Folks, this is disgusting. I had to replace this keyboard just the other day, and I really felt like I needed a hazmat cleaning afterward. The reason it was replaced was because the letters on the keycaps were fading. I know this means it was in use for a long time, but please, this is not necessary.
Also, PLEASE DO NOT LOOK AT THIS IF YOU MIGHT FEEL QUEASY OR LOOSE YOUR LUNCH!
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Something witty, part deux 
add two table spoon of white vineger in half a cup of lukewarm water, damp a cotton cloth in it (not too wet) wipe your key board and between keys, switch off your power supply first.