Your dishwasher blasts everything with hot water, strong detergent and a lot of banging around. Most dishes shrug it off. But some kitchen essentials can lose their finish, develop rust, warp or simply wear out faster in the machine, and a few of the things you should never put in the dishwasher look tough enough to survive it.

Here are six to know about. Three are best kept out of the dishwasher. Three depend on the material or the label, so it pays to check before you load.

Three things to keep out of the dishwasher

1. Cast iron

Lodge, the best-known name in cast iron, is direct about it: a dishwasher will remove the seasoning and likely cause rust. Seasoning is the baked-on layer of oil that protects the iron and gives the pan its slick surface, and losing it leaves the iron more vulnerable to rust.

Do this instead: wash it by hand and dry it completely right away. Lodge says a little dish soap is fine, but soaking is a recipe for rust.

2. Kitchen knives

Wüsthof tells owners not to put its knives in the dishwasher because of the high temperatures and the rubbing that happens during the wash cycle. Neither is kind to a fine edge or a handle, and a rack full of other dishes gives a blade plenty to bang into.

Do this instead: hand wash right after use with warm water and mild soap, then dry immediately with a soft cloth.

3. Copper cookware

Mauviel, the French copper maker, says it’s not advised to use a dishwasher because the harsh chemicals in some dishwasher detergents can shorten the life of the cookware, and its guide warns that bleach-based cleaners are corrosive and will cause copper to pit. Other makers’ rules can differ, so check yours, but for most copper the finish is the thing at risk.

Do this instead: use a soft sponge or cloth, warm water and a copper polish or paste, then rinse and dry. A little darkening with age is normal, and Mauviel says a quality polish helps maintain the warm glow.

Three things to check before you load them

These aren’t blanket bans. Whether they can go in depends on the construction, the model or the label, so read it.

4. Wooden cutting boards

This one surprises people. The University of Wisconsin Extension says solid wood boards can be washed in a dishwasher, while laminated boards may crack and split. Board makers are more cautious, though, and one warns that prolonged exposure to heat and water will cause a board to warp and crack. The same extension page says to replace any board with cracks or grooves where bacteria can hide.

Do this instead: if you’re not sure how your board is made, wash it with hot, soapy water, rinse, and dry it standing on its edge. Regular oiling helps wood cope with moisture swings.

5. Nonstick pans

Nonstick cookware is another case where dishwasher safe doesn’t necessarily mean best for the pan. T-fal recommends hand washing only to extend the life of its pans, and says that if you do use a dishwasher, corrosive detergents can dull and discolor the pan, so tablets and sachets are best avoided. Other manufacturers allow the dishwasher on certain nonstick lines but still suggest hand washing to protect the coating. Check the care instructions for your exact pan before loading it.

Do this instead: let the pan cool, then wash with warm, sudsy water and a nylon sponge or soft brush. T-fal warns against scouring powders and pads.

6. Insulated tumblers and mugs

Don’t assume an insulated cup has to be hand washed, or that it can go in the dishwasher. YETI says all its Rambler drinkware is dishwasher safe, but other brands restrict certain models, lids or finishes. Guidance varies by manufacturer, model and material.

Check your exact model. If you can’t find its care page, hand wash the cup and pull the lid, straw and gasket off to wash separately. When you do use the dishwasher, YETI suggests putting lids on the top rack away from the heat.

The pattern behind all six

The pattern is pretty simple: heat, detergent, moisture and friction can be hard on certain materials and finishes. When you’re unsure, the care instructions for the specific item are the safest guide. If your favorite pan has seen better days, our guide to the importance of quality cookware covers what to look for in a replacement.

Hand washing isn’t a free pass either. Some things shouldn’t meet dish soap at all, so see our list of things you should never clean with dish soap. And if you’re on a roll, here are the foods you should never microwave.

The bottom line

Keep cast iron, kitchen knives and copper out of the dishwasher, and treat wooden boards, nonstick pans and insulated tumblers as check-first items. When a maker says hand wash, believe them. It takes a couple of minutes, and it’s the easiest way to make your best pieces last.