Keratinocytes are cells that make up most of the epidermal (outer) layers of the skin and make keratin, a fibrous protein. Keratin is a structural protein that gives skin, hair, and nails their hardness and waterproof properties.
The stratum corneum is the outermost layer of the skin and the most keratinized for protection. This layer will reactively thicken with increased pressure and shearing, but can also thicken due to inherited characteristics. Callous is a thickening of the stratum corneum and occurs most frequently on the soles of the feet and palms of the hand. Callouses can be broad and diffuse or discrete lesions. Callouses on the bottom of the foot that are chronic or just show up and persist are not uncommon.
Painful callouses are the driving force for many podiatry visits. Callouses can be the result of skin aggravation from ill-fitting shoes or develop from forces generated from exercise or work requirements.
However, callouses can also be inherited. Removal of the irritant for pressure callouses will lead to reduction in callous, but does not help with inherited callouses, which are not the result of an irritant.
Inherited characteristics are a common cause of callous that stumps many people. Abnormal thickening of the skin is called keratoderma. Symptomatic keratoderma usually affects the soles or palms. Discrete lesions that arise on pressure areas, referred to as corns by laymen, and cracks called fissures are common reason for podiatric visits as these generally cause discomfort or outright pain.
Inherited keratoderma is either dominant or recessive and is caused by an abnormal keratin gene. Dominant forms tend to occur in every family member if both parents are affected. Children have a 50% chance of the gene if only one parent is dominant. Recessive forms will only be passed on to children if each parent has the recessive gene.
People with the recessive gene will not have inherited callouses, but can be considered “carriers.” Recessive forms lead to patient confusion in my experience because they do not know relatives with the issue. Patients want to know why this happen to them and when they are told it is inherited, they tend not believe this as they do not know of a family member that is affected.
Regardless of the origin, painful callouses can be relieved by shaving/removing and/or offloading pressures. However, inherited callouses will return at some point, regardless.
David B. Raynor, DPM, is a podiatrist in Inverness and can be reached at 352-726-3668 or at www.AdvancedAnkleAndFootCenters.com with questions or suggestions for future columns.