Hard skin and callus are essentially the same things: a thickening of the skin.
What causes it? The way you walk, your shoes, your genetics. These are all factors in determining whether you are likely to have hard skin. Callus develops as a result of the body trying to protect itself from an unwelcome pressure point. Corns are a good example of this, but you can have a build-up of hard skin without necessarily developing a corn. For many people, the heels or on the ball of the foot are areas where callus appears.
What are the risks? Hard skin can build up to point where it starts to be painful. It can also crack, at which point you may develop fissures, particularly on the heels. These need to be treated as they can rupture and bleed, which provides an entry point for infection.
How can it be treated? The treatment is to remove the hard skin with a surgical blade. The skin is then sanded down and a specialist moisturiser is applied. For deep fissures, more than one treatment might be required.
Can I self-treat? The best thing you can do to keep hard skin at bay is to moisturise your feet as frequently as you can. This keeps the skin elastic, and delays the build-up of callus. Moisturise, moisturise, moisturise…
InStep Foot Health 