Sounds more like a simple case of salt and water in sweat meeting a non-stainless ferrous material in the sgian, which combination in the presence of atmospheric oxygen yields oxidation, i.e. rust.

Nothing magical or physiologically abnormal going on here. Try lightly oiling your blades after each use or sharpening and keepint the inside of the shealth oiled as well to drive away the sweat and form a barrier of oil to seaprate the iron from the salt.