There’s something satisfying about tossing dirty dishes into a machine and letting it work its soapy magic while you catch up on your favorite series or sip some chai. But not every kitchen item is meant to ride the dishwasher’s whirlpool.
While modern dishwashers are designed to handle most everyday kitchenware, certain items require special care to maintain their quality, functionality, and appearance. Understanding which items should stay out of your dishwasher isn’t just about preserving their condition—it’s about protecting your investments, ensuring food safety, and maintaining the efficiency of your appliance.
To that effect, here are 15 dishwashers’ “no-go’s” that’ll help you avoid costly replacements and keep your favorite tools in peak condition.
Wooden Cutting Boards or Utensils

Wood loves to expand and contract when subjected to heat and moisture, which makes the intense environment of a dishwasher especially problematic. When subjected to prolonged hot water, steam, and harsh detergent, the wood continually takes on water, then rapidly dries during the heated drying cycle. This repeated cycle of expansion and contraction can lead to serious warping, cracks, and splits overtime, and we like are wooden utensils in one piece, not in splinters.
Cast-Iron Cookware

Nothing ruins a seasoned cast iron pan faster than a trip through the dishwasher. One cycle will strip that carefully built-up oil coating, leaving the surface prone to rust. A quick hand wash with minimal soap keeps cast iron in pristine, heirloom-worthy condition.
Copper Cookware

Copper’s glossy finish comes from its reactive surface, so it’s highly vulnerable to the harsh detergents, high temperatures, and excessive moisture inside a dishwasher2710. Over time, these factors can dull the metal and cause dark spots or tarnish to appear. Handwashing copper cookware with mild soap and warm water preserves its signature gleam. If stubborn residue sticks, allow the pan to soak briefly and then use a soft sponge—never an abrasive pad—to avoid scratching. Thorough drying prevents water spots and keeps the metal’s luster intact.
Sharp Knives

A good knife is an investment—don’t let the dishwasher chip away at it (literally). The tumbling action can dull, or nick blades and detergents can damage handles. A quick rinse and a gentle wipe are all a quality knife needs to stay sharp.
Crystal Glassware

Crystal being more delicate than regular glassware is especially prone to clouding, chipping, or cracking in a dishwasher. The harsh detergents can chemically etch the surface, and the high heat plus turbulent jets of water can lead to physical damage. Many crystal pieces contain lead or other additives, which makes them softer and more easily prone to being scratched or fogged, potentially resulting in a permanent dull finish. If you adore that brilliant sparkle, keep your crystal collection away from the dishwasher’s spin cycle.
Nonstick Pans (If Not Labeled Dishwasher Safe)

Harsh dishwasher detergents can eat away at the delicate nonstick surface over time, leading to flaking and forcing you to replace them sooner. When in doubt, stick to a soft sponge and a bit of elbow grease.
Insulated Mugs

The vacuum seal in many insulated tumblers can be compromised by dishwasher cleaning as the high temperatures and water pressure in dishwashers can damage or weaken the seals that maintain the vacuum insulation. If the seal breaks, air can enter the space between walls, significantly reducing the tumbler’s insulation effectiveness. Once that happens, your trusty travel mug won’t keep coffee hot for nearly as long. A thorough hand scrub is best.
Pewter, Brass, and Bronze

Toss these metals into the dishwasher, and you’re likely to see it develop pitting or white spots, become tarnished, blackened, discolored and take on a generally dull appearance overtime. They’re better suited to gentle handwashing and an immediate towel-dry to maintain their shine.
Delicate or Vintage China

Family heirlooms or delicate porcelain, especially older pieces with gold or silver trim, can easily lose decorative details or crack under the intense spray and high heat of a dishwasher. If the china is more than 15–20 years old—or if it’s hand painted or features metallic designs—it’s safer to handwash to protect both the fragile surface and designs. A quick soak in warm water and gentle soap and a soft cloth gets them clean without the heartbreak.
Aluminum Cookware

Uncoated aluminum can darken and become dull in the dishwasher, and it may even leave marks on other items if it oxidizes during the wash cycle. Handwashing with mild detergent is what best preserves its surface.
Painted Glassware

Painted or printed designs on glassware—whether professionally finished or hand-decorated—can degrade in the dishwasher due to abrasive detergents, hot water, and strong spray jets. Even heat-set paints can fade or peel under repeated cycles of high temperatures. Although specialized acrylic enamel paints can be made dishwasher-safe if they’re properly oven-cured, you should still confirm the manufacturer’s guidelines or opt for handwashing if the glass is important or irreplaceable. Taking this extra care helps preserve vibrant colors and delicate details for years to come.
Items with Paper Labels

Paper labels tend to peel off mid-cycle, sticking to other cookware and clogging the filter. If you’re repurposing a jam jar or pickle jar, remove the label and adhesive by hand first.
Sifters, Sieves, and Graters

While many of these tools have small holes and intricate edges where food particles can stubbornly cling, making them challenging for dishwashers to clean thoroughly, some modern versions are specifically designed to be dishwasher-safe. However, for traditional models, a targeted hand rinse or soft-bristle scrub remains the best way to prevent trapped food residue. Always check the manufacturer’s recommendations, as newer designs may feature special construction that prevents food from getting lodged in rim seams or mesh.
Disposable Plastic or Thin Plastic Containers

Lightweight plastic containers can warp, melt, or even flip over in the heat and strong water spray of a dishwasher. Although some containers may be labeled “dishwasher-safe,” when in doubt, it’s best to either handwash them or place them on the top rack of the dishwasher with the “no heated dry” setting.
Food Items (Fish, Potatoes, and the Like)

Cooking fish or washing potatoes in the dishwasher might sound like a quirky online trend – one that’s been around since Vincent Price demonstrated it on TV in 1975 and continues to resurface on social media. However, it’s neither safe nor particularly efficient. Dishwashers don’t maintain the consistent temperatures needed for safe cooking, and detergent residue can end up right on your food. Best to keep culinary experiments out of the dish rack.