8 Things You Absolutely Should Not Put in a Dishwasher (And Why)

8 Things You Absolutely Should Not Put in a Dishwasher may sound like an overly cautious kitchen rule, but the wrong wash cycle can permanently damage cookware, utensils, drinkware, and delicate dishes. A dishwasher uses hot water, powerful detergent, spray pressure, and prolonged moisture. While everyday plates and glasses usually handle those conditions well, many specialty kitchen items cannot.

Sharp knives can lose their edges. Wood can swell and crack. Cast iron can rust. Copper can discolor. Meanwhile, delicate china and crystal may chip, fade, or become cloudy. Even something as harmless as a jar with a paper label can create trouble if pieces of adhesive or paper enter your dishwasher’s filter or pump.

That does not mean you need to fear your dishwasher. Instead, you simply need to know which items belong at the sink. Whirlpool specifically recommends hand washing kitchen knives, fine china, crystal, wooden items, cast iron, and many types of nonstick cookware. It also advises checking manufacturer instructions whenever you feel unsure.

I learned this lesson after putting a favorite wooden spoon and a good kitchen knife through several dishwasher cycles because cleaning them that way seemed easier. The spoon gradually became rough around the edges, while the knife stopped cutting as cleanly as it once had. At first, I blamed ordinary wear. However, I eventually checked the care instructions and discovered that both pieces should have stayed out of the dishwasher. Since then, I have kept a small hand-wash area beside the sink for delicate kitchen tools. It takes only a few extra minutes, yet those items now stay in much better condition.

If you want your cookware, utensils, and special dishes to last, these 8 Things You Absolutely Should Not Put in a Dishwasher deserve a place on your kitchen-care checklist.

Sharp Knives and Wooden Kitchen Tools

1. Sharp Kitchen Knives

High-quality kitchen knives sit near the top of the 8 Things You Absolutely Should Not Put in a Dishwasher because a dishwasher creates several problems at once.

First, the blade can strike racks, utensils, or other dishes during the cycle. Those repeated contacts can nick or dull a finely sharpened cutting edge. Whirlpool specifically warns that sharp knife blades can become nicked or dull in a dishwasher and may even damage dishwasher racks.

Additionally, some knives contain handles made from wood or other materials that react poorly to heat and moisture. Hollow-handle knives can present another concern because manufacturers may use adhesives to attach the handles, and repeated dishwasher exposure can weaken those bonds. Whirlpool’s product guidance specifically notes that adhesives used in some hollow-handle knives may loosen during dishwasher washing.

Instead, wash a sharp knife soon after you finish using it.

Use warm water, mild dish soap, and a soft sponge. Keep the sharp edge pointed away from your hand while cleaning. Then, rinse the blade and dry the knife immediately.

Do not leave good knives soaking in a sink, either. Prolonged moisture can affect certain blade materials and handles.

Hand washing also improves safety. When you place a sharp knife among plates and utensils, another person may reach into the dishwasher without seeing the exposed blade.

Therefore, the few seconds you save with machine washing rarely justify the potential damage.

Among the 8 Things You Absolutely Should Not Put in a Dishwasher, expensive or frequently used kitchen knives may benefit the most from this simple habit.

2. Wooden Spoons, Cutting Boards, and Utensils

Wood looks durable, but it behaves differently from glass, stainless steel, or ceramic when exposed to repeated heat and moisture.

That makes wooden spoons, cutting boards, salad servers, and wood-handled utensils another important entry among the 8 Things You Absolutely Should Not Put in a Dishwasher.

During a dishwasher cycle, wood absorbs moisture. Then, heat accelerates drying. Repeating that wet-and-dry cycle can cause the wood to swell, warp, split, crack, or lose its finish.

Whirlpool specifically advises washing wooden ware by hand because untreated wood can warp, crack, or lose its finish. Its dishwasher guidance also notes that high heat and humidity can make wooden cutting boards and utensil handles swell, warp, or crack.

Fortunately, wooden kitchen tools require very little special care.

Wash them with warm water and mild dish soap. Use a sponge or soft dish brush to remove food residue. Next, rinse them thoroughly and dry them with a clean towel.

Afterward, allow them to air-dry completely before storing them in a drawer or cabinet.

