Smarter: Things You Should Never Put in the Dishwasher

Cast-iron cookware. You risk removing the seasoning—the baked-on oil in your pan that helps prevent food from sticking—which can cause the pan to rust. 

Insulated mugs. Unless it’s labeled as dishwasher-safe, water can get inside the seal between the inner and outer layers of the mug, which might affect the mug’s ability to retain heat or keep drinks cold.

Nonstick pans. If the manufacturer doesn’t say it’s dishwasher-safe, avoid putting these in the dishwasher because it could wear away the coating, Larry says.

Sharp knives. Even if they’re labeled dishwasher-safe, you should wash them by hand because the knives can get dull after rubbing against other cutlery in the basket.

Tin. It will rust if washed in the dishwasher, so you should hand-wash and dry immediately. 

Wood. Water and heat can result in your wooden salad bowls or cutting boards warping and cracking.

The things that are generally safe, but with caveats …

Aluminum. It’s usually dishwasher-safe, but minerals in the water might cause spots or darkening. If you want to remove those, scour with a soap-filled steel wool pad.

China, crystal, and stoneware. It’s mostly safe, but if the pieces are hand-painted or fragile, wash by hand. And if it has gold leaf, that might discolor or fade in the dishwasher, Larry says.

Glass. Milk glass material might yellow after repeated washings in the dishwasher.

Plastic. Plastic items vary in their ability to withstand heat and detergents, so check whether it’s dishwasher-safe and make sure to place it on the top rack—away from the heating element—and don’t select cycles that use higher wash or dry temperatures.

Stainless steel and silver. They’re generally safe, but make sure you run your rinse cycle if not washing immediately because prolonged contact with food might damage their finish.

Bonus link: This is how we test dishwashers to see how good they are at removing food.