How to Know the 18 Things You Should Never Put in the Dishwasher

Put wooden spoons, salad servers, and wooden cutting boards in the hand-wash pile. Heat and humidity can make wood swell, warp, or crack, and the University of Maine Extension cutting board guidance notes that some wood boards can separate in dishwashers. Wash wood with warm soapy water, rinse, and dry it right away.

Wash sharp chef's knives by hand so the blade does not get nicked, dulled, or knocked against other utensils. Hollow-handled knives are also risky because dishwasher heat can loosen the adhesive that holds some handles together, according to Whirlpool product guidance. Dry knives immediately before storing them safely.

Keep cast iron pans and carbon steel pans out of the dishwasher. Whirlpool's cookware care guidance says cast iron should be hand-washed to preserve seasoning, and carbon steel should avoid the dishwasher for the same reason. Clean both with hot water, a sponge or brush, and a prompt towel dry, then oil or season as your pan maker recommends.

Set aside nonstick pans and copper cookware before loading the racks. The American Heart Association recommends hand-washing nonstick skillets with soft sponges or cloths because dishwasher cleaning can damage the pan and may void a warranty. Copper can discolor or pit in the dishwasher, so wash it gently and dry it well.

Do not run disposable aluminum pans or tin items through a dishwasher. Whirlpool notes that throwaway aluminum can shift and leave black marks on dishes, while tin can rust in the dishwasher. Hand-wash these pieces only if they are meant to be reused, and recycle or discard single-use pans when appropriate.

Keep pewter, brass, bronze, and sterling silver or silver-plated pieces out unless the maker specifically says otherwise. Whirlpool's dishwasher-safe item guide warns that high water temperatures and detergent can discolor or pit pewter, brass, and bronze, and that silver can be damaged by contact with certain foods or stainless steel. Wash these pieces separately with a gentle cleaner made for the metal.

Hand-wash crystal, delicate glassware, and milk glass, especially if the pieces are old, thin, or sentimental. Whirlpool says delicate glass, hand-blown or painted glass, milk glass, and crystal may break, yellow, or etch in the dishwasher. Use a padded sink or basin, mild soap, and a soft towel to reduce bumps and chips.

Do not put antique china, hand-painted china, metal-rimmed china, or gold-colored flatware in a normal dishwasher load. GE Appliances warns that antique, metal-trimmed, hand-painted, and over-the-glaze patterns can fade or be damaged by high water temperature and detergent, even though some modern china may be dishwasher-safe. Treat decorated pieces as hand-wash-only unless their care instructions clearly say otherwise.

Leave thin or disposable plastics and insulated mugs or food containers out of the dishwasher. Plastic food-contact materials are made for specific uses, and the FDA explains that food-contact substances are reviewed for their intended use, so a flimsy takeout lid is not the same as a dishwasher-safe container. Whirlpool also notes that thin plastics can melt and that heat or water can damage the seal and insulation in travel mugs.