According to a recent report on ConsumerReports.org, here are seven things you shouldn't be cleaning in the dishwasher...
1. Nonstick cookware. Dishwashing soap is more abrasive than you think, and can scratch things up. So nonstick cookware doesn't hold up very well in the dishwasher.
2. Anything made of wood. Wood can warp or crack from the heat. Especially cutting boards. So when they need a deep clean, scrub them with baking soda instead.
3. Cast iron skillets. It ruins the "seasoning," which is what cast iron is all about. And it can make them rust. So it's better to just clean them right away with hot water.
4. Aluminum cookware. Even one dishwasher cycle can oxidize the metal and make them go from shiny to dull. Also, stainless steel pans are usually okay, but it depends on the brand.
5. Anything copper, like copper pots. Anything made of copper, silver, or gold will tarnish in the dishwasher. So don't put any family heirlooms in there either.
6. Certain plastic items. Look for "dishwasher safe" on the label, or check with the manufacturer. Just don't assume anything made of plastic is dishwasher safe. Some plastics can melt in there, or leach chemicals.
7. Sharp knives. The detergent dulls them over time. And the heat can loosen the handles. So always hand-wash them.