Hyperkeratosis refers to the increased thickness of the stratum corneum, the outer layer of the skin, due to increased keratin production. The stratum corneum is composed of multiple layers of keratinocytes which, during maturation, produce keratin to protect the underlying skin cells. This overproduction of keratin is mainly caused by chronic physical or chemical damage, such as uneven friction and pressure or the use of harsh soaps, especially those with a basic pH, but can also result from chronic inflammation or as a side effect of various drugs, such as chemotherapy.
Hyperkeratosis can be classified as orthokeratotic, parakeratotic or a combination of both. Orthokeratotic hyperkeratosis refers to thickening of the keratin layer with preserved maturation of keratinocytes, whereas parakeratotic hyperkeratosis shows retained nuclei as a sign of delayed maturation of keratinocytes. The number and size of these keratinocytes, in combination with increased expression of adhesion molecules and decreased hydration make hyperkeratosis a recurrent pathology.
Hyperkeratosis depends on factors such as being overweight or practising sports associated with inadequate unloading or heavy work. It has a high incidence in adults (over 40 years of age) and is more frequent in women, for whom it represents an aesthetic and health problem, and in the elderly. It is estimated that 47% of the population suffers from some type of hardness or callus and 3 out of 4 people will develop this skin disease during their lifetime.
Although it can occur in any anatomical location, the palms of the hands, soles of the feet and elbows often have areas of hyperkeratosis. The most common forms of hyperkeratosis are calluses and corns. A callus is an area of thickened skin that usually appears on the feet, but can also grow on the fingers and elbows. Unlike a callus, a corn is usually uniform in thickness and does not hurt. A callus, on the other hand, is a lesion that usually develops on or between the toes, with a central lesion of very hard keratin and an outer ring of slightly softer hard tissue. While most calluses do not require medical attention (on hands and elbows), corns do need to be treated, as they must support the weight of our body and are painful.
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