8 Things You Should Never Put in the Dishwasher (And Why)

Dishwashers are one of the greatest time-saving appliances in the modern kitchen. They make cleanup faster, save water compared to hand washing in many cases, and leave dishes sparkling clean.

However, not everything belongs inside a dishwasher.

High temperatures, strong water pressure, and harsh detergents can permanently damage certain materials, shortening their lifespan or even making them unsafe to use.

Here are eight common household items that are better washed by hand.

1. Sharp Kitchen Knives

Although many dishwasher-safe knife sets exist, hand washing is generally the better option.

The combination of heat, detergent, and movement during the wash cycle can:

• Dull sharp edges
• Damage handles
• Increase the risk of blades knocking against other utensils

A quick wash with warm water and mild soap helps preserve both sharpness and appearance.

2. Cast Iron Cookware

Cast iron pans are famous for their natural seasoning—a protective layer built over time through cooking.

Dishwasher detergents can strip away this seasoning, leaving the surface vulnerable to rust.

Instead:

• Wash with warm water.
• Use a soft brush if necessary.
• Dry immediately.
• Apply a thin coat of cooking oil afterward.

3. Wooden Utensils and Cutting Boards

Wood naturally expands and contracts when exposed to moisture and heat.

Repeated dishwasher cycles may cause:

• Cracking
• Warping
• Splitting
• Fading

Hand washing and immediate drying help wooden kitchen tools last for many years.

4. Nonstick Pans

Some newer nonstick cookware is labeled dishwasher-safe, but repeated machine washing may gradually reduce the life of the nonstick coating.

Hand washing with a soft sponge is gentler and often extends the cookware’s performance.

5. Crystal Glassware

Fine crystal can lose its brilliance after repeated dishwasher cycles.

High temperatures and powerful detergents may cause:

• Cloudiness
• Scratches
• Small chips

Delicate glassware is usually safest when washed carefully by hand.

6. Copper Items

Copper pots, pans, and decorative serving pieces can tarnish quickly in a dishwasher.

Harsh detergents may dull their beautiful finish.

To maintain their shine, wash them gently with warm water and dry them immediately.

7. Insulated Travel Mugs

Many insulated bottles and travel mugs rely on a vacuum seal between their inner and outer walls.

High dishwasher temperatures may damage that seal, reducing the mug’s ability to keep beverages hot or cold.

Unless the manufacturer specifically states otherwise, hand washing is usually recommended.

8. Aluminum Cookware

Certain aluminum items may become discolored or develop a dull finish after repeated dishwasher use.

Some detergents can even react with aluminum, causing dark spots or staining.

Gentle hand washing helps preserve the metal’s appearance.

How to Tell if Something Is Dishwasher-Safe

Before placing unfamiliar cookware or utensils into the dishwasher:

• Check the manufacturer’s instructions.
• Look for a dishwasher-safe symbol on the bottom.
• When uncertain, hand washing is often the safer choice.

A few extra minutes of care can significantly extend the life of your kitchen equipment.

Final Thoughts

While dishwashers are incredibly convenient, they’re not suitable for every kitchen item.

Protecting knives, cast iron, wood, crystal, copper, insulated drinkware, aluminum cookware, and many nonstick surfaces through hand washing can help preserve their quality for years to come.

Knowing what stays out of the dishwasher is just as important as knowing what goes in—and your favorite kitchen tools will thank you for it.