8 Things You Absolutely Shouldn’t Wash in the Dishwasher (and Why)
Think everything belongs in the dishwasher? Think again. Discover 8 common kitchen items that can warp, rust, crack, or lose their finish.
The dishwasher is one of those appliances that feels almost too convenient to question.
Scrape the plate. Open the door. Toss everything inside. Press a button. Walk away.
But there’s a catch: not everything that fits inside a dishwasher belongs there.
The combination of hot water, powerful detergent, high-pressure spray, humidity, and heated drying can quietly damage certain kitchen essentials. Sometimes the damage is obvious—a warped cutting board or rusty cast-iron pan. Other times, it happens gradually, such as a dull knife blade, a fading decorative finish, or a weakened nonstick coating.
And there’s an especially frustrating part: an item can survive the dishwasher ten times before suddenly looking terrible on the eleventh.
So before you load tonight’s dishes, take a quick look at these eight categories. A few seconds of hand washing could save you from replacing expensive cookware, favorite knives, or sentimental dishes.
1. Wooden Cutting Boards and Wooden Utensils
Wood and dishwashers are a bad combination for a simple reason: wood absorbs water, and dishwashers expose it to prolonged heat and moisture.
That combination can cause wooden cutting boards, spoons, spatulas, salad bowls, and utensils to swell, warp, crack, or lose their finish. Whirlpool specifically recommends hand washing wooden cutting boards and wooden-handled knives.
A cutting board may look perfectly normal when it comes out of the dishwasher.
The problem often becomes obvious later.
Repeated cycles can cause tiny cracks and changes in the shape of the board. Once a wooden board starts to split or warp, it becomes less pleasant to use and much harder to keep in good condition.
What to do instead
Wash wooden items by hand with warm water and mild dish soap. Avoid soaking them unnecessarily, then dry them promptly rather than leaving them sitting wet in the sink.
For wooden cutting boards, occasional conditioning with a food-safe board oil or conditioner can also help maintain the wood, following the board manufacturer’s instructions.
What about bamboo?
Bamboo is still a plant-based material and can suffer from repeated exposure to dishwasher heat and moisture. Some manufacturers specifically label bamboo products as dishwasher-safe, while others don’t.
The manufacturer’s instructions win.
If there is no dishwasher-safe marking or care guidance, hand washing is the safer choice.
2. Cast-Iron Cookware
If there is one piece of cookware you should think twice about putting in the dishwasher, it is cast iron.
The problem isn’t merely that the pan gets wet.
Cast iron relies on a seasoned surface—a layer developed through cooking and applying oil—to help protect the metal and provide its characteristic cooking surface.
A dishwasher’s hot water and detergent can strip away that seasoning. Once the protective layer is damaged, the exposed iron becomes much more vulnerable to rust.
And that beautifully seasoned skillet you’ve spent years developing?
A dishwasher can undo a lot of that work surprisingly quickly.
What about enameled cast iron?
This is where things get less absolute.
Some enameled cast-iron cookware may be labeled dishwasher-safe. However, manufacturers may still recommend hand washing to preserve the finish.
Always check the care instructions for the specific piece.
The better method
For a traditional seasoned cast-iron skillet:
- Let it cool enough to handle safely.
- Remove food residue.
- Wash with a small amount of dish soap and water if needed.
- Dry it thoroughly.
- Apply a thin layer of cooking oil if appropriate for your pan’s care routine.
The goal is simple: keep water exposure brief and protect the seasoning.
3. Sharp Kitchen Knives
Putting your kitchen knives in the dishwasher may seem harmless.
After all, they’re made of metal, right?
The problem is that a dishwasher isn’t designed to gently care for a precision cutting edge.
During a cycle, knives can knock against other utensils or the dishwasher racks. High heat, detergent, and prolonged moisture can also affect certain handles, adhesives, and finishes.
Whirlpool and Maytag both recommend avoiding dishwasher washing for kitchen knives, particularly sharp or specialized knives.
There’s another problem that’s easy to overlook: the knife can damage the dishwasher.
