Can a Dishwasher Ruin Your Knife? The Truth About Knife Cleaning

Many home cooks wonder if it’s safe to toss kitchen knives into the dishwasher. The short answer: Yes, a dishwasher can ruin your knife. High heat, harsh detergent, and jostling during the cycle can dull blades, promote corrosion, and even damage handles. Understanding these risks helps you choose the best cleaning method.

Why the Dishwasher Can Damage Knives

Abrasive Effects: Dishwasher detergents often contain bleaching agents or salts (like sodium silicate) that are too harsh for knife steel. These chemicals can etch and dull the cutting edge over time. In fact, detergents can make the steel “porous and blunt,” gradually removing sharpness. Knives thrown loosely into the rack may also bang into other utensils and hard surfaces, chipping or rolling the edge. In worst cases, a knife hitting a metal rack or the door can damage its point or tip.

Corrosion: Many kitchen knives are made of high-carbon or stainless steel. While “stainless” steel is corrosion-resistant, it is not immune to rust. The hot, humid, and alkaline environment inside a dishwasher is perfect for rust. Tiny pits or carbon content in the steel can react with detergent, causing specks of rust to form on the blade. Even handles aren’t safe: wooden or composite handles can absorb moisture, causing wood to swell, crack or the lamination to delaminate. As Villeroy & Boch notes, dishwasher heat and moisture can make wooden handles “swell and become brittle,” even splintering.

Handle Loosening: Repeated exposure to water and heat can weaken the glue and rivets holding a knife together. Wooden handles may warp, and plastic handles can crack. After many cycles, you might notice a loose or wobbly handle (dangerous for safety).

In short, the dishwasher’s combination of abrading chemicals, high heat, and moisture actively works against a knife’s materials, hurting edge and structure.

Hand Washing vs Dishwasher: Sharpness and Safety

Hand Washing (Recommended): The best practice is to wash knives by hand immediately after use. Use warm water, mild dish soap, and a soft sponge or cloth. This gentle approach cleans food residue without prolonged chemical exposure. Critically, hand-washing avoids banging and detergent blast. After rinsing, dry the knife thoroughly with a towel to prevent any moisture-induced rust. Proper hand-washing preserves edge sharpness and prevents corrosion much more effectively than the dishwasher.

Dishwasher (Discouraged): Putting knives in the dishwasher—even if labeled “dishwasher safe”—invites dulling. According to the makers of fine knives, “A dishwasher can be detrimental to the quality of your knife,” causing abrasion and corrosion. The detergent pods often contain gritty materials (like sand-like silicates) that act like a mild sandblasting on a blade. Even stainless blades gradually become “dull” under such conditions. For safety, also consider that a sharp blade in the utensil basket can cut your hand or damage the dishwasher’s interior coatings.

Cleaning Method	Sharpness Impact	Corrosion Risk	Handle Risk
Hand Wash	Maintains edge (no detergent abrasion)	Low (dry immediately to avoid rust)	Low (gentle warm water)
Dishwasher	Dulls edge (detergent chemicals, collisions)	High (extended moisture and harsh detergents)	High (wood swells, epoxy loosens)

Best Practices for Cleaning Knives

To keep knives sharp and safe, follow these best practices:

• Wash Promptly: Rinse or wash knives immediately after use to prevent food from drying on the blade. Dried-on food requires more scrubbing, which risks scratching the metal.
• Hand Wash with Care: Gently scrub the blade with mild soap and a sponge. Always hold the blade away from you – wipe from spine to edge or wrap the sponge around the spine. Don’t leave knives soaking, as prolonged moisture causes rust and can lead to slips or injury.
• Dry Immediately: After washing, dry every knife by hand. Water left on the blade will invite rust spots, even on stainless steel. A soft towel is ideal; towel-drying is “the best way to keep rust at bay”.
• Store Safely: Store knives in a block, on a magnetic strip, or in a sheathed knife roll. Avoid tossing them loose in a drawer where edges can knock into other utensils and dull. Proper storage helps keep blades sharp longer.
• Use Smooth Surfaces: When cooking, use a wood or plastic cutting board (not glass or stone) as your surface; hard surfaces chip edges. This complements your cleaning routine by reducing wear.

By consistently washing by hand and immediately drying, you “keep knives sharp” and extend their life. Dishwasher-safe claims (often used for convenience) are misleading – even dishwasher-safe materials (like certain plastics) have limits on repeated exposure. When it comes to knives, the extra care of hand-washing pays off in performance and safety.

Still curious? Check out our Ultimate Guide to Knife Sharpening.

P.s. If you’re in Singapore and need professional sharpening, feel free to visit our knife sharpening service! We offer precision sharpening for all types of knives, ensuring your blades stay razor-sharp.