A dishwasher is one of the most convenient appliances in the kitchen. Load the dirty dishes, add detergent, press a button, and let the machine handle the work.
But dishwasher-safe does not mean everything in your kitchen is dishwasher-safe.
High temperatures, powerful water jets, strong detergents, and heated drying can damage certain materials. Wood can warp, cast iron can rust, delicate decorations can fade, and some plastics can deform.
And although viral photos sometimes show dramatic dishwasher disasters, a picture alone usually can’t establish exactly what caused the damage. The best protection is knowing what belongs in the machine—and what should stay in the sink.
Here are 8 things you should think twice about before ever putting them in your dishwasher.
1. Wooden Cutting Boards, Spoons and Utensils
Wood is one of the easiest materials to damage in a dishwasher.
A dishwasher exposes an item to prolonged moisture, detergent and considerable heat. Untreated wooden items can consequently warp, crack or lose their finish.
That includes wooden cutting boards, salad bowls, wooden spoons and utensils with wooden handles.
What to do instead
Wash wooden kitchenware by hand with mild dish soap and warm water.
Don’t leave wooden boards soaking unnecessarily. After washing, dry them rather than leaving them wet for extended periods.
If you own an expensive wooden cutting board, follow its manufacturer’s maintenance recommendations, including any instructions about food-safe conditioning oil.
2. Cast-Iron Cookware
Your cast-iron skillet might survive decades of cooking.
That doesn’t mean it belongs in the dishwasher.
Cast iron relies on a seasoned surface that helps protect the metal and provides its characteristic cooking properties.
Dishwasher detergent and prolonged washing can strip that seasoning, exposing the iron underneath to moisture and potentially causing rust. Whirlpool explicitly lists cast iron as unsuitable for dishwashing for this reason.
What to do instead
Follow the cookware manufacturer’s cleaning instructions.
For traditional seasoned cast iron, hand washing followed by thorough drying is generally the better approach.
If the pan accidentally goes through the dishwasher and develops rust, it may still be recoverable through proper cleaning and reseasoning.
So don’t automatically throw it away.
3. Good Kitchen Knives
Putting a chef’s knife in the dishwasher may save a minute of hand washing.
It may also shorten the life of an expensive knife.
Whirlpool advises avoiding sharp kitchen knives because dishwasher washing can contribute to blades becoming nicked or dull, while knives may also damage dishwasher racks.
Some knives create another problem.
Hollow or multi-piece handles may use adhesives that can loosen during repeated exposure to dishwasher heat.
What to do instead
Wash quality kitchen knives by hand.
Clean the blade carefully with warm water and dish soap, rinse it and dry it promptly.
Don’t leave sharp knives hidden beneath soapy water where someone could accidentally grab the blade.
4. Delicate Crystal and Fine Glassware
That expensive crystal glass may look strong enough to survive a dishwasher.
But repeated dishwasher cycles can damage delicate glassware.
Heat, detergent, vibration and water pressure can contribute to etching, cloudiness, pitting or breakage in susceptible pieces.
Whirlpool notes that some crystal may be dishwasher-safe depending on the manufacturer, while certain types can etch with repeated washing.
So this isn’t a universal ban on every wine glass.
Modern sturdy glasses specifically marked dishwasher-safe may be perfectly suitable.
Antique, hand-blown, painted or particularly delicate pieces deserve much more caution.
What to do instead
Check the manufacturer’s instructions.
When you don’t know whether valuable crystal is dishwasher-safe, careful hand washing is generally the conservative choice.
5. Antique, Hand-Painted or Gold-Trimmed China
Grandmother’s china probably shouldn’t be treated like your everyday breakfast plate.
Dishwasher heat, water pressure and detergent can affect delicate decorative finishes.
Whirlpool specifically warns that antique, hand-painted and over-the-glaze patterns may fade, while gold-leaf decoration can discolor or fade.
The important distinction is that ordinary modern ceramic dishes may be dishwasher-safe.
Fine decorative china is another matter.
What to do instead
Hand wash valuable or sentimental pieces gently.
Don’t assume something is dishwasher-safe simply because it is ceramic.
If the manufacturer still exists, check its care recommendations.
For inherited or antique dishes where no instructions are available, err on the side of caution.
6. Copper, Brass, Pewter and Certain Reactive Metals
A beautiful copper pan can lose some of what makes it beautiful after repeated dishwasher exposure.
High temperatures and dishwasher detergents can cause certain metals to discolor, tarnish or pit.
Whirlpool recommends hand washing copper cookware and warns that pewter, brass and bronze can be discolored or pitted by dishwasher temperatures and detergent.
Cast iron isn’t the only metal that deserves special treatment.
Tin can also rust, while some aluminum finishes may change during dishwasher cleaning.
What to do instead
Hand wash specialty metal cookware according to the manufacturer’s instructions.
