Dishwashers save time, water, and effort, making them one of the most convenient appliances in the kitchen. But while they’re designed to handle plates, bowls, glasses, and cutlery, not everything belongs inside them.
The combination of high heat, powerful water jets, and strong detergents can permanently damage certain kitchen items. In some cases, putting the wrong item in the dishwasher can even damage the appliance itself.
If you want to keep your cookware, utensils, and dishwasher in excellent condition, here are eight things you should always wash by hand—and why.
Why Some Items Don’t Belong in the Dishwasher
A dishwasher cleans using hot water, detergent, and forceful spray arms. During a cycle, temperatures can exceed 60–70°C (140–160°F), and the detergent is often much harsher than standard washing-up liquid.
Some materials cannot tolerate this combination of heat, moisture, and chemicals, leading to:
- Warping
- Cracking
- Rust
- Dulling
- Discolouration
- Loss of protective coatings
- Reduced lifespan
Knowing which items require hand washing can save you money and help preserve your favourite kitchen tools.
1. Cast Iron Cookware
Cast iron skillets and Dutch ovens are prized for their durability, but they require special care.
Putting cast iron in the dishwasher can:
- Strip away the seasoned coating
- Cause rust to develop
- Reduce its natural non-stick surface
- Shorten its lifespan
Instead, clean cast iron with warm water, a soft brush, and dry it thoroughly before applying a light coating of cooking oil.
2. Sharp Kitchen Knives
Although many knives are labelled as dishwasher safe, experts generally recommend washing quality kitchen knives by hand.
Dishwasher cycles can:
- Dull sharp edges
- Damage wooden handles
- Cause corrosion over time
- Increase the risk of blades knocking against other utensils
Wash knives carefully with warm, soapy water and dry them immediately.
3. Wooden Utensils and Cutting Boards
Wood naturally absorbs water.
Repeated dishwasher cycles may cause wooden spoons, rolling pins, and chopping boards to:
- Crack
- Warp
- Split
- Fade
- Become rough
Hand washing with mild soap and drying immediately helps preserve the wood.
Occasionally conditioning wooden items with food-safe mineral oil can also prevent drying and cracking.
4. Non-Stick Cookware
Many newer non-stick pans are advertised as dishwasher safe, but repeated dishwasher use may gradually wear down the non-stick coating.
Harsh detergents and high temperatures can reduce the coating’s effectiveness over time.
To extend the life of non-stick cookware:
- Wash by hand with a soft sponge.
- Avoid abrasive scrubbers.
- Never use metal utensils on the cooking surface.
5. Fine China and Delicate Glassware
Decorative dishes, crystal glasses, and heirloom china deserve extra care.
Dishwasher cleaning may lead to:
- Chipping
- Cloudiness
- Fading decorative patterns
- Fine scratches
Delicate items are safest when washed gently by hand.
6. Insulated Travel Mugs and Vacuum Bottles
Many insulated mugs rely on a vacuum seal between two layers of stainless steel.
Dishwasher heat may damage these seals, reducing the mug’s ability to keep drinks hot or cold.
Always check the manufacturer’s instructions before placing insulated drinkware in the dishwasher.
7. Aluminium Cookware
Bare aluminium reacts with dishwasher detergents.
Repeated washing can cause:
- Dark staining
- Discolouration
- Pitting
- Dull finishes
Anodised aluminium is often more durable, but it’s still wise to follow the manufacturer’s cleaning recommendations.
8. Copper Cookware
Copper pots and pans develop a beautiful shine when properly maintained.
Dishwasher detergent can quickly dull the finish and may encourage tarnishing.
Hand washing with mild detergent and occasional polishing helps maintain copper’s appearance.
Other Items to Wash by Hand
In addition to the eight items above, many experts recommend hand washing:
- Cheese graters with wooden handles
- Decorative serving platters
- Antique kitchenware
- Measuring cups with printed markings
- Plastic items labelled “hand wash only”
- Pressure cooker lids with rubber seals
- Fine serving utensils
- Certain food storage containers that may warp under high heat
Always check the manufacturer’s care instructions if you’re unsure.
Tips for Using Your Dishwasher Safely
To keep your dishwasher performing well:
- Scrape large food scraps into the bin before loading.
- Don’t overload the racks.
- Place fragile items securely.
- Use dishwasher-safe detergent only.
- Clean the filter regularly.
- Leave enough space between dishes for water to circulate.
- Run a cleaning cycle periodically to reduce grease and limescale buildup.
A well-maintained dishwasher cleans more efficiently and lasts longer.
Common Dishwasher Myths
Myth: If it fits, it’s dishwasher safe.
Fact: Many items fit inside the dishwasher but may still be damaged by heat, detergent, or water pressure.
Myth: Dishwasher-safe means dishwasher-proof.
Fact: Even dishwasher-safe items may wear out more quickly with frequent machine washing.
Myth: Hotter water always cleans better.
Fact: Higher temperatures may damage delicate materials while offering little additional benefit for certain items.
Myth: Dishwashers sterilise everything.
Fact: While dishwashers clean effectively, not every cycle reaches temperatures required for true sterilisation.
Frequently Asked Questions
Can I wash stainless steel in the dishwasher?
Most stainless steel cookware and cutlery are dishwasher safe, but avoid placing stainless steel in direct contact with silver during the wash cycle, as this can sometimes cause a chemical reaction that discolours the metals.
Why do glasses become cloudy?
Cloudiness may result from hard water mineral deposits or permanent etching caused by repeated exposure to harsh detergents and high heat.
Is plastic safe in the dishwasher?
Only plastics labelled as dishwasher safe should be placed in the dishwasher. Position lightweight plastic items on the top rack, where temperatures are generally lower.
Can I put wooden-handled knives in the dishwasher?
No. The heat and moisture can damage the wood, loosen the handle, and shorten the knife’s lifespan.
Final Thoughts
Your dishwasher is one of the hardest-working appliances in the kitchen, but it’s not designed to clean everything. Items made from wood, cast iron, copper, delicate glass, and certain specialty materials can suffer permanent damage from repeated exposure to high temperatures, strong detergents, and powerful water jets.
Taking a few extra minutes to hand wash these items can help preserve their appearance, performance, and longevity. By understanding what belongs in the dishwasher—and what doesn’t—you’ll protect your kitchen investments and keep both your cookware and your dishwasher in excellent condition for years to come.