13 things you should never put in a dishwasher

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Whatever you do, don’t put any of these things in your dishwasher

Someone loading cutlery into a dishwasher
(Image credit: Shutterstock)

The best dishwashers are some of the most convenient appliances when it comes to washing up. They can clean pretty much anything you use on your dinner table, from plates and glassware, to cutlery. There’s even an extensive list of things you never knew you could wash in a dishwasher.

However, because of the intensity of the wash, there are certain objects you should never clean in a dishwasher. Whether it’s from the humidity or the detergent, one way or another, these items will take damage from your reliable dishwasher. Here are 13 things to avoid washing in a dishwasher. 

Also, if you want to save on your bills, here are 7 ways your dishwasher can save you money. Plus, here are 7 things to look for when buying a dishwasher. 

13 Things that should not go in the dishwasher  

1. Knives — We’re referring to chef’s knives here rather than tableware. Dishwashers are the worst thing for knives because the combined heat and humidity will likely damage them. It can lead to rust, corrosion and even warping, so stick to hand washing instead. Washing your knives in the dishwasher is one of the 7 mistakes which are ruining your kitchen knives. 

Knives aren't good news for your dishwasher either; check out how to make your dishwasher last longer for more on this.     

2. Wooden chopping boards — The extreme heat and moisture within a dishwasher will distort a wooden chopping board, causing it to warp and crack. For this reason, wooden utensils are another no-go for the dishwasher. 

Vegetables being prepared on a wooden chopping board

(Image credit: Shutterstock)

3. Nonstick pans — The nonstick surface on your favorite pan can be damaged by the severity of the dishwasher detergent and the high temperatures during the drying cycle. If anything comes into contact with your pan, that can also scratch away the nonstick. It may say dishwasher safe, but you could be doing more harm than good.  

4. Aluminium — Unless it’s been anodized, aluminium will be discolored and dulled during a dishwasher cycle. It will come out covered in a dark film, potentially with white spots from the dishwasher detergent, which will then transfer onto other items. Stick to hand washing again. 

5. Copper — Copper pans cost a hefty price and look beautiful on display. But, they can be tarnished easily by the harshness of a dishwasher. To keep your copper shining, hand wash it with a mild dish soap. 

A set of copper pans

(Image credit: Shutterstock)

6. Graters — Graters should not go in the dishwasher because, for one, there are so many holes that it’s difficult for the dishwasher to thoroughly clean the tool. And for two, the blades can cause damage to the plastic on the racks themselves, leading to rust. Carefully hand wash your graters for the best results and to protect your dishwasher.  

7. Cast iron — If you put exposed cast iron in the dishwasher, the harsh detergent will strip away the seasoning and leave it open to rust. If you need guidance on how to clean a cast iron skillet, we’ve got you covered. 

8. Anything insulated — If you’re putting your travel mug in the dishwasher, think again. The high heat of the wash can damage the insulated layer, leaving water trapped between the walls. The same can be said for insulated tumblers as well.

Regular mugs are fine, although if you find they're always coming out wet, this TikTok dishwasher hack will keep your mugs dry.

Someone wearing a white t-shirt holding and small travel mug

(Image credit: Shutterstock)

9. Pressure cookers lids — Some pressure cooker lids claim to be dishwasher safe, but these contain components which can be blocked by food particles during a wash, leading to a serious safety hazard. It’s imperative that these valves remain clear, so wash by hand instead. 

10. Fragile glassware or crystal — If it’s fragile then it really shouldn’t go in the dishwasher. The high temperatures and pressure from the cycle can chip and crack glass. Plus, the hard water can turn the glass cloudy, ruining it in more ways than one. Here's how to clean cloudy glasses if you've already encountered this problem.  

11. Fine china — Likewise, fine china really doesn’t belong in the dishwasher. This is especially the case if it’s been repaired, because the high heat can melt the adhesive. Things do move around in the dishwasher too, which can easily come into contact and cause damage.

A stack of china teacups

(Image credit: Shutterstock)

12. Anything with sticky labels — You can say goodbye to sticky labels once they’ve gone through a dishwasher cycle. The high heat and pressure will melt the adhesive and wash away any labels, leaving you to pick the remnants out of the filter. 

13. Thin plastic containers — Again, plastic containers may claim to be dishwasher safe, but if it’s particularly thin, it can be warped by the heat of the dishwasher. I’ve seen this to the point where the lid won’t fit anymore.

Katie Mortram
Katie Mortram
Homes Editor

Katie Mortram used to be a Homes Editor for Tom's Guide, where she oversaw everything from kitchen appliances to gardening tools, as well as smart home tech. Specializing in providing expert advice for cleaning and home manintenance, she now works as Household Advice Editor for Good Housekeeping.