🍽️ 8 Things You Should Never Put in the Dishwasher — and Why

Dishwashers are incredibly convenient, but not everything that looks washable is dishwasher-safe. High temperatures, powerful water jets, prolonged soaking, and strong detergents can damage certain materials.

Here are 8 common items that are better washed by hand.

1. 🔪 Good Kitchen Knives

Sharp chef’s knives and other quality blades are better kept out of the dishwasher.

The combination of hot water, detergent, and contact with racks or other utensils can:

• Dull the cutting edge
• Cause corrosion or discoloration
• Damage wooden or composite handles
• Create a safety hazard when loading and unloading

Better: Hand-wash sharp knives with mild dish soap and dry them immediately.

2. 🪵 Wooden Utensils and Cutting Boards

Wood can absorb water.

Repeated exposure to the dishwasher’s heat and prolonged moisture can cause wooden items to:

• Warp
• Crack
• Split
• Become rough
• Separate at glued joints

A wooden cutting board may also develop cracks where food and moisture can accumulate.

Better: Wash wooden utensils and boards by hand and dry them promptly. Periodically conditioning appropriate wooden boards with food-safe mineral oil can help maintain them.

3. 🥘 Cast-Iron Cookware

Traditional cast iron generally shouldn’t go into the dishwasher.

The combination of water and detergent can strip away the seasoning that protects the iron.

Repeated washing may leave the surface:

• Dull
• Sticky
• Rust-prone

Better: Clean cast iron according to the manufacturer’s recommendations, dry it thoroughly, and maintain its seasoning when appropriate.

What about enameled cast iron?

That’s different. Many enameled cast-iron manufacturers allow dishwasher use, although hand-washing can help preserve the finish. Always check the manufacturer’s instructions.

4. 🥫 Items Made of Copper

Copper cookware and decorative copper items can lose their appearance in the dishwasher.

Dishwasher detergents and heat may cause:

• Tarnishing
• Darkening
• Discoloration
• Damage to certain finishes

If you want copper to retain its characteristic appearance, hand-washing is generally safer.

5. 🥤 Insulated Travel Mugs and Some Thermoses

Be careful with vacuum-insulated containers.

Some are dishwasher-safe, while others aren’t.

Heat and water can potentially damage certain:

• Seals
• Vacuum-insulated layers
• Exterior finishes
• Decorative coatings

And even when the container itself is dishwasher-safe, the lid may have components that aren’t.

Better: Check the manufacturer’s label or instructions for the exact model.

6. 🧴 Some Plastics

“Plastic” doesn’t automatically mean dishwasher-safe.

Thin or low-quality plastics can warp or deform under high heat.

This is particularly important for containers that aren’t clearly labeled for dishwasher use.

Before washing plastic, look for the manufacturer’s dishwasher-safe marking or instructions.

A useful tip

If a plastic container is dishwasher-safe, placing it on the top rack can reduce exposure to the heating element in many machines.

But don’t assume this makes every plastic item safe.

7. 🥂 Delicate Crystal or Hand-Painted Glassware

Fine crystal, antique glassware, and hand-painted pieces can be damaged by the dishwasher’s heat, detergent, and water pressure.

Potential problems include:

• Clouding
• Etching
• Fading
• Cracking
• Damage to painted decorations

Some modern crystal and decorative glassware is specifically designed to be dishwasher-safe, so check the manufacturer’s instructions.

For valuable or sentimental pieces, hand-washing is the safer choice.

8. 🧂 Items With Non-Dishwasher-Safe Coatings

Some cookware and kitchen accessories have coatings that can deteriorate with repeated exposure to high temperatures and aggressive detergents.

This can include certain:

• Nonstick pans
• Decorative finishes
• Painted cookware
• Specialty baking equipment

A coating that is damaged may lose its intended performance and appearance.

Better: Check the manufacturer’s care instructions rather than assuming a nonstick or coated item belongs in the dishwasher.

⚠️ One Important Rule: “Dishwasher-Safe” Doesn’t Mean “Indestructible”

Manufacturers use different materials and coatings, so the exact item matters.

For example:

• Some plastics are dishwasher-safe; others melt or warp.
• Some insulated bottles are dishwasher-safe; others aren’t.
• Some nonstick pans can go in the dishwasher, but hand-washing may extend their lifespan.
• Some crystal is dishwasher-safe, while antique crystal isn’t.

When in doubt, look for the dishwasher-safe symbol or check the product’s care instructions.

🧼 Items That Often Surprise People

A few other things deserve caution:

• Aluminum: can discolor or become dull depending on the item and detergent.
• Wood-handled utensils: can crack or loosen.
• Items with glued parts: heat and water can weaken adhesives.
• Some graters and fine mesh strainers: food can remain trapped in difficult-to-clean areas.
• Decorative or antique dishes: their finishes may not tolerate modern dishwasher detergents.

🏆 The Simple Rule

Before putting something in the dishwasher, ask:

Is the material designed to tolerate heat, water, and strong detergent?

If you’re unsure, hand-washing with warm water and mild dish soap is usually the safer option.

And always remember: the manufacturer’s care instructions take priority over any general dishwasher rule.