Pumice is a natural porous lave stone. Soften skin with warm soapy water. A foot bath first is ideal. Wet the stone and massage lightly over callused areas to remove dead skin.
Don't press too hard and be cautious if you're diabetic. Do not use on broken or irritated skin. Stop immediately if you your skin feels sensitive or sore.
Dead skin cells do build up in the pores of the stone. Use an old toothbrush to brush the stone with soap and water after each use. You can also boil the stone to ensure you've killed any bacteria build up. Replace often.