For unfinished wooden cutting boards and utensils, occasional treatment with a food-safe oil approved for that purpose may help maintain the surface. However, always follow the item’s care instructions.

You should also avoid soaking wooden tools for long periods. A sink filled with water can create many of the same moisture problems as a dishwasher.

With gentle cleaning, a good wooden spoon or cutting board can remain useful for years.

So, when loading the machine after dinner, remember that wood earns its place among the 8 Things You Absolutely Should Not Put in a Dishwasher.

Cast Iron and Delicate Cookware

3. Cast-Iron Pans and Skillets

A seasoned cast-iron skillet develops its useful cooking surface through layers of polymerized oil. A dishwasher works against that seasoning.

For that reason, cast iron ranks among the most important 8 Things You Absolutely Should Not Put in a Dishwasher.

Dishwasher detergent, extended water exposure, and the wash cycle can strip seasoning from the pan. Once the protective layer disappears, bare iron becomes much more vulnerable to rust.

Whirlpool specifically states that dishwasher washing can remove the necessary oils from cast iron. Its product guidance also warns that cast-iron seasoning can be removed and the metal may rust.

Instead, clean cast iron by hand.

Allow the skillet to cool enough to handle safely. Then, use warm water and a brush, scraper, or other cleaning tool recommended by the cookware manufacturer.

For stubborn food, follow your pan manufacturer’s instructions rather than reaching automatically for harsh chemicals.

After washing, dry cast iron thoroughly and promptly. Moisture left on the surface encourages rust.

Many cast-iron owners also apply a very thin layer of cooking oil after drying, depending on the manufacturer’s maintenance recommendations.

Enameled cast iron needs different care because enamel protects the iron underneath. Nevertheless, some manufacturers still recommend hand washing certain pieces to preserve their appearance and finish. Therefore, check the individual product instructions rather than assuming every enameled pan belongs in the dishwasher.

Cast iron can last for generations when maintained correctly. However, one aggressive cleaning habit can create unnecessary work.

Therefore, keep your favorite skillet out of the machine and remember why cast iron appears among the 8 Things You Absolutely Should Not Put in a Dishwasher.

4. Nonstick Cookware Unless the Manufacturer Approves It

Nonstick cookware requires a little more nuance.

Some modern nonstick pans carry dishwasher-safe labels. Others do not. Even when a product technically allows machine washing, the manufacturer may recommend hand washing to maintain its appearance or coating.

Therefore, nonstick cookware belongs on the 8 Things You Absolutely Should Not Put in a Dishwasher list whenever its care instructions recommend hand washing.

Whirlpool advises that high water pressure, heat, and detergent can damage or remove some nonstick coatings and generally lists nonstick cookware among items better suited to hand washing.

Instead, let the pan cool before washing it.

Then, use warm water, mild dish soap, and a soft sponge. Avoid abrasive pads unless the manufacturer specifically approves them because aggressive scrubbing can damage some cooking surfaces.

Also, avoid stacking sharp objects directly against the coating during storage.

Manufacturer instructions matter especially with nonstick cookware because materials and construction vary substantially between products. A pan labeled dishwasher-safe should receive different treatment from a pan labeled hand-wash only.

That same principle applies throughout this entire guide.

When you see a dishwasher-safe symbol, follow it. When you see “hand wash only,” believe it.

After all, replacing a pan because its coating deteriorated early costs more time and money than spending a minute washing it at the sink.

Consequently, treating sensitive nonstick cookware as one of the 8 Things You Absolutely Should Not Put in a Dishwasher can help preserve its cooking performance and appearance.

Fine China, Crystal, and Special Metals

5. Antique China, Hand-Painted Dishes, and Crystal

Everyday ceramic dinnerware often handles dishwasher cycles without difficulty. However, delicate heirloom dishes require much more care.

Fine china, antique plates, hand-painted dishes, gold-trimmed dinnerware, and delicate crystal belong among the 8 Things You Absolutely Should Not Put in a Dishwasher, unless their manufacturers specifically state otherwise.

Whirlpool recommends hand washing fine china and crystal because dishwasher washing may damage their finish. Its dishwasher manuals also tell owners to check manufacturer recommendations before cleaning china or stoneware and warn that antique, hand-painted, or decorated pieces may require special treatment.

