Why does it occur?
ummm… because it’s a wound?
It’s your bodys way of saying “hey, we got a crack in the hull. Watch it”
In the case of salt, I think it’s an osmotic thing; the water inside the exposed cells moves out toward the stronger salt solution, causing them to tend to collapse; fresh water can also cause a wound to sting because the osmotic gradient works the other way - water migrates into the cells, bloating them.
In theory, flushing a wound with a salt solution of similar concentration to your body’s own fluids shouldn’t hurt at all, except in that it might directly stimulate exposed nerve endings
Then how about alcohols? The only extraordinary property I can think of is their quick evaporation and drying action. Do alcohols work to dry out the cells, and does this account for the pain sensation?
I don’t know about alcohols, except that they very quickly kill micro organisms (presumably by interfering with some cellular function or other, or lots of them) - the pain in this case could be because cells are actually destroyed by the alcohol.
In all of the cases, I’d imagine it’s from exposed nerve cells dying (from the salt, alcohol, iodine).
I think alcohol can actually dissolve the lipid membrane around cells, meaning that it’s gonna kill exposed body cells as well.