinal mucus production—Akkermansia is a winner here, too.
- “Crosstalk” with endocannabinoids, the signaling system that helps regulate the intestinal barrier
- Produce essential vitamins—Intestinal microbes produce vitamins B1, B2, B3, B6, B9, B12, and K2, among others.
- Produce essential fatty acids—Intestinal butyrate produced by butyrate-producing species such as Faecalibacterium prausnitzii help control insulin resistance, blood sugar, blood pressure, and triglycerides.
- Help regulate hormonal activity—The so-called “gut-brain axis” transmits signals to influence activity of the hypothalamus and pituitary glands in the brain. Our friend, oxytocin, for instance, is released by the activity of Lactobacillus reuteri.
- Influence brain activity and mood—Microbes in the GI tract can increased production of brain growth factors such as brain-derived neurotrophic factor, BDNF; cause deeper sleep and extend REM sleep; determine whether you are anxious, happy, sad, or mad. Some of these effects are vagally-mediated (i.e., transmitted via the vagus nerve), some are due to various microbial metabolites, others are indirect via endotoxemia.
- Regulate intestinal activity—Microbes participate in a dizzying array of functions in the GI tract: mucus production, metabolite production, nutrient production, and others.
Unfortunately, efforts to be squeaky-clean and as free of microbes as possible is one of the reasons why people experience so many health problems. Eczema on the skin, for instance, is likely worsened by inadvertent efforts like excessive hand cleaning that leads to proliferation of Staphylococcus aureus that overpowers the harmless commensal (resident) Staphylococcus epidermidis. An antibiotic taken for questionable indication, such as to “prevent” bacterial pneumonia during an upper respiratory viral illness, can lead to proliferation of Clostridium difficile in the GI tract: C. diff enterocolitis, a bad situation. Antibiotics, needed or not, can wipe out species from the GI tract forever, eradicating species such as L. reuteri responsible for oxytocin production in the brain. Swishing your mouth with mouthwash raises blood pressure (due to reduction in nitric oxide production by bacteria) and changes oral flora composition. (Ironically, one of the changes in bacterial composition with mouthwash is a shift towards enrichment with species typically found in fecal material, i.e., Proteobacteria.) The practice of vaginal douching alters vaginal flora and has been associated with increased risk for pelvic inflammatory disease.
While humans are not designed to share the microbiomes, skin and otherwise, of thousands of other people, you are meant to share the microbiomes of your family and close contacts. People touch, kiss, have sex, share the air and contact surfaces and thereby share microbes. We are supposed to be exposed to the variety of microbes in the air, food, soil, animals, and water and thereby maintain a vigorous immune response if and when we are exposed to a potential pathogen.
During a pandemic, you may indeed have to wear a mask and avoid touching strangers, but don’t overdo it in other circumstances. Touch the ground, even go barefoot now and then, use soaps and other toiletries sparingly, brush your teeth and avoid grains and sugars but save your money on the mouthwash. Enjoy the close contact of people you live with or in your family, enjoy your dog, cat, or other creature, and put away the Lysol.