Dry it thoroughly afterward.
If maintaining a polished appearance matters, use a cleaner specifically recommended for that metal.
7. Disposable and Non-Dishwasher-Safe Plastics
This one can create an unpleasant surprise.
Not all plastic is the same.
Many sturdy reusable plastic containers are designed to tolerate dishwasher temperatures.
Thin disposable plastics often aren’t.
High temperatures can cause unsuitable plastic items to warp or deform. Whirlpool specifically lists disposable plastics as unable to withstand typical dishwasher temperatures and detergents.
Even dishwasher-safe plastic deserves proper placement.
Whirlpool recommends placing suitable plastic items on the top rack, and heated-dry cycles can be problematic for plastics with limited heat tolerance.
What to do instead
Look for a dishwasher-safe indication.
If the container is thin, disposable, damaged or not clearly intended for repeated high-temperature washing, wash it by hand or replace it when appropriate.
Never assume every takeout container belongs in the dishwasher.
8. Insulated Travel Mugs and Vacuum Containers Unless Specifically Marked Dishwasher-Safe
Your insulated coffee mug may look nearly indestructible.
The insulation system is the problem.
Some insulated containers use seals and construction methods that can be affected by dishwasher heat and water.
Whirlpool advises that insulated mugs and containers may be damaged because dishwasher water and heat can affect their seal and insulation.
However, modern products vary considerably.
Some manufacturers specifically design insulated bottles and tumblers to be dishwasher-safe.
What to do instead
Check the instructions for your exact bottle, mug or thermos.
If it says dishwasher-safe, follow the recommended rack placement.
If you can’t verify it, hand washing is the safer option.
Bonus: Never Put Regular Hand Dish Soap in the Dishwasher
This deserves special attention because it can create the kind of dramatic kitchen disaster people remember forever.
Dishwashing liquid for washing dishes by hand is not the same thing as automatic dishwasher detergent.
Regular hand dish soap is designed to produce lots of suds.
Inside a dishwasher, that can create excessive foam and potentially overflow from the appliance.
Whirlpool’s dishwasher manual specifically warns to use detergent intended for household dishwashers because other soaps can create excessive foaming and overflow, potentially causing poor washing performance and appliance problems.
So if you’ve run out of dishwasher tablets or automatic dishwasher detergent, don’t substitute ordinary liquid dish soap.
Wait until you have the correct product.
Another Surprising Item to Avoid: Bottles and Cans With Paper Labels
Putting an old jar or bottle into the dishwasher seems harmless.
But glued labels can detach during the cycle.
Loose paper and adhesive may then circulate inside the appliance and potentially interfere with the spray arms or pump. Whirlpool specifically recommends washing bottles and cans by hand for this reason.
If you’re reusing a glass jar, remove the label and adhesive first.
What About Nonstick Pans?
This one isn’t as simple as many viral articles suggest.
Some nonstick cookware manufacturers permit dishwasher cleaning.
Others recommend hand washing to extend the coating’s life.
Whirlpool’s general consumer guidance lists nonstick cookware among items best hand washed because dishwasher conditions may damage coatings.
But the instructions for your particular cookware should take priority.
If the manufacturer says dishwasher-safe, follow its directions.
If you’re uncertain, hand washing is the more conservative option.
What About Aluminum?
Again, it depends.
Some aluminum cookware can go into the dishwasher, while disposable aluminum and certain treated or anodized aluminum finishes can discolor or deteriorate.
Dishwasher heat and detergent can affect aluminum finishes, and manufacturer guidance varies by product.
Check the cookware label rather than relying on appearance alone.
What About Sterling Silver?
Silver is another category where blanket advice can be misleading.
Some silver or silver-plated items may be dishwasher-compatible under specific conditions, while valuable pieces are often better hand washed.
Whirlpool warns that prolonged contact with salty, acidic or sulfur-containing foods can affect silver. It also advises against allowing sterling or silver plate to directly contact stainless-steel flatware in the dishwasher because the contact can cause pitting.
For antique or valuable silver, follow specialist or manufacturer care instructions.
How Can You Tell Whether Something Is Dishwasher-Safe?
The easiest answer is:
Look for the manufacturer’s instructions.
Many modern kitchen products are labeled dishwasher-safe on the packaging, underside of the item or instruction manual.
If you’re unsure, don’t guess—particularly with something expensive or sentimental.
Dishwasher manufacturers themselves recommend checking the dishware or cookware manufacturer’s instructions when compatibility is uncertain.
Dishwasher-Safe Plastic Still Needs Proper Placement
Seeing “dishwasher-safe” on a plastic container doesn’t mean you can place it anywhere.
The lower portion of some dishwashers can expose items to greater heat, depending on the appliance design and drying system.
