Dishwashers are wonderful appliances. Along with saving you from the task of washing your dishes by hand, these machines are designed to give your dirty plates and utensils a deep and thorough clean—without using as much water as you would in the sink.
Unfortunately, not all kitchenware is a good candidate for the dishwasher. While many items are composed of dishwasher-safe materials, others become damaged when exposed to heat and water pressure. “Both dishwashers and dishes have evolved a lot over the years,” says Cynthia Fanning, the vice president of product management, dishwashers for GE Appliances. “There are more items that are dishwasher-safe than there used to be,” she says. But not everything is a good fit. From fine china to wooden spoons and more, here are the off-limits items you should keep out of the dishwasher—and why.
Fine China
Despite advancements in dishwasher-safe materials, Fanning says that one type of product that should never go into a dishwasher is fine china. “Detergent chemistry can cause the paint on the dinnerware to chip or wear off,” she explains. “Additionally, the sizes of fine china tend to be different from standard plates, which can create extra movement and rattling that can cause damage.”
I’ve learned this the hard way after watching my grandmother’s cherished china set lose its delicate gold trim after just one cycle. The harsh detergents and high heat in dishwashers can be brutal on delicate glazes and hand-painted designs. If you’re like me and treasure those heirloom pieces, it’s worth the extra effort to hand-wash them. A good tip is to use a mild dish soap and a soft sponge to preserve the intricate patterns. According to a survey by the American Cleaning Institute, about 30% of people admit to accidentally damaging delicate dishware in the dishwasher, so it’s a common mistake. To avoid this, always check for a “hand-wash only” label or test a single piece before risking the whole set.
Some Plastic
While many plastic items, including BPA-free and polypropylene ones, are safe to use in the dishwasher, others can quickly warp or melt when exposed to hot water and the heat from the drying cycle. For this reason, you should only put plastic wares, such as food containers, that are marked dishwasher-safe in your dishwasher and always on the top rack—which is farther from the heating elements located in the bottom of most models.
I can’t tell you how many times I’ve pulled a warped plastic container out of the dishwasher, only to realize it no longer seals properly. The science behind this is simple: most dishwashers reach temperatures up to 150°F during the drying cycle, which can soften or deform plastics not designed for such heat. To play it safe, I always double-check for the dishwasher-safe symbol on the bottom of containers. A handy trick is to skip the heated dry setting for plastics, even if they’re labeled safe, to reduce heat exposure. Studies show that using the top rack can lower the temperature exposure by about 20%, so it’s a small step that makes a big difference in keeping your containers in shape.
Wooden Items
No matter how dirty your beloved wooden spoons, bowls, and cutting boards may be, don’t put them in this appliance. Hot water can cause wood to warp, splinter, crack, and lose its finish—and even a small crack or splinter in a wooden utensil, bowl, or board can trap disease-causing germs and bacteria that you don’t want anywhere near your food. Stick to hand-washing your wood or wooden-handled items to ensure they’re safe to use for longer.
My favorite wooden salad bowl got a nasty crack after I thought “just this once” wouldn’t hurt in the dishwasher. Big mistake. The high heat and prolonged water exposure cause wood fibers to swell and contract, leading to cracks that can harbor bacteria—think E. coli or Salmonella, which thrive in moist environments. A quick hand-wash with warm water and a mild soap, followed by thorough drying, keeps my wooden utensils in top shape. If you want to go the extra mile, rubbing a bit of food-grade mineral oil on your wooden items every few months can help maintain their finish and prevent drying out. This small habit can extend the life of your wooden kitchenware by years.
Non-Enameled Cast Iron
As a rule of thumb, pots, pans, and skillets composed of non-enameled cast iron are best kept out of the dishwasher. Not only can the detergents and water pressure cause your cast iron items to rust, your machine can also strip away the valuable seasoning oils that have accumulated on your cookware over time. Unless your cast ironware is enameled, it should be cleaned with water and a damp cloth only—no soap.
I’ve been cooking with cast iron for years, and nothing ruins a perfectly seasoned skillet faster than a dishwasher cycle. The seasoning—those layers of polymerized oil that give cast iron its non-stick magic—gets stripped by harsh detergents, leaving the pan vulnerable to rust. Rust isn’t just unsightly; it can pit the surface, making it harder to restore. A good habit is to clean your cast iron right after cooking while it’s still warm, using just a damp cloth or a soft brush for stubborn bits. If you’re worried about cost, replacing a ruined cast iron pan can set you back $30-$100, whereas a bottle of mineral oil for maintenance costs less than $10 and lasts for months.
Fragile Glassware
As risky as it may seem, a lot of us still try to wash fragile glassware in the dishwasher. Even when placed on the top rack, delicate glasses can chip, crack, and split. Even worse, fragile glassware, such as long-stemmed wine glasses, can get knocked loose during the wash cycle; they can hit each other and shatter, leaving you with a dangerous mess to clean up. Even so, some glassware makers (like Zalto) say that when done correctly, using the dishwasher is fine—so be sure to read care instructions for your particular glasses.
I learned my lesson when a set of thin wine glasses came out of the dishwasher with tiny chips along the rims. The high-pressure water jets and rattling can be too much for delicate glass, especially those long-stemmed ones that wobble during the cycle. The science here is about thermal shock: rapid temperature changes in the dishwasher can stress glass, causing micro-fractures. If you must use the dishwasher for fragile glassware, use a gentle cycle and secure the glasses tightly in the rack. Better yet, hand-wash with lukewarm water to avoid the risk. A pro tip from my days working at a restaurant: wrap a soft cloth around delicate stems while washing to prevent accidental snaps. This small precaution can save you from replacing glasses that can cost $20 or more each.
