The skin is made up of layers: the epidermis is the outer surface layer and the dermis a dense fibrous tissue which lies beneath. Deeper subcutaneous tissues composed mainly of fat cells provide protection against heat and cold, pressure and other forms of injury. Skin thickness varies over different parts of the body with the thickest in the soles of the feet.
The outer epidermal cells are composed of keratin and are replaced every 28 days when they naturally shed. The process is known as keratinization (or cornification) and is modified by environmental factors such as pressure and friction. The cells of skin on the soles and palms contain far more keratin than the skin on other parts of the body.
When the outer layers of skin are subjected to general mechanical stress this causes the skin to thicken protectively. The localized thickenings of the skin, i.e. callus or hyperkeratosis, formed is painless. When the skin surfaces are subjected to more intense intermittent pressure and friction this causes painful callus.
Prolonged complex ‘cork screw tension’ across skin surfaces especially over bony prominences results in more painful corn formation. Outwardly, the corn appears to be growing from a core or root. Pain is due to the thickened mass transmitting pressure to sensitive nerve endings within the surrounding subdermal tissues. Only certain skin types have a built-in predisposition to produce hyperkeratotic plaques, hence not everyone has problem hyperkeratosis and the reason for this remains unknown.
Pain relief comes from removal of excess skin usually with a sharp scalpel. However, this is almost impossible to do safely for yourself and needs an expert (podiatrist) to do this on your behalf. Anyone with failing eyesight, or those coping with reduced blood supply to the feet, or suffer systemic disorders like diabetes mellitus should never attempt self-treatment. In the case of chronic corns treatment options are palliative and not corrective, routine skin reduction will however, relieve symptoms. In any case, successful outcome is dependent upon removal of all external shearing stress.
Corn paints and medicated plaster should be avoided as these products may contain acids which can prove hazardous to those with poor circulation or impaired immune response. Non-medicated padding may bring temporary relief.