The list of items that should stay out of the dishwasher is short, and they share three vulnerabilities: high heat, prolonged contact with water, and the abrasive action of dishwasher detergent. Cast-iron pans, wooden utensils, sharp knives, nonstick pans, copper and aluminum cookware, fine crystal, and hand-painted porcelain top the list. Nearly everything else can go in the dishwasher. When in doubt about an item, hand-washing is the safer bet.
A cast-iron pan stays nonstick and resists rust thanks to its thin layer of seasoning. Dishwasher detergent is made to break down grease and strips that layer away in the first wash; the prolonged dampness that follows can cause the pan to rust within a few hours. The same principle applies to carbon-steel pans. Copper cookware can tarnish and spot in the dishwasher, while aluminum can react with the detergent and come out with a dull, dark-gray surface; this discoloration is irreversible. Hand-wash all three with warm, soapy water and dry them right away.
When wooden spoons, spatulas, and cutting boards sit in hot water for a long time, their fibers swell; as they dry, they shrink. This cycle can create cracks and splinters, which can trap food residue and odors. Knives have two separate problems: their edges can dull when they knock against other items in the machine, and detergent can gradually dull the steel surface. On knives with wooden handles, the handle can also loosen. Wash a good knife and dry it right away; every dishwasher cycle shortens its life a little. Graters and sharp-bladed choppers belong in the same group: they can dull in the machine and put the person unloading the rack at risk.
Nonstick pans last much longer when hand-washed, even if their manufacturer says they are dishwasher-safe; the machine’s heat and detergent gradually wear down the coating. Plastic containers without a mark showing they are heat-resistant should not go on the bottom rack, which is close to the heating element and can warp the plastic. Fine crystal glasses can turn cloudy and become scratched in the dishwasher, while patterns on hand-painted or gold-trimmed porcelain can wear away. If water gets between the two walls of a thermos or vacuum-insulated tumbler, its insulation can be permanently damaged. Water can also seep into glued or hollow handles and loosen them.
Most other items are usually fine: stainless-steel pots and flatware, heat-resistant glass, glazed ceramic, silicone molds, and labeled plastics. Loading them properly matters too: angle containers with their openings facing down, or water can collect inside and leave them wet at the end of the cycle. Arrange large pots so they do not block water from reaching smaller items. If you are unsure about an item, check the symbol on its bottom; if it does not have a dishwasher-safe symbol, wash it by hand.
A Note for Readers
This content is for informational purposes only and is not a substitute for medical advice. Consult your doctor before making any decision about your health.