There are more microbes in the human body — a number estimated to be in the trillions — than there are stars in the Milky Way.
All of your microbes combined weigh about as much as your brain: about three pounds.
Microbes cover your skin from head to toe; and their diversity can vary depending upon your skin temperature, texture, thickness, humidity, and chemistry.
For instance, women's hands typically harbor more lactic acid bacteria — which food purveyors use to ferment wine, pickles, and yogurt — than men's hands.
Men's hands, on the flip side, generally have more corynebacterium bacteria, which play a role in synthesizing monosodium glutamate, or MSG.
Your left hand could have a different microbial community than your right hand.
And more microbial cells live inside the human body than there are human cells.
Microbes keep your vital organs — such as your brain, digestive system, and immune system — working properly.
In fact, your digestive tract alone — including your small and large intestine — houses about 99% of your entire microbiome.
The microbial genes in your body outnumber the genes in your own DNA by more than 100 to one.
At least 1,200 different types of bacteria live in your mouth. Most are either benign or protect you from infection, but some are bad and can cause tooth decay, bad breath, and gum disease.
They can produce foul-smelling sulfurous chemicals in your mouth while you sleep, which, if not washed away by your saliva can cause you to wake up with "morning breath."
There are hundreds of different microbial species swimming on and inside your body at any given time.
And no two people have the exact same mix of microbes.
Researchers have even found that your dog's tongue and paw microbes could colonize your own skin.
Research suggests that the microbiome plays a role in digestion, the regulation of your immune system, disease prevention, wound healing, gut lining protection, appetite control, brain development, and even your emotions.
Scientists have also seen evidence that your microbial communities play a role in depression, allergies, asthma, obesity, and anxiety — though these are just preliminary, correlative results.
The bacterial microbes that line your skin are constantly battling other nasty invaders, such as the fungus that causes athlete's foot and other bad microbes that could cause infection.
Your skin bacteria also synthesize many useful compounds for the body, including antibiotics and acids that kill other harmful microbes, and carbon dioxide, which can slow the growth of fungus.
A developing fetus is almost completely sealed off from its mother's microbes in the womb, which could be deadly to the fragile child.
Just before birth, a pregnant woman's vagina acquires new bacterial species that, if she weren't about to have a baby, would normally live in her gut.
These species then get pushed into the baby's skin, eyes, and mouth as it passes through the birth canal during vaginal birth.
This literal "mouthful" of microbes sets up a newborn's own microbiome for a healthy start.
The birth canal also supplies newborns with the bacteria Lactobacillus, which helps the baby digest milk and develop the immune system.
And breast milk supplies babies with a healthy dose of bacteria.
In fact, new research suggests that about 10% of every woman's breast milk contains complex carbohydrates that cannot be digested by the infant, but which fortify an infant's microbiome bacteria. This suggests a long coevolution humans have had with these organisms.
Babies born via C-section don't get bathed in good birth canal bacteria, but instead attain the bacteria from the doctor's hands or whatever else may have been lingering in the hospital room.
As a consequence, scientists believe that C-section babies might have slightly heightened risks of developing allergies, asthma, gut infections, and diabetes, though these long-term risks are not as well-understood.
Scientists are experimenting with swabbing newborn C-section babies with bacteria from the mother's birth canal to replace what they missed during the delivery. If studies demonstrate long-term benefits, this may become a standard practice.
The composition of your microbiome can change at different points in your life, with the biggest shifts occurring during adolescence, pregnancy, old age, and after a big diet change.
