8 Things You Should Never Put in the Dishwasher (And Why)
A dishwasher can save you a huge amount of time, but “dishwasher-safe” doesn’t mean everything in your kitchen is safe to wash in it.
Hot water, powerful jets, strong detergents, prolonged heat, and the drying cycle can damage certain materials. In some cases, the item may survive a few washes but gradually become discolored, warped, dull, cracked, or unsafe to use.
Here are eight things that are generally better washed by hand.
1. Wooden Cutting Boards and Utensils
Wood is naturally porous and responds to heat and moisture.
Repeated dishwasher cycles can cause wooden items to:
- Warp
- Crack
- Split
- Lose their finish
- Develop rough surfaces
The combination of hot water and prolonged drying is particularly hard on wood.
Better approach
Wash wooden cutting boards, spoons, spatulas, and similar items by hand with warm water and mild dish soap. Dry them promptly rather than leaving them submerged.
Occasionally conditioning a wooden cutting board with an appropriate food-safe board oil can help maintain its surface, following the manufacturer’s recommendations.
2. Cast-Iron Cookware
Traditional cast iron generally shouldn’t go through a dishwasher.
Dishwasher detergent and prolonged exposure to water can strip away the seasoning that protects the surface.
The result can be:
- Dull or rough cookware
- Loss of nonstick performance
- Rust
Better approach
Clean cast iron according to the manufacturer’s instructions. In many cases, that means washing it relatively quickly, drying it thoroughly, and maintaining its seasoning.
One important exception: some enameled cast-iron cookware is dishwasher-safe, although frequent dishwasher use can still affect its appearance over time. Check the manufacturer’s instructions.
3. Nonstick Pans
Many nonstick pans can technically tolerate a dishwasher, but that doesn’t necessarily mean frequent dishwasher washing is ideal.
High heat, strong detergent, and repeated cycles can gradually degrade some nonstick coatings and affect the pan’s appearance.
Better approach
Unless the manufacturer specifically recommends dishwasher cleaning, hand-wash nonstick cookware with a soft sponge and mild detergent.
Avoid abrasive scrubbers that can damage the coating.
4. Sharp Knives
Putting good kitchen knives in the dishwasher can be a poor choice.
The powerful spray, heat, detergent, and contact with other objects can dull or damage the blade.
Knives can also move around during a cycle and potentially damage other dishes or the dishwasher itself.
Dishwasher detergent can also be harsh on some knife handles and finishes.
Better approach
Wash quality knives by hand using warm water and mild soap.
Dry them immediately.
And be careful when placing a sharp knife in the sink—don’t bury it beneath soapy water where someone could accidentally grab the blade.
5. Crystal and Delicate Glassware
Fine crystal and delicate glassware can be vulnerable to high temperatures, strong detergents, and mechanical impact.
Repeated dishwasher cycles may lead to:
- Cloudiness
- Etching
- Scratches
- Cracks
- Breakage
Some modern crystal products are specifically designed to be dishwasher-safe, so check the manufacturer’s instructions.
Better approach
For valuable or delicate glassware, hand-washing is usually the safer choice.
Use lukewarm water, mild detergent, and a soft cloth or sponge.
6. Copper and Some Other Reactive Metals
Copper cookware and decorative copper items can lose their appearance in a dishwasher.
Dishwasher detergents and heat can cause:
- Tarnishing
- Discoloration
- Loss of shine
Some copper cookware is lined with another metal, but that doesn’t automatically make it dishwasher-safe.
Better approach
Follow the manufacturer’s cleaning instructions.
If maintaining the copper’s appearance is important, hand-washing is generally preferable.
7. Insulated Travel Mugs and Vacuum Flasks
This one requires checking the specific product.
Some insulated bottles and travel mugs are dishwasher-safe, while others aren’t.
High heat and aggressive detergent can potentially damage:
- Exterior finishes
- Printed designs
- Seals
- Gaskets
- Vacuum-insulated components
Certain lids have multiple small pieces that can also trap water or detergent.
Better approach
Look for the dishwasher-safe symbol or check the manufacturer’s instructions.
If the manufacturer recommends hand-washing, follow that recommendation.
8. Items With Delicate Labels, Decorations, or Glued Components
Anything decorated with delicate paint, printed designs, metallic trim, stickers, or glued components deserves caution.
The dishwasher can gradually remove or fade decorative details.
This can include:
- Hand-painted mugs
- Vintage dishes
- Decorative ceramics
- Items with gold or silver trim
- Some personalized cups
- Certain antiques
Better approach
Hand-wash items that are sentimental, valuable, antique, or visibly delicate.
When in doubt, preserving the item is usually more important than saving a few minutes of washing.
A Bonus: Items You Should Check Before Washing
There are several categories that aren’t universally forbidden but depend heavily on the manufacturer.
These include:
- Aluminum cookware
- Silicone baking products
- Plastic containers
- Nonstick cookware
- Insulated bottles
- Food processors and blender components
- Ceramic knives
- Certain pressure-cooker parts
Look for the dishwasher-safe symbol or consult the manufacturer’s instructions.
Be Careful With Plastic
Plastic deserves special attention.
Some plastics are dishwasher-safe, while others can warp or deteriorate under high heat.
If an item is labeled dishwasher-safe, place it where the manufacturer recommends. Some plastics should go on the top rack, farther from the heating element.
Never assume that every plastic container is suitable simply because it doesn’t melt immediately.
What About Wooden Cutting Boards?
If you regularly use a wooden cutting board, don’t worry that hand-washing means it isn’t hygienic.
Clean it promptly after use with hot water and dish soap, then allow it to dry thoroughly.
For raw meat and poultry, use appropriate food-safety practices and consider having separate cutting boards for different food categories.
The bigger concern isn’t whether the board goes into the dishwasher—it’s whether it is properly cleaned, dried, and maintained.
What Happens When You Ignore These Rules?
The consequences aren’t always dramatic.
Often, dishwasher damage is cumulative.
An item may look perfectly fine after its first wash.
After dozens of cycles, you may notice:
fading → cloudiness → cracking → warping → deterioration.
That’s why manufacturer instructions matter more than a blanket internet rule.
How to Know Whether Something Is Dishwasher-Safe
Before putting an unfamiliar item in the machine:
- Check the bottom or handle for a dishwasher-safe symbol.
- Look at the packaging or manufacturer’s website.
- Check whether the item contains wood, natural stone, delicate coatings, or glued components.
- When uncertain, hand-wash it.
Also remember that “dishwasher-safe” can mean different things depending on the manufacturer’s testing. Some products may be safe only on the top rack or on a particular cycle.
The Bottom Line
The eight categories most worth keeping out of the dishwasher are:
- Wooden cutting boards and utensils — heat and moisture can cause warping and cracking.
- Traditional cast iron — detergent and water can remove seasoning and encourage rust.
- Many nonstick pans — repeated harsh cycles can shorten the coating’s useful life.
- Quality kitchen knives — dishwasher cycles can dull blades and damage handles.
- Delicate crystal — heat and detergent can cause cloudiness, etching, or breakage.
- Copper items — dishwasher detergents can cause tarnishing and discoloration.
- Some insulated bottles and travel mugs — heat can affect finishes, seals, and components.
- Decorated or antique items — paint, metallic trim, and delicate finishes can deteriorate.
When in doubt, check the manufacturer’s instructions. A few minutes of hand-washing is often worth it when the alternative is damaging an expensive pan, favorite knife, heirloom glass, or sentimental dish.
