The dishwasher might be the most underrated appliance in your house. You load it, you press a button, and an hour later your dirty plates look brand new. So it makes sense that we get a little cocky and start tossing in anything that fits. Big mistake. Some stuff comes out warped, dull, rusted, or just flat-out ruined, and a few items can actually wreck the machine itself. Here’s what should never go anywhere near those spinning arms, and why.
Cast Iron Skillets
This one is the big one. If you take nothing else away, remember that cast iron and dishwashers are sworn enemies. That slick, nonstick surface you spent months building up? It comes from layers of oil baked into the metal, and one trip through the dishwasher strips all of it away in minutes. Then the pan sits there soaking wet with nothing to protect it, and it comes out covered in orange rust.
Lodge, the company that’s been making these pans forever, says flat out that a dishwasher will remove the seasoning and probably cause rust. If you do mess one up, all is not lost. You coat it in a thin layer of oil, flip it upside down in a 500-degree oven for about an hour, and rebuild the seasoning from scratch. Just rinse it by hand next time and dry it right away.
Your Good Knives
People throw knives in the dishwasher all the time and have no idea they’re slowly destroying them. During a cycle, the blades shift and rattle as water blasts them from every direction. Each time the edge bumps a rack or another fork, it chips a tiny bit. Over one full wash, that adds up to hundreds of tiny impacts on the part of the knife you actually use.
It gets worse. Heat and moisture loosen the rivets and pins holding the handle to the blade, and wooden handles swell up and crack. Wusthof tells customers straight up: do not put knives in the dishwasher. Henckels says most of theirs technically survive but they still don’t recommend it. Even brands that label knives “dishwasher safe” really mean the knife won’t fall apart, not that it’s a good idea. Hand washing takes about 30 seconds.
Wooden Spoons And Cutting Boards
Wood is basically a sponge that pretends to be solid. Soak it in hot water and harsh detergent for an hour and it does exactly what you’d expect: it swells, it warps, and eventually it cracks. The detergent also strips out the natural oils that keep the wood from drying out and splitting in the first place.
That goes for your trusty stirring spoons, salad bowls, and especially those nice butcher block cutting boards that cost real money. Wash them by hand with mild soap, towel them off, and let them air dry standing up. One tip a lot of people miss: don’t let wooden stuff soak in the sink either. Sitting in a pool of water does almost as much damage as the dishwasher does.
Nonstick Pans
The whole point of a nonstick pan is the coating. The heat and water pressure inside a dishwasher slowly break that coating down, and once it starts flaking off, your eggs go right back to sticking. At that point you’ve got a pan that does nothing special and may need to be replaced.
And yes, this includes the trendy ceramic pans everyone bought during the pandemic. Unless the manufacturer specifically prints “dishwasher safe” on the box, assume it isn’t. Even when it does say that, a soft sponge and warm soapy water will keep the “non” in nonstick a whole lot longer. Air fryer baskets fall in this same bucket. Most are labeled dishwasher safe, but they’ve got a nonstick interior and a million little crevices where gross water hides.
Insulated Travel Mugs
Your Yeti, your Stanley, that gas station tumbler you’ve grown weirdly attached to. The thing that keeps your coffee hot for six hours is a vacuum seal sitting between the inner and outer walls. Dishwasher heat can break that seal, and once it goes, water sneaks into the gap and the mug loses its whole reason for existing. Now your coffee is lukewarm by 9 a.m.
Some newer models are actually built to handle the dishwasher, so check the bottom for a label. If it doesn’t say so, play it safe and wash it by hand with warm soapy water and let it air dry. A bottle brush gets the bottom without much effort.
Copper, Brass, Gold, And Other Pretty Metals
Those copper Moscow mule mugs look amazing right up until you run them through a cycle and they come out dull and discolored. Copper, brass, bronze, and pewter all react badly to high-temperature water and detergent. They tarnish, they pit, and they lose the shine that made you buy them. If a copper piece has a clear protective coat on it, the dishwasher will ruin that too, and there’s no real way to bring it back.
Gold-colored flatware discolors fast, and any heirloom silver, gold, or bronze will lose its gleaming finish over time. Aluminum pots technically survive, but the minerals in your water can leave spots and the harsh detergent fades shiny metal to dull gray after a single run. For tarnished copper, a little baking soda on a damp cloth shines it right back up.
Plastic Containers And Lids
Plastic is a gamble. Some of it holds up fine and some warps the second it gets near the heating element at the bottom of the machine. Clear plastic is the worst offender, going cloudy and scratched and brittle after enough cycles. Those flimsy takeout containers you’ve been rinsing and reusing? The heat can warp them and mess with the plastic itself, so they’re really meant to be tossed, not run through the wash.
If you want to keep plastic in the dishwasher, look for a “dishwasher safe” stamp and always put it on the top rack, as far from the bottom heating element as you can get it. That includes the lids, which warp just as easily as the containers and then never seal right again.
Cheese Graters And Zesters
Think of every little hole on a grater as a tiny knife. Run it through the dishwasher and the same thing that dulls your good chef’s knife dulls all those small blades, so it takes more muscle to grate the same block of cheddar. That’s the slow problem.
The gross problem is that the dishwasher can’t get into those tiny holes to wash out the bits of cheese stuck deep inside. The water stream just passes over them. So your grater comes out looking clean but it’s still got old cheese hiding in the crevices. A quick scrub by hand with a brush right after you use it, before the cheese dries into cement, is the move.
Measuring Cups With Printed Numbers
This one sneaks up on people. You’ve got a nice set of measuring cups or a glass measuring pitcher with the lines printed on the side. Dishwasher detergent slowly eats away at that printed paint, a little more with every wash, until one day you reach for it and realize you can’t read where a half cup ends. Now it’s just a cup-shaped object.
The same thing happens to acrylic dishware with patterns or designs printed on it, plus anything that’s been repaired with glue. Hot water and detergent dissolve adhesive, so a handle you carefully glued back on will pop right off. Even stickers and price tags break down and gum up the works.
Stuff That Wrecks The Machine Itself
Everything above is about saving your stuff. This last group is about saving your actual dishwasher. Greasy pans are tempting to just shove in dirty, but oil cools and solidifies in the pipes and causes real clogs in the drain. Coffee grounds are small and gritty enough to slip past the filter, pile up in the drain, and leave you with a funky smell.
Big food chunks like bones, eggshells, and seeds can jam the filter or damage the pump. And if a glass ever shatters in there, stop the cycle and pick out every shard, because even tiny pieces clog the drain or get stuck in the spray arms. Those plastic labels on jars peel off mid-wash and gum up the filter too. The fix for all of it is the same: scrape and rinse before you load.
None of this means you have to start hand washing everything like it’s 1955. The dishwasher is still the best deal in your kitchen. Just keep these items out of it, spend the extra two minutes at the sink, and your good knives, pans, and mugs will outlast pretty much everything else you own.
