Why is it recommended to put salt on cuts?

A lot of bacteria, especially the ones in the mouth like Streptococci and some of the other mouth-dwelling organisms, are quite salt-sensitive.

For them, a big dose of salt is a bit like putting salt on a slug. It pulls the water out of the bacteria and dehydrates them, which can damage or disable them.

But some other bacteria, like Staphylococcus aureus, actually like salt; so if you have a wound on your finger it might not actually be so good for that because it will kill the bugs in there which are not Staphs, removing the competition for Staphylococci that are there; so you might end up with your wound being colonised entirely by Staph!

Overall, salt is quite good in very high concentrations because it stops a range of bugs growing, which is why meats and produce are salted to preserve them. But, the likelihood of you getting enough concentration of salt into a wound to kill the bugs is quite unlikely. It does have a soothing effect though, especially on mouth ulcers!

[This topic - on rubbing salt into a wound - has also been discussed on the Naked Scientists science forum]