Dishwashers are harsher than hand washing: hotter water, aggressive detergent, prolonged exposure and high-pressure jets. Most items survive it and several categories do not, and the damage is usually gradual rather than immediate.
Why Dishwashers Damage Things
Dishwasher detergent is strongly alkaline and contains abrasive components. Combined with sustained heat, it etches surfaces, dulls finishes, degrades adhesives and softens plastics over repeated cycles.
The result is rarely a single dramatic failure. It is a wooden handle that has split after two years, a nonstick pan that has lost its coating, or glassware that has gone permanently cloudy.
Generally Safe
- Stainless steel, though polished finishes dull over time
- Borosilicate and tempered glass, in most cases
- Glazed ceramic and stoneware without metallic decoration
- Most modern plastics rated for it, on the top rack
- Silicone, which is entirely unaffected
Glass storage with removable silicone gaskets is straightforward here, provided the seal is removed and washed separately. Canister ranges with clamp lids, of the kind catalogued by oggi, generally specify care per component, since the glass, the gasket and the metal clamp have different requirements.
Generally Not
Wood, which swells, splits and loses its finish. Cast iron, which loses its seasoning and rusts. Good knives, where the detergent dulls the edge and the handle suffers. Nonstick, where the coating degrades faster than hand washing.
Also: anything with a hollow handle that traps water, copper and brass, anodised aluminium, which discolours permanently, and anything hand-painted or with gold decoration.
The Cloudy Glass Problem
Glassware that goes permanently cloudy is a common complaint, and there are two different causes.
Limescale deposits are removable, and a soak in white vinegar restores clarity. Etching, caused by soft water combined with too much detergent, is permanent damage to the glass surface and cannot be reversed.
Using less detergent, particularly in soft water areas, prevents the second. Most people use considerably more than needed.
Loading Sensibly
Items that nest block water from reaching each other, which is why a badly loaded machine produces dirty dishes and people conclude the machine is failing.
Face soiled surfaces toward the spray arms, do not overlap, and check that the arms rotate freely before starting. Anything lightweight belongs on the top rack where it will not be blown about.
Maintenance
Filters clog, and a clogged filter recirculates dirty water. Cleaning the filter monthly is the single most effective maintenance and the one most consistently skipped.
A hot empty cycle with a machine cleaner periodically clears grease from the interior and the drain, which is where the smell comes from when a machine develops one.
When in Doubt
Check the item rather than assuming. Manufacturers generally state care requirements, and a minute of checking is cheaper than a ruined pan.