How to Know What Not to Put in a Dishwasher

Hand-wash wooden spoons, bowls, rolling pins, and most wooden or laminated cutting boards because dishwasher heat and moisture can make wood swell, warp, crack, or split. The USDA says some solid wood boards can be dishwasher safe, but laminated boards may crack and split, and University of Maine Extension recommends avoiding dishwashers for many wood and bamboo boards unless the maker says otherwise. Wash with hot, soapy water, rinse, and dry upright.

Do not put seasoned cast iron in the dishwasher because detergent and moisture can strip seasoning and encourage rust. Lodge, a cast iron maker, says a dishwasher will remove seasoning and likely cause rust. Clean cast iron with warm water, dry it completely, and apply a thin layer of oil when needed.

Keep chef's knives, paring knives, and other sharp prep knives out of the dishwasher unless you are following a specific maker's instructions. Wusthof recommends hand washing because high temperature and rubbing during the wash cycle can damage knives, while Whirlpool notes dishwasher loading can nick or dull sharp blades. Wash one knife at a time, dry it right away, and store it safely.

Most nonstick pots and pans last longer when washed by hand, even if some labels say dishwasher safe. Maytag says many nonstick finishes are fragile and that hand washing can help protect the coating for future use. Use a soft sponge, mild dish soap, and avoid abrasive scrubbers that can scratch the surface.

Crystal, hand-blown glass, painted glass, milk glass, and very thin wine glasses are better washed by hand. Whirlpool explains that delicate glassware can break, yellow, or develop etching that looks like cloudiness or pitting from harsh detergent. Wash these pieces gently, rinse well, and dry with a lint-free towel.

Do not risk heirloom plates, hand-painted ceramics, gold-rimmed cups, or antique china in a regular dishwasher cycle. Whirlpool says antique, hand-painted, and metal-rimmed china should be hand washed because high temperatures, detergent abrasion, and water pressure can cause breakage or fading. Treat sentimental or valuable pieces as hand-wash only.

Travel mugs, thermoses, and vacuum-insulated food jars can lose performance if heat and water damage the seal or insulation. Whirlpool lists insulated mugs and containers as not dishwasher safe because water and heat could damage the seal and insulation. Wash the inside with warm, soapy water and clean lids according to the maker's directions.

Only load plastic that is clearly marked dishwasher safe, and place heat-tolerant pieces on the top rack if the label says to. Maytag explains that tableware symbols are not universal and that you should check the care symbols before running an item through a wash cycle. Thin takeout containers, disposable lids, acrylic, and many unlabeled plastics can warp, melt, crack, or fade.