Capacitive switches are completely free of wear and tear, and in some applications can be a valuable asset to machine designers and operators. Their mode of operation is fundamentally different to that of mechanical switches because there is no stroke and there are no moving parts either. Simply touching the sensor area with the finger alters an electrical field which in turn triggers a change of the switch state. All this happens without any pressure on the sensor: a better understanding of the subject can be gained by taking a look at a new document just published by Schurter.
This link White Paper CPS will take you straight to it.