It's a common misconception that knives are suitable for cleaning in the dishwasher. The truth is, the dishwasher is considerably more aggressive in its action than cleaning by hand.  Highly concentrated cleaning agents, long periods in hot steam and even the residue of certain kinds of food can lead to spots or corrosive actions on the knife blade. It is recommended cleaning knives by hand, using a soft cloth and mild cleaning agent. After cleaning, the knife should be carefully wiped dry to avoid spotting of the blade.

Certain handle materials, and designs also make dishwashers a bad choice for cleaning. Wood handle knives can experience swelling and deterioration from prolonged exposure to water.  Some poly handle knives, especially those that have riveted handles or handles compressed onto the blade, can experience expanding (both in the handle and blade)—creating gaps and loose fits.

Extreme hot water can also affect the tempering on some blades, making the edge soft.

When storing your knives, use a knife block, magnetic knife holder, drawer storage system, wall mounted knife rack, case, blade guard, or store any other place where blades will not rub against each other.

Other Recommendations:

Clean after each use—the quicker you remove materials from the blade, the better.

Do not allow knives to lie in water for long periods of time, or sink where other cooking utensils will rub against the blade.

Avoid using knives (other than cleavers) to cut through bones or frozen foods.

Cut only on wooden or polyethylene cutting boards. Hard surfaces such as laminates, tile or stainless steel can damage blades.

Sharpen knives regularly, as directed.