system
Given the following post, respond as if you're commenting on Reddit:
human
Every time I have a scratchy or sore throat, I am told to gargle salt water. Why?

How does gargling salt water help your sore throat? Or does it even help?
gpt
Believe it or not, this is actually a treatment commonly used for the great-great-grandaddy of all chest colds, cystic fibrosis. In CF, people get thick, sticky mucus because of a defect in their ability to secrete water into the airways. 

Normally, you secrete mucins (the proteins that make snot snotty) along with signals that tell the cells lining your airway to secrete enough water to dilute the mucins to a usable viscosity and elasticity. Think flour and water; add just enough water to the flour and you have a thin gruel. Not enough water and you have bread dough. People with CF, however, lack an important bit of the machinery of that whole process, so they don't push out enough water. As a result the mucus is much thicker and, like bread dough, is much harder to pour. 

One treatment is hypertonic saline; a high concentration sodium chloride solution that is put in an inhaler and breathed in as an aerosol. The aerosol particles sit on top of the mucus and this sets up an osmotic gradient that pulls water up from the epithelial cells to dilute the mucus. Bread dough becomes gruel again, for a short time.

Gargling salt water makes a poor-mans aerosol; bubbling air up through the water makes little salt water droplets that can float down into your airway. The osmotic gradient that forms when they land acts to pull water out into the airway. This water mixes with the mucus that may have solidifed somewhat around some irritant (be it bacterial, botanical, or whatever) and helps you flush it away.