Muriatic or hydrochloric acid may corrode a stainless-steel surface. The chemical is often used to clean up after tile or concrete work, and if splashed onto a nearby stainless-steel surface, discoloration or rust can result. Concentrated soaps can leave a residue on stainless-steel surfaces, and the chemicals in the soaps can leave discoloration that may sometimes resemble rust. Cleaning products that contain chlorides can corrode a stainless-steel surface. This includes bleach and any cleaners that contain bleach in any amount, as well as bromides, iodides and thiocyanates, which can cause pitting and discoloration.
Salts contain chlorides, and like many chloride-based cleaners, may cause discoloration or corrosion of your stainless appliances. To prevent damage, avoid leaving any salty solutions or heavily salted foods in contact with your appliances for prolonged periods.
Water with a high iron content may leave a residue that resembles rust on your appliances, particularly if the water is in continuous contact with the stainless-steel surface. Steel wool and residue or dust from products that contain iron may corrode or leave a rusty discoloration on your stainless-steel appliance, as well.
Prolonged or continuous moisture between your stainless-steel appliance and another material, such as metal or a rubber mat, can lead to discoloration or even rust. For this reason, avoid setting wet objects on a stainless steel surface, and dry the surface thoroughly after cleaning.
Discoloration or corrosion of your stainless steel appliances should be addressed as soon as possible. Stains or rust marks left for long periods may be permanent. Often recently discolored stainless steel can be restored to its original finish using a stainless-steel cleaner or a mild cleanser and a nonmetal scrubbing pad. When finished, rinse your appliance thoroughly with water and dry. If you'd rather use a more natural cleaner, try a paste of baking soda and water. This will also clean away many discolorations. Rinse thoroughly when you finish cleaning, and dry completely.