Sharp objects can scratch or gouge the protective coating on dishwasher racks. Damaged rack coatings can expose the underlying metal, which may eventually rust.
The 20-second solution
Hand washing a knife doesn’t have to become a chore.
Use warm water, a little dish soap, and a soft sponge. Wash the blade carefully, keeping the sharp edge pointed away from your hand.
Then dry it immediately.
That takes less time than searching for a new chef’s knife because the old one has become dull.
One more warning: never leave sharp knives hidden in soapy water
This is not just about protecting the knife.
A knife sitting underneath cloudy dishwater creates an unnecessary hand injury risk. Wash it individually and put it away.
4. Nonstick Pans
Nonstick cookware is another category where the dishwasher can be harder on the item than you realize.
Depending on the specific coating and manufacturer’s instructions, dishwasher cleaning may contribute to wear of the nonstick surface. Maytag recommends hand washing to help protect nonstick coatings, while manufacturer instructions should always take priority because dishwasher compatibility varies by product.
The important word here is manufacturer.
Some modern nonstick cookware is explicitly labeled dishwasher-safe.
That does not necessarily mean the dishwasher is the best choice if your goal is maximum longevity.
Why hand washing makes sense
A nonstick pan generally doesn’t require aggressive scrubbing.
Use warm water, mild dish soap, and a soft sponge.
Avoid abrasive scrubbers that can scratch the coating.
And never use metal utensils unless the manufacturer specifically says they’re appropriate for that cookware.
The surprising mistake
Many people focus entirely on whether the pan is “dishwasher-safe.”
But cookware can be dishwasher-safe and still experience more wear from repeated dishwasher cycles than from gentle hand washing.
If you paid a premium for a nonstick pan, protecting the coating may be worth those extra 30 seconds at the sink.
5. Insulated Travel Mugs and Containers
This one catches people off guard.
Your travel mug may look like a normal cup, but an insulated bottle or mug can contain multiple components designed to work together to maintain temperature.
Heat and repeated dishwasher exposure can potentially affect seals, insulation components, lids, adhesives, or decorative finishes. Whirlpool specifically advises caution with insulated mugs and containers and notes that water and heat can damage seals and insulation.
Don’t assume the stainless steel body tells the whole story
A stainless-steel travel mug might appear indestructible.
But the stainless-steel exterior is only one part of the product.
The lid may contain:
- Silicone seals
- Plastic components
- Valves
- Gaskets
- Adhesives
- Moving mechanisms
One component may be dishwasher-safe while another isn’t.
Best approach
Check the manufacturer’s instructions.
If the entire product isn’t dishwasher-safe, wash it by hand.
And pay particular attention to removable silicone gaskets and seals. Those components can trap moisture and residue if they’re never removed for cleaning.
6. Fine China, Hand-Painted Dishes, and Decorative Dinnerware
Your everyday white plates are one thing.
Your grandmother’s hand-painted china is another.
Decorative dishes can contain finishes, metallic details, decals, or hand-painted designs that aren’t designed to withstand repeated dishwasher cycles.
High water pressure, detergent, heat, and repeated washing can cause designs to fade or finishes to deteriorate. Whirlpool and Maytag specifically caution against dishwashing antique, hand-painted, and metal-rimmed china.
The biggest offenders
Be especially careful with:
- Gold rims
- Silver rims
- Hand-painted patterns
- Antique china
- Delicate decorative finishes
- Heirloom dishes
- Older ceramics with uncertain care instructions
The dishwasher may not destroy them immediately.
That’s what makes this mistake so easy to repeat.
The damage can be gradual.
A gold rim becomes slightly dull.
A painted pattern becomes less vibrant.
Eventually, you realize that the dish you loved doesn’t look quite the way it used to.
What to do instead
Hand wash delicate or sentimental pieces with a mild detergent and soft sponge.
And don’t stack delicate china directly against other pieces in the sink.
Treat it like something you intend to keep for decades—not something you’re trying to get through Tuesday night’s cleanup.
7. Crystal and Delicate Glassware
Not every glass belongs in the dishwasher.