Dishwashers create several risks for delicate pieces.

First, dishes can vibrate or shift during washing. Therefore, a fragile rim may strike another object and chip.

Second, repeated exposure to strong detergent and heat may affect decorative finishes.

Finally, some delicate glassware may lose clarity or develop visible surface changes over time.

Hand washing gives you much greater control.

Place a folded towel or soft mat in the bottom of the sink when cleaning especially fragile pieces. Then, use lukewarm water, mild dish soap, and a soft cloth or sponge.

Wash one piece at a time. Rinse carefully, and avoid stacking delicate dishes while they remain wet.

If an item has significant monetary, historical, or sentimental value, consult its manufacturer or an appropriate restoration professional before using unfamiliar cleaning products.

The safest approach remains simple: when losing the item would genuinely upset you, do not experiment with an aggressive dishwasher cycle.

That rule alone explains why special china and crystal belong on any serious list of 8 Things You Absolutely Should Not Put in a Dishwasher.

6. Copper, Brass, Pewter, and Other Reactive Metals

Shiny copper cookware can become a dramatic focal point in a kitchen. Unfortunately, a dishwasher can quickly change its appearance.

Copper consequently joins the 8 Things You Absolutely Should Not Put in a Dishwasher, along with several other metals that can discolor, pit, or lose their finish.

Whirlpool recommends hand washing copper pots and mugs to avoid pitting and discoloration. It also warns that high water temperatures and detergent can discolor or pit materials such as pewter, brass, and bronze.

Bosch likewise identifies materials including cast iron, pewter, brass, tin, bronze, and some aluminum as unsuitable for dishwasher cleaning because of their sensitivity to dishwasher conditions.

For copper, use warm water, a mild dishwashing liquid, and a soft sponge for routine cleaning.

Dry the cookware promptly afterward.

If tarnish develops, use only a polishing or cleaning method appropriate for that specific product. Copper cookware may contain different linings and exterior finishes, so one cleaning product does not fit every piece.

You should take similar care with brass and other specialty metals.

Additionally, keep sterling silver, silver plate, and specialty metal flatware separated according to manufacturer recommendations. Different metals can react differently to detergents and prolonged moisture.

The important lesson here involves recognizing material rather than treating every metal as stainless steel.

A stainless-steel mixing bowl may perform perfectly in a dishwasher. A polished copper pot may not.

Therefore, before loading an expensive metal item, check its manufacturer’s care label.

That small step can prevent the discoloration and finish damage that place specialty metals among the 8 Things You Absolutely Should Not Put in a Dishwasher.

Labeled Containers and Insulated Drinkware

7. Jars, Bottles, and Containers With Adhesive Labels

A glass jar might seem completely dishwasher-safe. The glass itself often is. However, the paper label glued to its side creates a different problem.

Containers with labels therefore earn a surprisingly important place among the 8 Things You Absolutely Should Not Put in a Dishwasher.

During washing, hot water can loosen paper and adhesive. Pieces may separate from the container and move through the dishwasher.

Older Whirlpool dishwasher guidance specifically warns that glued labels can loosen from bottles and cans and clog spray arms or the pump, reducing wash performance.

Modern dishwashers also rely on filtration and drainage systems that work best when they remain clear of unwanted debris. Whirlpool notes that clogged filters and drains can contribute to dishwasher problems and odors.

Therefore, remove labels before putting reusable jars through a dishwasher.

Soak the jar in warm water first if necessary. Peel away as much paper as possible, then remove remaining adhesive using a method appropriate for the container material.

Once the jar is clean and you have confirmed that the container itself is dishwasher-safe, you can wash it according to the manufacturer’s instructions.

This precaution also applies to containers with stickers, price labels, decorative adhesive, or loose paper attached.

Do not assume the dishwasher will conveniently remove the label for you.

It may remove it, but the label still has to go somewhere.

Taking two minutes to strip a jar before loading it can prevent paper fragments from circulating through the machine.

Although labeled containers may seem less valuable than expensive knives or copper pans, protecting your dishwasher makes them one of the most practical 8 Things You Absolutely Should Not Put in a Dishwasher.

