In January I had my wisdom teeth removed and was left with two gaping black holes at the back of my mouth. I was
instructed to keep these holes clean using a syringe to squirt salt water into them. But one day while I was measuring out my quarter teaspoon of salt into a cup of water I wondered, why salty water?
For simple irrigation purposes water would do the trick in washing out the, quite frankly, amazing quantity of food that buried into the back of my mouth after every meal. Yet salt water had been specified, I took to the internet to find out why.
Bacterial preferences
Web sources were adamant about three main things:
- salt water is an antiseptic- stopping the growth of bacteria
- salt water can be bactericidal- killing bacteria
- salt water reduces swelling, which soothes wounds
I already knew that bacteria have specific tastes in where they like to hang out and are well
adapted to thrive in those environments. Salt is one of those environmental conditions that bacteria tend not to like, with exposure to large quantities, such as in food preservation, being lethal to most species.
I was curious to know how salt is antiseptic and bactericidal, and how does it reduce swelling?
The Osmotic Argument
The theory is that salt exposure causes most bacteria to shrivel up and die using THE FORCE.
Okay, it’s more of a rule of nature, called osmosis. Osmosis moves water from areas where there is lots, to where there is little, until an even distribution is established. This seems to keep the peace in a cellular environment, a bit like when as a child you had to split a bar of chocolate with your brother, you split that thing evenly or all hell would break lose.
Osmosis means that when bacteria are exposed to a salty environment, they lose water, and if enough water is lost the bacteria shrivel up and die.
Wolah!
………….But there’s a crucial detail missing: We might understand why a high quantity of salt in preservatives is bactericidal, but what about when a little salt is dissolved and diluted in water?
Unfortunately, I couldn’t find any studies directly testing the effect of salt water on bacteria, so no clear answer is available 😦
It was at this point that I began to wonder what effect salt has on our cheek cells- if salt water washes are osmotic killers of bacteria would our own cheek and gum cells, subject to the same osmotic laws, be adversely affected?
No our cheek and gum cells do not shrivel and die in response to salt water mouth washes; I am a witness to that. However, some osmosis is thought to occur. Not enough to kill cheek/gum cells, but enough to reduce the post dental surgery swelling.
But do bacteria also survive the tiny osmotic effect of a saltwater wash? Or are bacteria more sensitive to the tiny amounts of salt than our cells? Does salty water have a temporary effect on bacterial growth?
With no studies examining this it is difficult to feel convinced by the osmotic argument, is there a better explanation?
The pH Argument (Acid, or maybe Alkali?)
I found two sites that contended the importance of salt water rinses in temporarily changing the pH of the mouth, which was argued to be a disadvantage for bacterial growth. The problem was one site stated that salt water makes the mouth acidic and the other alkali.
Opposite claims, which isn’t confusing at all 
In order to get to the facts, at this point I pursued a more purist chemistry route (clearly I was losing the will to live) and found that the pH of salty water is neutral at pH 7. So not acidic or alkali in its own right, does the neutral salt water wash affect mouth pH at all?
Saliva surfaces are thought to run at pH 7- neutral again, but when you eat, sugars in food are broken down into acidic compounds that create an acidic environment. This acidity is thought to favour the growth of certain acidic loving bacteria. It takes up to 20min for the saliva to re-neutralise the mouth after a meal. Saliva uses sodium and bicarbonate components to fight against the pH change, and literally wash away the acidic compounds.
Salt washes may quite simply aid saliva in flushing out the mouth, but perhaps the sodium in salt also plays a part. Contrary to the opposing internet claims, salt water doesn’t make the mouth acidic or alkali, it simply reduces the temporary acidity.
Final pinch of salt
You may have noticed me using the terms, perhaps and in theory a lot. It may have annoyed you, it certainly annoyed me. There just doesn’t seem to be a solid scientific source that plots out exactly how slightly salty water is antiseptic. I’ve had to draw presumptions from the information gathered from several sources, after ruling out some sources that clearly weren’t right.
The best I can cobble together is: salt water washes aid saliva in removing a temporary acidic environment and this together with a slight osmotic effect may reduce bacterial growth.
My take-home message is: check the internet claims you read are substantiated and align with some basic scientific principles.
NB Sea water is not anti-septic, so don’t go thinking you’ve got a nice clean wound after bathing in the sea.
Science FYI 