If theres billions of bacteria in our mouths, how come when we cut our inner lip we’re not guaranteed an infection?
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Your immune system for one. It’s what it is for after all.
Another is that not all bacteria in your mouth are necessarily the type that will cause an infection.
Not all bacteria try to kill you, some are good for you, some just exist and don’t do shit. We also have a immune system to fight the bad bacteria.
That’s why things like “more bacteria on your phone than on the toilet” are such bullshit things to say. Your phone has bacteria, but the toilet has shit and piss bacteria
You’re swimming in bacteria 24/7. It’s in the air, on the floor, in your clothes, stuck to your skin, in every orifice, in your food, etc.
The immune system copes with normal amounts of it or you’d literally die for trying to do the slightest thing on planet Earth.
What it can’t cope with is when the bacteria grows to enormous levels (which are still microscopic, but there’s a big difference between 1 bacteria per square mm, and 1,000,000,000 bacteria per square mm), or is of a type that can cause problems inside the body.
Pretty much, this is planet Bacteria far more than almost anything else. It’s actually posited as being a serious problem should we ever visit other life-bearing planets (or their inhabitants ever visit us). A billion new bacteria never-before-seen by our immune systems, or the immune systems of life on those planets, and you can wipe out entire civilisations (as has happened countless times in even human history).
You can’t live bacteria-free – hell, “you” are made up of a substantial portion of critical bacteria yourself, most of your digestive system for a start! It’s mostly problematic when you encounter new bacteria, unusual bacteria in places your body doesn’t normally have to deal with it (e.g. bacteria from soil on the surface of your food, etc.), or the bacteria are in overwhelming numbers because of conditions (e.g. food that’s gone rotten in a warm, damp climate where the bacteria feed and multiply like crazy).
Technically mouth wounds *are* infected. But we often use ‘infected’ to mean that our bodies are failing to fight off rapidly-growing bacteria, rather than that bacteria are present in an area.
Your immune system is there to take care of it. We have quite strong barriers of defence in any of these mucous membranes as they’re always exposed to a pretty nasty environment.
An interesting fact though is you do actually get small amounts bacteria into your blood stream when you have any kind of even minor trauma to your mouth, eg brushing your teeth. Poor dental hygiene is linked to systemic illness like heart disease.
>If theres billions of bacteria in our mouths, how come when we cut our inner lip we’re not guaranteed an infection?
Actually, you ARE guaranteed an infection. Every time there is a breach in the skin, there is an infection. Bacteria and viruses get in and start wreaking havoc. However, your immune system is quite adept at countering infections, so you may not even notice that it’s happening.
Kurzgesagt did a [great video](https://www.youtube.com/watch?v=lXfEK8G8CUI) on infections and the immune system.
There’s quite a few layers of lining to the mouth and the gut. Sooo when a cancer patient undergoes chemotherapy, the lining of the mouth (and also the lining of the guts) gets eroded, because chemotherapy targets the rapidly dividing cells, which includes the cells making up the lining. Chemotherapy also sometimes decreases your immune system’s capabilities. Because of this, when the lining of your mouth erodes, the inside of your mouth is more likely to get sores and ulcers. Chemotherapy patients are encouraged to brush their teeth four times a day to reduce the bacteria getting into those sores and making it worse, but brushing teeth can be painful due to the mouth ulcers, so you can get this medicated mouthwash that is mostly salt and baking soda, to use four times a day, to reduce the intensity of potential infections.
Edit: Hope this was tangential to what you asked.
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