A dishwasher combines three stresses: hot water, harsh detergent, and a high-heat drying cycle — with the bottom rack getting the most of all three. That’s why “top rack only” is such a common instruction, and why some items that survive a rinse still shouldn’t go in.
What the dishwasher does to things
- Heat warps thin plastic. The drying element and the lower rack run hottest, so heat-sensitive items go on the top rack, away from it.
- Detergent is abrasive and alkaline. It strips seasoning off cast iron, dulls knife edges, and can pit aluminum.
- Water gets into places it shouldn’t. Insulated mugs, wooden handles, and sealed items can trap water and degrade.
- Look for the symbol — a dishwasher-safe mark (dishes or glasses under water droplets), often with “top rack” noted.
Common items in the dishwasher
| Item | Verdict | Why / condition |
|---|---|---|
| Stainless steel | Safe | Handles heat and detergent well. |
| Cast iron | Unsafe | Detergent strips the seasoning and it will rust. |
| Most modern plastics (#5) | Conditional | Top rack only, away from the heating element. |
| Aluminum (bare) | Conditional | Can discolor and pit; anodized handles it better. |
| Wood / bamboo | Unsafe | Absorbs water, then warps and cracks. |
| Glass / ceramic dishes | Safe | Usually safe; hand-wash delicate or gold-trimmed pieces. |
Per-item and per-brand dishwasher pages — including which rack and which cycle — are being added. Suggest one and we’ll get to it.
General guidance — check your label. Verdicts here are based on manufacturer specs, USDA/FDA guidance, and material science, but individual products vary by line and generation. Always defer to the symbol or care instructions printed on your specific item. When in doubt, don’t heat it.