Sturdy everyday drinking glasses generally handle dishwasher cleaning well when the manufacturer says they’re dishwasher-safe. But delicate crystal and specialty glassware can be much more vulnerable.
Repeated dishwasher cycles may contribute to scratching, breakage, or clouding, depending on the type of glass and the conditions of the wash cycle. Maytag notes that some delicate or leaded crystal can etch with repeated dishwasher washing.
And then there’s the physical problem.
A thin wine glass doesn’t have much tolerance for being bumped around.
One bad placement can be enough.
If you value the glass, wash it by hand
Use warm—not extremely hot—water.
Use a soft sponge or cloth.
Avoid gripping a delicate glass by the stem while twisting the bowl aggressively. That can place unnecessary stress on the narrow connection between the two.
Rinse carefully and allow the glass to dry.
For everyday sturdy glassware labeled dishwasher-safe, the dishwasher is generally fine.
The key is knowing the difference between ordinary glass and delicate glassware.
8. Copper, Brass, Pewter, and Certain Specialty Metals
Metal doesn’t automatically mean dishwasher-safe.
Copper is a classic example.
A shiny copper pan or serving piece can lose its finish, become dull, or develop discoloration after dishwasher exposure. Maytag recommends hand washing copper cookware to preserve its appearance.
Pewter, brass, and bronze can also react poorly to high temperatures and dishwasher detergents, potentially causing discoloration or surface damage.
What about aluminum?
This category needs nuance.
Some aluminum cookware is dishwasher-safe, while anodized aluminum or certain finishes can be affected by high temperatures and detergents.
That is why the safest rule isn’t:
“Never put aluminum in the dishwasher.”
Instead:
Check the manufacturer’s care instructions for that exact item.
When the finish matters, hand washing is usually the more conservative option.
The dishwasher-safe label isn’t meaningless—but it isn’t universal
One of the biggest misconceptions about dishwashers is that there is one universal definition of “dishwasher-safe.”
There isn’t.
Different manufacturers test and rate products according to their own specifications. Whirlpool notes that the term generally refers to an item’s ability to withstand the heat, water pressure, and detergent involved in a dishwasher cycle without unacceptable damage.
That means two objects made from seemingly identical materials can have different care instructions.
For example:
- One plastic container may be dishwasher-safe.
- Another may warp.
- One insulated mug may be dishwasher-safe.
- Another may not be.
- One nonstick pan may tolerate a dishwasher.
- Another manufacturer may recommend hand washing.
So when you’re uncertain, don’t rely solely on appearance.
Look for the dishwasher-safe symbol or check the manufacturer’s care instructions.
A quick comparison: dishwasher or hand wash?
| Item | Best choice | Main concern |
|---|---|---|
| Wooden cutting board | Hand wash | Warping, cracking, swelling |
| Wooden utensils | Hand wash | Heat and moisture damage |
| Cast iron | Hand wash | Seasoning loss and rust |
| Sharp knives | Hand wash | Dulling, damage, rack scratches |
| Nonstick cookware | Usually hand wash | Coating wear |
| Insulated travel mug | Check manufacturer; often hand wash | Seals and insulation |
| Hand-painted china | Hand wash | Fading and finish damage |
| Delicate crystal | Hand wash | Etching, breakage |
| Copper cookware | Hand wash | Discoloration and finish damage |
| Everyday dishwasher-safe glass | Dishwasher | Generally low risk |
The word “usually” matters.
Product construction varies, so the care label for your particular item should always take priority.
What you can usually put in the dishwasher
Fortunately, this doesn’t mean you have to hand wash your entire kitchen.
Many ordinary household items are designed for dishwasher cleaning.
Common examples include:
- Standard ceramic plates
- Everyday bowls
- Dishwasher-safe drinking glasses
- Stainless-steel flatware
- Dishwasher-safe hard plastics
- Silicone utensils labeled dishwasher-safe
- Many glass baking dishes
- Many stoneware pieces
Whirlpool lists everyday china and ceramic dishware, hard plastic, stainless steel, sturdy glassware, glass and stoneware baking dishes, and silicone and metal utensils among common dishwasher-safe categories, subject to manufacturer instructions.
