18 Things You Should Never Put in a Dishwasher

Wooden Spoons, Bowls, and Cutting Boards

The harshness of dishwasher detergents can strip the natural oils that keep wooden utensils and cutting boards from drying out. When those oils are stripped, the wood will begin to crack. 

Wooden items should be hand washed quickly with a mild detergent in warm water. Do not allow them to soak because that can cause the wood to swell and distort. If you feel the wood needs to be disinfected, use a mild solution of chlorine bleach and warm water—1/4 cup of bleach to 1/2 gallon of water.

As with wood, natural stones for pizza should also be hand washed to prevent cracking and damage from harsh detergents.

Kitchen Knives

Knives pack a triple no-no whammy in the dishwasher. First, the edges can nick the protective coating on racks and baskets causing rust to form. Secondly, those sharp edges are dangerous when unloading the dishwasher especially when kids are helping.

Finally, the harsh dishwasher detergent can dull edges and cause wooden handles to loosen and split. It's best to hand wash all types of kitchen knives.

Graters and Sieves

Any kitchen tool with sharp edges should not be placed in the dishwasher. Graters and sieves can nick the plastic coating on the racks and rust will begin to form. 

And if you crowd items with small holes into the dishwasher, it is nearly impossible for the water stream to remove all of the food particles. Again, hand wash for best results.

Cast Iron Cookware

Cast iron skillets and pans have been around for centuries and they can last nearly forever if they are cared for properly. To keep cast iron from rusting and food from sticking, it must be seasoned with oil. The oil penetrates the iron and leaves a near perfect cooking surface.

When the cast iron is placed in the dishwasher, the harsh detergent and excessive water strips away the oil and leaves the cast iron unusable. The seasoning process must be completely started over. This applies to cast iron pots and pans that have outer enamel coatings, as well.

Even if your pan is covered with black crud on the outside and you think the dishwasher is an easy way to get it clean, resist the urge. Use some old-fashioned elbow grease instead.

Aluminum Pans and Cookware

If you've ever put a shiny disposable aluminum pie plate in the dishwasher, you've seen what happens. It turns dull and darkens. 

The same thing can happen to your aluminum pots, pans, and baking sheets. If the aluminum has not been anodized, the harsh detergent can cause pitting and corrosion. You may also see white spots on the surface from the alkalinity of the dishwasher detergent. Even if the pan is labeled as "dishwasher safe," it's better to hand wash.

If you want to remove the discoloration and spots, make a paste of cream of tartar and warm water. Spread the paste over the pot and use some elbow grease—and remember to hand wash next time!

Copper Pans and Mugs

Copper pans and mugs for Moscow Mules are classic and beautiful but require extra effort to keep them shiny and bright. Don't make the task any harder by putting them in the dishwasher. The harsh chemicals in dishwasher detergent will immediately dull the finish and can be corrosive and cause the copper to pit.

Pitting is not going to be removed even with the best copper cleaner and elbow grease.

Pressure Cooker Lids

While a pressure cooker pot or instant pot inner container may go through a dishwasher cycle just fine, you should never put the pressure cooker lids in the dishwasher.

The lid contains the valves that control how well the cooker works. The action of a dishwasher can force small particles of food into the valves and vents and cause the cooker to malfunction (explode). The harsh chemicals can also damage the rubber or silicone seals of the lid.

Nonstick Pans

While many nonstick pans are labeled as dishwasher safe, the harsh detergents and excessively high drying temperatures can take a toll on the nonstick coating. If you choose to wash your pans in the dishwasher, skip the drying cycle and allow them to air dry.

At the first sign of damage to the surface, it's time for a new pan. When the nonstick surface is scratched, chipped or flaking, it can release dangerous toxins into the food.

Ceramic Pans and Cookware

Ceramic pans and cookware are popular for their non-stick cooking surface. The name is a bit of a misnomer because the entire pan is not made of ceramic; there is just a ceramic coating bonded to the metal of the cookware. A ceramic coating can be applied to cast iron, aluminum, copper, or stainless steel.

Always hand wash ceramic cookware. Dishwasher detergents can contain bleach and citric acids that are too harsh for the finish.

Acrylic or Melamine Dishes

Lightweight, non-breakable acrylic or melamine dishware is very popular due to the bright colors and patterns. Unfortunately, the high water and drying temperatures and harsh dishwasher detergents can ruin the dishes. After several washings, especially for cheaper sets, there can be hairline cracks and loss of color and design.

If you love them and want them to last, then hand wash.

Insulated Glasses, Tumblers, and Thermal Containers

Plastic and metal insulated cups, tumblers and containers are great for keeping hot things hot and cold things cold. Most are constructed with two layers of material with an airspace between the two. It's that airspace that provides the insulation.

While some containers are labeled as dishwasher safe, many are not. It is best to hand wash both plastic and metal insulated containers. If you decide to place one in the dishwasher, opt for the top rack and skip the high heat of the drying cycle that can cause the seal to break and water to enter the airspace.

To remove coffee stains from the interior of your travel mug, make a paste of baking soda and water. Use a soft brush or cloth to apply the paste and then "scrub" gently. Rinse well and dry with a soft cloth.

Printed or Hand Painted Glassware

The techniques for commercial printing on glassware have improved but they are not always infallible in the dishwasher. That harsh detergent and the force of the water spray can remove the paint in just one or two washes.

And what good is a glass measuring cup with no lines?

Hand-painted glassware, even if the glass has been fired with heat, should never be placed in the dishwasher.

Thin Plastic Containers

If you save every butter tub and deli container to use for storage, be prepared to lose a few if you place them in the dishwasher. The high heat can cause them to melt or warp.

When you place them in the dishwasher, use the top rack only and skip the high heat drying cycle. Remove from the dishwasher to air dry.

Containers With Paper Labels

Along with your deli containers, you may also save glass food jars for storage. There's no problem with placing the jars in the dishwasher if you remove the paper labels first. If you don't, the paper and adhesive may come off and clog the dishwasher drain and food disposal system.

Extra tip: One of the best label/adhesive removers on the market is Un-Du, with a built-in scraper. 

Gold Flatware and Metallic-Trimmed China

While sterling silver flatware travels through a dishwasher well, gold-colored flatware will dull and discolor in the dishwasher due to the harsh detergent.

Porcelain and fine china are dishwasher safe unless they have gold metallic trim or images. The harsh detergent and the strong water action of the jets can cause the metallic work to flake away. With any delicate china, take care when loading so that pieces don't knock together and cause chipping.

Vintage China, Delicate Crystal, and Repaired Items

For any glass or china heirlooms, skip the dishwasher and carefully hand wash. This is especially important for any item that has been repaired. The high heat and harsh detergents will cause the adhesives used to weaken and you may lose any small pieces.

Delicate crystal should be hand washed to prevent chipping. If you decide to use the dishwasher, use the top rack and place the glasses between the tines, not over them, to help avoid breakage. Remember, some lead crystal will become cloudy and pitted after being etched by the harsh detergents.

Sterling Silver Knives

Sterling silver flatware goes through a dishwasher just as well as stainless steel, with one exception: Many sterling silver knives have a hollow handle and the heat of the dishwasher can cause the glue that holds the blade to the handle to melt and separate. This happens whether the blade is sterling or stainless steel. Hand wash instead.

Milk Glass

Milk glass dishware, especially vintage milk glass, can turn yellow after several washings in the dishwasher thanks to the high heat and harsh detergent. Hand wash the pieces to keep them looking their best.