The dishwasher is the hardest-working machine in most kitchens, and it takes a lot of abuse. Anything that fits on a rack tends to end up in there at the end of a long night, especially around the holidays. Appliance makers and repair experts say 7 kinds of cookware and tableware should be hand-washed instead.
The list below draws on Whirlpool’s own guidance on what is and is not dishwasher-safe, an expert Q&A with Whirlpool’s Institute of Home Science published on Today.com and a Chowhound guide by Stephen McPhee published April 29, 2025.
Cast Iron and Nonstick Pans
Thing number one: cast iron. Whirlpool says detergent and water strip the seasoning oils from cast iron, and heat chips enameled cast iron. Lucinda Ottusch, a dishwasher expert at the company’s Institute of Home Science, put it more bluntly in her Today.com Q&A, saying cast iron should never go in the dishwasher because the detergent strips its nonstick surface and invites rust. Chowhound’s guide agrees that dishwasher heat, pressure and detergent strip the seasoning and invite rust, adds that cast iron should never be soaked or left wet, and recommends hand washing with hot water and a non-abrasive sponge, then drying immediately.
Thing number two: nonstick pans. Whirlpool warns that the coating can be damaged or removed, and Chowhound says dishwasher heat and abrasive detergents break down the coating over time, and that ceramic coatings go faster than PTFE, the material known as Teflon. A soft sponge and warm soapy water cost nothing, and a good pan can last years longer. More cleanup shortcuts live in 20 clever kitchen tricks for home cooks.
Kitchen cleanups are a theme in 8 things never to store under the kitchen sink, and the machine itself needs care too, along with the disposal, as 8 things never to put in a garbage disposal before Thanksgiving cooking shows. The dishwasher also gets a rest on nights when cooks follow the routine in 11 traits of people who clean the kitchen before going to bed, as how to clean a dishwasher to reduce smells and dirt explains.
Wood, Knives and Insulated Mugs
Thing number three: wooden cutting boards and utensils. Whirlpool says heat and humidity can make wood swell, warp or crack. Chowhound explains that wood is porous, so soaking, heat and drying cycles cause swelling, splitting or warping, and it suggests a rub of food-safe mineral oil now and then.
Thing number four: sharp knives. Whirlpool says blades can nick or dull and can damage the rack. Chowhound calls knives especially vulnerable to the heat and salts used in dishwasher cycles, adding that jostling can cause microchips and moisture can damage wooden or composite handles. A dull knife makes dinner prep slower, and a good one is worth a minute or two at the sink after every use.
Thing number five: insulated mugs and travel mugs. Whirlpool says water and heat can damage the seal and insulation, which is why a mug that once kept coffee hot for hours suddenly doesn’t. Ottusch said insulated pitchers and drinkware belong on the same list because heat can damage the vacuum seal. Anyone with a favorite mug can read the care label first, and the pickup-and-wash routine in 8 things that don’t belong on a kitchen counter fits naturally after a hand wash.
For small kitchens that make hand-washing a chore, 8 best portable dishwashers compares machines, and organization ideas such as 16 kitchen organization ideas help give a drying rack a permanent home.
Delicate Glass and Aluminum
Thing number six: delicate glassware and crystal. Whirlpool says hand-blown, painted or milk glass and crystal can break, yellow or etch, which shows up as cloudiness or pitting from harsh detergent. Ottusch said lead crystal can become cloudy and pitted after repeated washings and that milk glass can turn yellow. Holiday glasses that appear once a year should go in the sink.
Thing number seven: aluminum cookware. Whirlpool says most aluminum pots and pans can discolor. Chowhound calls aluminum a reactive metal, saying dishwasher detergents can cause dark or cloudy spots, pitting or a chalky film, and Ottusch added that hot water can stain aluminum and detergent can dull the finish. Disposable aluminum pie pans can mark nearby items as they move around during the cycle.
Other Items That Do Not Belong in the Rack
The same sources name a few more items worth keeping out. Whirlpool lists thin or disposable plastic, which risks melting, and acrylic and melamine dishes, which can develop hairline cracks and fade. Ottusch’s list includes hand-painted ceramics, hollow-handled knives whose adhesive can melt, and pressure cooker lids, where food particles can lodge in valves.
Printed measuring cups are another item that surprises people. Ottusch said detergent can wear the measurement markings off, and items with paper labels can come loose and clog the drain.
A Thanksgiving Rule of Thumb
Thanksgiving falls on Nov. 26, when the dishwasher will run harder than at any other time of year. A tidy plan is to scrape big food pieces off plates before loading, which Ottusch recommended so scraps do not clog the drain, and to set aside a small tub for the special pans. For wooden spoons, a roasting pan and the good knives, that tub is the hand-wash pile. The reward is a dishwasher that handles the rest without a hitch.
Households that cook for crowds can pair this list with the other kitchen rules from earlier in the week. Together, those rules save a lot of repair calls.
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This article was produced with AI assistance and edited for accuracy against the sources linked above.