So the goal isn’t to fear the dishwasher.
It’s to use it selectively.
What about plastic containers?
Plastic deserves its own quick warning because “plastic” isn’t one material.
Some hard plastics are dishwasher-safe.
Others can warp or melt, particularly when exposed to high heat or heated-dry cycles. Whirlpool recommends checking the dishwasher-safe marking and notes that heated drying can be particularly hard on heat-sensitive plastics.
A simple rule
If a plastic container doesn’t clearly say dishwasher-safe, don’t assume it is.
And when the manufacturer recommends the top rack, follow that instruction.
The top rack generally places plastic farther from the dishwasher’s heating element, reducing exposure to intense heat.
The heated-dry setting deserves more attention
Here’s something many people forget:
The dishwasher isn’t finished when the washing stops.
A heated-dry cycle can expose items to additional heat after the cleaning phase.
That can be perfectly useful for materials designed to tolerate it.
But for certain plastics, insulated mugs, wood, adhesives, and delicate finishes, extra heat can make an already risky dishwasher cycle worse.
If you’re washing an item that is dishwasher-safe but heat-sensitive, follow the manufacturer’s instructions about rack placement and drying settings.
And if an item isn’t dishwasher-safe in the first place, switching off heated dry doesn’t necessarily make it safe.
Three dishwasher mistakes that damage perfectly good items
The problem isn’t always the dishwasher itself.
Sometimes it’s how the dishwasher is loaded.
Blocking the spray arms
Large cutting boards, pans, or improperly positioned dishes can interfere with the spray arms.
That prevents water from reaching everything properly and can reduce cleaning performance.
Before starting a cycle, spin the spray arm by hand.
If it hits something, rearrange the load.
Overcrowding
A packed dishwasher may look efficient.
But if plates and bowls are touching or blocking one another, detergent and water can’t reach all surfaces properly.
Give dishes enough space for water to circulate.
Ignoring manufacturer instructions
This is probably the biggest one.
The internet can tell you that stainless steel is dishwasher-safe.
It cannot tell you whether the specific stainless-steel travel mug sitting on your counter has a dishwasher-safe gasket.
The manufacturer’s instructions are the final word.
What to do when you’re unsure
Use this five-second decision process:
1. Check the bottom or packaging.
Look for a dishwasher-safe symbol or care instructions.
2. Identify the material.
Is it wood? Cast iron? Crystal? Copper? Plastic? Nonstick?
Material is a major clue.
3. Look for coatings or decorations.
Metallic rims, painted designs, nonstick surfaces, adhesives, and seals can change the answer.
4. Consider whether the item is valuable or sentimental.
If replacing it would genuinely upset you, hand washing is the safer bet.
5. When in doubt, wash by hand.
A few extra seconds at the sink are cheaper than replacing a favorite pan or heirloom dish.
The 30-second kitchen habit that prevents most dishwasher disasters
Before you start the dishwasher, scan the load.
Look for:
- Wooden handles
- Cutting boards
- Sharp knives
- Cast iron
- Nonstick cookware
- Copper
- Delicate glass
- Hand-painted dishes
- Insulated travel mugs
- Unmarked plastic
- Anything expensive or sentimental
Pull those items out.
Then check that nothing is blocking the spray arms.
Finally, make sure plastic items that are dishwasher-safe are positioned according to the manufacturer’s instructions.
That’s it.
You don’t need a complicated dishwasher system.
You need a quick final inspection.
A simple rule worth remembering
If an item is made to be tough, heat-resistant, and repeatedly washed, the dishwasher is probably its friend.
If it is made from wood, delicate glass, seasoning-dependent iron, decorative finishes, precision blades, insulation, or vulnerable coatings, pause before loading it.
That one mental shortcut will prevent a surprising number of kitchen mishaps.
Final Thoughts
Dishwashers are remarkably good at what they’re designed to do—but they’re not universal cleaning machines.
The dishwasher saves time—but using it on the wrong items can turn convenience into an expensive mistake. Knowing what to keep out is just as important as knowing what to put in.