Whenever skin is exposed to repetitive stress – such as direct pressure, or shear forces, it responds by either forming an acute blister, or – with time – a callus. Calluses occur frequently on the foot because of footwear and weight-bearing pressure. Calluses are more appropriately defined as hyperkeratosis – that is, a thickening of the outer layer of the epidermis of the skin.
Calluses occur in other places – such as the finger tips of guitar players. Again, this is a response to repetitive pressure on the skin.
When the forces through the skin are higher or more frequent, then tissue layers deeper to the skin can become affected. This can lead to problems such as bursitis or capsulitis within the foot. If the forces are still unremitting, the hardest tissue – bone – can be affected, giving rise to problems such as stress fractures.
Many people wonder why a corn or callus will keep coming back in the same part of the foot. Generally, this is because this is where the force is greatest – usually in association with a bony prominence or joint. Therefore, although removing a corn or callus is very simple and painless, preventing it coming back is a lot harder.
This is where altering the tissue stress and forces comes into play. Podiatrists use various techniques to achieve this; from simple things such as footwear changes, through to orthotics and splints, right through to surgical procedures to permanently alter the forces. Once enough pressure has been reduced through the skin with any of these approaches, then the problem will usually settle over a few months – and hopefully not occur again.