8. Insulated Mugs and Bottles That Are Not Labeled Dishwasher-Safe

Older kitchen advice often says never to place insulated drinkware in a dishwasher. Today, that statement needs an important qualification.

Some modern vacuum-insulated mugs and bottles are specifically designed for dishwasher use. Others require hand washing.

Therefore, the eighth entry among the 8 Things You Absolutely Should Not Put in a Dishwasher is not every insulated cup. It is insulated drinkware that the manufacturer does not identify as dishwasher-safe.

Current manufacturer instructions demonstrate why checking the product matters.

Stanley says many of its insulated stainless-steel products can go into the dishwasher, while also telling consumers to check the individual product and use the top rack when applicable. The company recommends hand washing products that lack dishwasher-safe approval.

Thermos similarly states that many of its current products are top-rack dishwasher-safe but still directs customers to each product’s care instructions.

That evidence provides an important reminder: blanket kitchen rules sometimes become outdated as manufacturers redesign products.

Before washing an insulated mug, turn it over and check the bottom. Then, look at the packaging or manufacturer’s care page if necessary.

If the manufacturer says hand wash only, use warm water, mild dish soap, and a bottle brush or soft sponge. Clean removable gaskets, straws, and lid components separately according to their instructions.

Also, allow all parts to dry completely before reassembly.

If the manufacturer approves dishwasher use, follow the recommended rack placement and cycle restrictions.

So, the final lesson from these 8 Things You Absolutely Should Not Put in a Dishwasher may be the most useful one: care labels outrank assumptions.

Frequently Asked Questions

Can sharp knives really become dull in a dishwasher?

Yes. Whirlpool warns that sharp knife blades can become nicked or dull and may strike dishwasher racks during washing. Hand washing helps protect the blade and also prevents exposed knives from becoming a hazard when someone unloads the dishwasher.

Can wooden spoons go in the dishwasher occasionally?

It is better to hand wash wooden spoons consistently. High heat, prolonged moisture, and repeated drying can cause wooden kitchenware to swell, warp, crack, or lose its finish.

What happens if I accidentally wash cast iron in the dishwasher?

A dishwasher may remove cast iron’s seasoning and encourage rust. If this happens, dry the pan thoroughly and follow the cookware manufacturer’s instructions for removing rust and restoring the seasoning.

Is all nonstick cookware unsafe for dishwashers?

No. Some manufacturers label specific nonstick products dishwasher-safe. However, other nonstick cookware should be hand washed, and dishwasher detergent and heat can damage certain coatings. Always follow the instructions supplied with your pan.

Are insulated tumblers safe in the dishwasher?

Some are, while others are not. For example, Stanley and Thermos currently sell insulated products that allow top-rack dishwasher cleaning, but both companies tell consumers to check individual product instructions. If your tumbler says hand wash only, keep it out of the dishwasher.

Conclusion

Knowing the 8 Things You Absolutely Should Not Put in a Dishwasher can save expensive cookware, preserve sentimental dishes, and protect the dishwasher itself.

Sharp knives deserve hand washing because dishwasher conditions can dull or nick their blades. Wooden utensils need gentler care because heat and moisture can make wood warp or crack. Likewise, cast iron should stay out because dishwasher cleaning can remove seasoning and promote rust.

Nonstick cookware requires manufacturer-specific care, while antique china and delicate crystal benefit from gentle hand washing. Copper, brass, and other specialty metals can discolor or lose their finish. Meanwhile, glued labels can come loose and create unwanted debris inside the appliance.

Finally, insulated drinkware proves why you should never rely only on old rules. Some modern insulated products are dishwasher-safe, while others are not. Therefore, always check the manufacturer’s label first.

The dishwasher remains one of the most useful appliances in the kitchen. However, convenience works best when you use the machine for items designed to handle its heat, detergent, moisture, and spray pressure.

Keep these 8 Things You Absolutely Should Not Put in a Dishwasher in mind whenever you load the racks. When an item seems delicate, valuable, unusually finished, or difficult to replace, check its care instructions before pressing Start.

A few minutes of hand washing today can help your favorite kitchen tools remain useful and beautiful for years.