A dishwasher is a modern miracle for saving time, but it is essentially a harsh environment: scalding hot water, powerful jets, and strong alkaline detergents. While it might be tempting to throw everything in there to avoid hand-washing, doing so can ruin your belongings, dull your dishes, or even start a fire.
Here are 8 things you should absolutely keep out of the dishwasher, and why:
1. Good Kitchen Knives
It seems logical to put knives in the cutlery basket, but the dishwasher is the sworn enemy of a sharp blade. The high heat and harsh detergent can warp wooden handles and cause micro-corrosion on the steel. Furthermore, the powerful water jets cause the knives to knock against other utensils, which dulls the edge.
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What to do instead: Hand wash and dry immediately.
2. Cast Iron Skillets
A well-seasoned cast iron pan is practically non-stick, but that “seasoning” is a thin layer of polymerized oil baked onto the surface. The harsh detergents in a dishwasher will strip that seasoning right off, and leaving the pan in the humid environment of a dishwasher will cause it to rust almost immediately.
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What to do instead: Rinse with hot water, scrub with a stiff brush (no soap), dry thoroughly, and rub with a light coat of oil.
3. Wooden Spoons, Cutting Boards, and Handles
Wood is porous. When exposed to the long, hot, steamy cycle of a dishwasher, wood absorbs water, causing it to swell and warp. As it dries, the wood fibers split, leading to deep cracks and splinters. The heat also strips the natural oils out of the wood, leaving it dull and brittle.
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What to do instead: Wash by hand with warm, soapy water and let air dry. Treat with food-grade mineral oil occasionally.
4. Insulated Travel Mugs and Tumblers (Yeti, Stanley, etc.)
Many insulated cups are made with a vacuum seal between two layers of metal. The intense heat of a dishwasher can cause the metal to expand, which can break that delicate vacuum seal. If the seal breaks, the cup loses its insulating ability. Additionally, the forceful water jets can get trapped between the outer shell and the inner liner, leading to rattling or mold growth.
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What to do instead: Hand wash the lid and cup with warm, soapy water.
5. Anything Copper, Aluminum, or Non-Anodized Metal
The alkaline chemicals in dishwasher detergent will tarnish, pit, and permanently discolor soft metals like copper, aluminum, and pewter. You will pull out a beautiful copper pot to find it covered in a dull, gray, chalky film that is incredibly difficult to remove.
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What to do instead: Hand wash gently and dry immediately with a soft cloth.
6. Fine Crystal and Hand-Blown Glassware
Fine crystal and delicate stemware can easily chip or shatter when rattled by the vibration and powerful water jets of a dishwasher. Furthermore, the extreme heat combined with the harsh detergent can cause “etching”—a permanent, cloudy film that cannot be washed off and ruins the sparkle of the glass.
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What to do instead: Hand wash in a sink with a rubber mat, using lukewarm water and a mild soap.
7. Non-Dishwasher-Safe Plastics (and single-use takeout containers)
Many lightweight plastics (like deli containers, cheap Tupperware, or takeout trays) are not designed to withstand the heating element at the bottom of a dishwasher. They will warp, melt, or leach chemicals. Even “dishwasher safe” plastics should be placed on the top rack, away from the heating element, to prevent melting.
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What to do instead: If it doesn’t explicitly say “dishwasher safe,” toss it or hand wash it.
8. Anything with a Paper Label (Like Wine Bottles or Jars)
If you try to repurpose a glass jar or put a bottle in the dishwasher with the label still on it, you are asking for a plumbing disaster. The hot water and steam will dissolve the paper and the glue. The paper turns to a thick pulp that can break off in chunks and clog the drain filter, spray arms, or the drain hose of your dishwasher.
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What to do instead: Soak the jar in hot, soapy water and scrub the label off by hand before putting it in the dishwasher.