Why is my stainless steel discolouring?

Usually from one of a few common causes: heat tint, burnt-on grease, harsh or wrong cleaning, or chlorides. Heat tint - high heat causes stainless to develop tint colours (straw, blue, brown, rainbow) as the surface oxidises, common on cooking surfaces and around burners; usually cosmetic. Burnt-on grease and carbonised residue - grease and food that bakes on and carbonises leaves brown or black staining and dulls the surface, common on and around cooking equipment. Harsh or wrong cleaning - abrasive pads, wire wool or the wrong chemicals damage the surface and its protective passive layer, causing discolouration, scratching and dullness. Chlorides - salt, and chloride-based cleaners like bleach, can break down the protective layer and cause staining, pitting and rust spots (even on stainless). So stainless discolours from heat, grease, harsh/wrong cleaning, or chlorides - and the type of discolouration points to the cause (rainbow/blue = heat, brown/black = burnt grease, dull/scratched = abrasive cleaning, stains/rust spots = chlorides). Identifying the cause shows how to fix and prevent it. So it discolours from heat, grease, wrong cleaning or chlorides. This is general commentary.

That is heat tint - discolouration caused by high heat. When stainless steel is exposed to high heat, the surface oxidises and develops tint colours - straw or gold, then blue, then brown, and sometimes rainbow patterns - depending on the temperature reached. This is common on cooking surfaces, around burners and hot spots, on the backs of ranges, and on equipment exposed to high heat. Heat tint is usually cosmetic - a discolouration rather than damage - though it is a sign of the heat the surface has seen, and severe or repeated heat tint can, over time, affect the surface and its corrosion resistance. Heat tint can often be reduced or removed with appropriate stainless cleaning (stainless-safe cleaners, cleaning with the grain, not harsh abrasives), but it tends to recur where the heat continues (so it may come back on a surface that keeps getting hot). So the rainbow or blue marks are heat tint from high heat - usually cosmetic, removable with appropriate cleaning, but recurring where the heat does. This is general commentary.

Yes - harsh or wrong cleaning is a common, avoidable cause of stainless discolouration and damage. Abrasive pads, wire wool or harsh scourers scratch the surface (dulling it and creating fine scratches that trap dirt and can corrode), and wire wool in particular can leave particles of ordinary steel embedded in the surface that then rust, leaving rust spots on the stainless. The wrong chemicals - harsh acids or alkalis, or chloride-based products like bleach - can attack the surface and its protective passive layer, causing discolouration, etching and dullness and reducing corrosion resistance; and leaving some chemicals on too long, or not rinsing, can mark it. Ironically, over-aggressive cleaning (trying to get stainless bright) often damages and discolours it. So stainless needs cleaning with appropriate, stainless-safe products and methods - soft cloths, appropriate stainless cleaners or mild detergents, cleaning with the grain - not abrasives, wire wool or harsh/chloride chemicals. So yes - the wrong cleaning can damage stainless, so clean it correctly. This is general commentary; follow product guidance.

Usually from chlorides or from contamination with ordinary steel - stainless can rust in these situations despite being 'stainless'. Chlorides are stainless steel's main enemy: prolonged or concentrated contact with chlorides (from salt, and from chloride-based cleaners like bleach/sodium hypochlorite) can break down the protective passive layer locally and cause corrosion - staining, pitting and rust spots. So rust spots often come from bleach or chloride-based sanitisers left on the surface, or salt left in contact. The other common cause is contamination with ordinary (carbon) steel - contact with wire wool particles or carbon-steel tools can leave iron deposits on the stainless that then rust. To prevent and address: avoid prolonged chloride contact (rinse off salt and food residue, use bleach and chloride sanitisers appropriately - correct dilution, not left on, rinsed thoroughly - or use non-chloride stainless-safe cleaners), and avoid ordinary-steel contamination (no wire wool or carbon-steel tools on stainless). So rust spots on stainless usually mean chloride exposure (often bleach or salt) or steel contamination - both avoidable. This is general commentary; follow product and manufacturer guidance.

Bleach (chlorine bleach, sodium hypochlorite) contains chlorides, which are stainless steel's main enemy - so bleach left on stainless, used undiluted, or used too often can cause staining, pitting and rust. Stainless resists corrosion well but is vulnerable to chlorides: prolonged or concentrated chloride contact can break down the protective passive layer and cause corrosion. So while bleach can be used carefully in a kitchen, leaving it on stainless surfaces, using it undiluted, or using it frequently on stainless risks chloride attack - staining, pitting and rust spots. If bleach or chloride-based sanitisers are used on or near stainless, they should be used at the correct dilution, not left on the surface, and rinsed thoroughly afterwards. Better still, use stainless-safe, non-chloride cleaners and sanitisers on stainless where possible. So bleach is not ideal for stainless because of its chlorides - use it appropriately and rinse it off, or use non-chloride alternatives, to avoid chloride staining and corrosion. So yes - bleach can harm stainless if left on or overused; use it carefully or avoid it on stainless. This is general commentary; follow product guidance.

Clean it with appropriate, stainless-safe methods and products, remove burnt-on grease properly, avoid abrasives and chlorides, and keep it clean - which keeps it bright and its corrosion resistance intact. Use soft cloths, appropriate stainless cleaners or mild detergents, and clean with the grain of the steel - not abrasive pads, wire wool or harsh scourers (which scratch and can leave rusting steel particles). Remove burnt-on grease and carbonised residue with proper degreasing and cleaning (much stainless discolouration is burnt-on grease, especially on and around cooking equipment) - not by harsh scrubbing. Avoid chlorides: rinse off salt and food residue, and do not leave bleach or chloride-based cleaners on the surface (use them appropriately and rinse, or use non-chloride alternatives). Avoid ordinary-steel contamination (no wire wool or carbon-steel tools). And keep the surface clean generally, so grease does not bake on and build up. This keeps the stainless bright and its protective passive layer intact. A thorough deep clean removes built-up, burnt-on grease properly with appropriate methods. So clean with stainless-safe methods, remove grease properly, avoid abrasives and chlorides, and keep it clean. This is general commentary; follow manufacturer and product guidance.