I worked for a Medical Software company as a tech - we had to replace keyboards so often at some offices because of this, we would leave spares.
Then there was the keyboard we had to replace because the space bar would not go down anymore. We brought it back to the office and opened it up and there was so much makeup in the keyboard, it had built up under all the keys and was causing most of them to not go down very far, and the spacebar to stick. We placed a discreet call to the Office Manager who confirmed for us the lady that worked there put her makeup on at her deskevery morning - right over the keyboard. ugh, that's just yucky.