In all parts of the world, colds and sore throats occur with predictable periodicity. Their relative harmlessness ensures that the lustful commercial gaze of Big Pharma stays focussed on solving life-threatening problems like erectile dysfunction.
Thus, the task of relieving sore throats falls squarely upon the time-tested shoulders of household remedies. In my family, like many others, the standard chemotherapeutic cocktail is salt water - plain and simple. My mom, a medical doctor, swears by gargling salt-water. If you eavesdrop what many people will only whisper, it is more than just a quick fix for a bad throat. It is elixir.
So why does it work? Is there is physico-chemical explanation?
There seem to be several explanations on the web, including many (such as a change in pH) which I cannot buy. The key concept here is osmosis. I try to describe that process next.
Normally, when you have an uneven concentration of something (solute, like ink) dissolved in water, the process off diffusion (which is the merely an avataar of the Second Law) drives the transport of the solute (in reality the solvent is also diffusing simultaneously) from regions of high concentration to regions of low concentration. It tries to even things out, spread stuff around, like Vladimir Lenin. Think about blood dropped into water, or the spreading of Lenin's fart.
When there are semipermeable walls separating the regions of high and low solute concentration, well, things change. Our friend Mr. Osmosis makes his theatrical debut. The big difference is the semipermeable membrane - it is impermeable to the solute, and permeable to the solvent. Now, nature is a socialist and likes evenness. Since the solute is jailed by the membrane, transport of the solvent will have to do.
Sounds complex. A practical demonstration is in order. When you drop a grape into a glass of water for sufficient time, you see osmosis at work. The grape swells up, because water flows across the grape skin (membrane) into the grape (crudely high concentration sugar solution).
The following diagram, which I stole from Wikipedia, demonstrates the same idea, only here I am changing the makeup of the neighborhood of the cell. Hypertonic means, the environment has high solute concentration compared to the cell. The rest of the picture is self-explanatory and I won't hurt your intelligence by spelling it out.
So now that we have learned some of the science behind the phenomenon, we can get back to the question of gargling. When you have a sore throat, often bacteria and swollen inflamed cells are the culprit. So when you gargle and create a hypertonic environment, the bacteria shrivel up, become emaciated, beg for mercy, and die.
At the same time, your swollen inflamed cells also lose water. But this is a good thing. Why? Because once you've eliminated the metabolites in the inflamed cells, your vasculature brings in fresh supplies and helps with the process of healing.