2 types - one are simply a circle of foam that adheres to the skin and redistributes the pressure from the corn, which is placed in the centre - the hole. They are OK because that is all they do, redistribute pressure. The second which claim to be medicated and are often referred to as carnation pads, although Scholl and other people make them, work by releasing a caustic agent onto the skin/corn. Granted they may work occasionally, but more often than not damage the surrounding tissues to the extent that any effective treatment has to be postponed. Go and see a Chiropodist and have it manually reduced. Takes seconds and is painless.