Callous formation can also be pathological
Unfortunately, in addition to the natural form of hard skin formation, the elimination of which is the major topic of Mr. Fuss and this website, there is also pathological hard skin formation. In fact, there are also changes in the stratum corneum that have pathological or at least abnormal causes.
Generally, the medical profession calls this keratosis, more simply put, it is called a keratosis disorder.
Unnatural thickening - Hyperkeratosis
In hyperkeratosis, the uppermost corneal layer thickens more than average.
This is divided into 2 subtypes. Like you here there are two essential aspects that make up the natural process of dead skin formation. On the one hand, it is the original cell division (formation) of the keratinocytes, which later change into the corneocytes (corneocytes). On the other hand, it is the scaling of the corneocytes on the skin surface.
If there is excessive cell division and thus the release of more keratinocytes, this is called proliferation hyperkeratosis.
The second subtype of hyperkeratosis as pathological dead skin formation is retention hyperkeratosis, and this is referred to when the recoating of the epidermis is disturbed.
There are different causes for these disorders. In addition to external influences, e.g. through exposure, but also through environmental toxins such as arsenic or UV radiation, genetic predisposition or metabolic changes are also identified as the reason for this pathological dead skin formation.
Irregular development of the cell kernel - Parakeratosis
A different form and also pathological dead skin formation is present when the cell kernel of the keratinocytes irregularly do not lose their nuclei during the usual process of change, but instead retain them.
Here the physician speaks of parakeratosis. This parakeratosis is seen, for example, in psoriasis or eczema.
Hyperparakeratosis - the combination
When both clinical pictures meet, this is called hyper-para-keratosis.