Whirlpool recommends placing dishwasher-safe plastic on the upper rack, and notes that heated drying may cause problems even for some heat-sensitive dishwasher-safe plastics.
Follow your particular dishwasher’s manual because modern appliance designs vary.
Don’t Block the Spray Arms
Putting an appropriate item in the dishwasher incorrectly can still cause problems.
Large cutting boards, trays, pans and utensils can interfere with the rotating spray arms.
Before starting a cycle, check that the arms can rotate freely.
Whirlpool notes that blocking spray arms can interfere with cleaning performance.
Oversized or heavy objects can also damage rack coatings when they’re forced into spaces where they don’t fit.
If an object doesn’t comfortably fit, wash it separately.
Don’t Overload the Dishwasher
Trying to squeeze one final plate between two already-packed dishes may seem efficient.
It can have the opposite effect.
Dishes need sufficient exposure to water and detergent.
Whirlpool advises against stacking items because doing so can obstruct water flow and prevent effective cleaning.
Give dishes enough separation for the machine to do its job.
What About the Broken Glass in the Viral Photo?
The image accompanying the viral post appears to show extensive broken material scattered around and inside a dishwasher.
However, the photograph alone does not tell us what happened.
We can’t reliably determine which object broke, whether it was dishwasher-safe, whether it had existing damage, or whether another incident caused the mess.
So it would be misleading to claim that putting one specific household item in the dishwasher will automatically produce the result shown in the photograph.
What we can say is that delicate or unsuitable glassware may break under dishwasher conditions, which is one reason manufacturers recommend checking whether glassware is dishwasher-safe before loading it.
What Should You Do If Glass Breaks Inside the Dishwasher?
First, don’t reach blindly into the appliance.
Broken glass can be difficult to see when mixed with water, detergent and food debris.
Turn the dishwasher off and allow everything to cool if the cycle was hot.
Wear suitable protective gloves and carefully remove large visible pieces.
Inspect the racks, bottom of the tub and filter area according to your dishwasher’s manual.
Small shards can be extremely difficult to spot.
If you believe glass has entered the pump or another inaccessible part of the machine, consult the manufacturer’s service instructions or a qualified appliance technician rather than dismantling components you’re unfamiliar with.
The Dishwasher Rule That Prevents Most Mistakes
Before putting an unfamiliar object into the dishwasher, ask:
Is it specifically labeled or documented as dishwasher-safe?
If yes, follow the manufacturer’s loading instructions.
If no—and the item is expensive, delicate, wooden, insulated, coated, antique or made from a reactive metal—hand washing may save you a much bigger headache.
Frequently Asked Questions
Can wooden spoons go in the dishwasher?
Generally, hand washing is preferable. Heat and prolonged moisture can cause untreated wood to warp, crack or lose its finish.
Can cast iron go in the dishwasher?
Traditional seasoned cast iron should not. Dishwasher washing can remove the seasoning and encourage rust.
Can chef’s knives go in the dishwasher?
It’s better to hand wash quality knives. Dishwasher conditions can dull or nick blades, and knives can damage the rack.
Can plastic containers go in the dishwasher?
Only when they’re dishwasher-safe. Thin disposable plastics may deform, while suitable reusable plastics are generally best placed on the upper rack according to the appliance and container instructions.
Can wine glasses go in the dishwasher?
Many sturdy modern wine glasses can, provided their manufacturer says they’re dishwasher-safe. Delicate, hand-painted, hand-blown or crystal glassware may require hand washing.
Can I use normal dish soap if I run out of dishwasher detergent?
No. Regular hand dishwashing liquid can create excessive suds and overflow. Use detergent specifically formulated for automatic dishwashers.
Can insulated travel mugs go in the dishwasher?
Some modern ones can, but others can suffer damage to seals or insulation. Check the manufacturer’s instructions for your exact product.
Is all china dishwasher-safe?
No. Ordinary modern china may be dishwasher-safe, but antique, hand-painted, over-glaze or gold-decorated pieces can fade or discolor.
Final Thoughts
Dishwashers are designed to handle tough cleaning, but they aren’t universal washing machines for everything in your kitchen.
The eight categories worth remembering are:
- Wooden utensils and cutting boards
- Cast-iron cookware
- Quality kitchen knives
- Delicate crystal and glassware
- Antique, hand-painted or gold-trimmed china
- Copper, brass, pewter and certain specialty metals
- Disposable or non-dishwasher-safe plastics
- Insulated mugs and vacuum containers unless approved by the manufacturer
And perhaps the most important dishwasher mistake of all has nothing to do with dishes:
Never replace automatic dishwasher detergent with ordinary hand dish soap.
When you’re unsure about an item, spending one minute checking the manufacturer’s care instructions is much easier than replacing a favorite pan, knife, cutting board—or cleaning up a kitchen full of suds and broken pieces.