Corns and Callous are generally the result of excessive pressure and commonly occur under the ball of the foot, the periphery of the heels and over the digits.
The excessive pressure is detected by cells within the body that respond by producing skin at a much faster rate in an attempt to build up a protective barrier.
Callous is hard skin that has developed in a more diffuse or widespread fashion, as opposed to a Corn which is much more focused over a smaller area such as the ball of the foot, and has a central core called the nucleus.
Callous may give rise to a burning sensation under the forefoot and heel as the hard skin creates greater pressure on the small underlying nerves and blood vessels. This results in a temporary and minor interference to the circulation in that area and once the pressure is relieved there is a sudden influx of blood (known as hyperaemia) which give rise to the hot burning sensation.
Corns are often more painful than callous as the nucleus lie deep within the skin, pushing on underling nerves and bone prominences.
Callous and corns generally occur where foot posture and toe deformities create localised pressure. Your podiatrist may recommend treatment directed at reducing pressure, most commonly with footwear changes, Orthotics to correct foot posture and silicon pads and shields.
There are a few medical conditions that may result in excessive skin production such as Palmoplantar keratoderma, that require dermatological referral and specific medical treatments.