The epidermis is made up of several strata or layers. The cells with a reproductive capacity are located in the innermost layer called the basal layer. As they multiply, these cells reach the surface and are filled with keratin (a structural protein of the skin, hair and nails). When they reach the outermost layer or stratum corneum, they are eliminated (flaking process). So, in a period of 6 to 8 weeks the skin cells have been completely renewed.
When there is an increased production rate in the cells or a reduction in elimination rate, this causes a thickening of the stratum corneum, which is known as hyperkeratosis.
Why does hyperkeratosis occur?
Hyperkeratosis is generally a defence mechanism to avoid damage to the innermost layers of the skin. For instance, it can be due to constant rubbing and irritation, as is the case of hardness or calluses on the hands and feet; infections, such as warts; chronic eczema or dry skin; chronic inflammation as in the case of psoriasis, where psoriatic plaques originate; genetic disorders, such as ichthyosis, etc.
How does hyperkeratosis manifest itself?
Hyperkeratosis is asymptomatic in most cases. Although eczematous skin may cause itching and hardness, calluses and warts may cause pain. A common problem with hyperkeratosis is the aesthetic aspect.
Hyperkeratosis sometimes manifests as:
- Calluses: A callus is an area of thickened skin that usually occurs on the feet, but it can also grow on the toes.
- Eczema: This condition causes skin redness and itching that can appear in scattered plaques or as small bumps.
- Warts: These appear when the skin is infected with one of the viruses of the human papillomavirus (HPV) family. Although they can grow anywhere on the skin, they most likely appear on the hands or feet.
- Psoriasis: a chronic inflammatory disease that manifests with reddish scaly lesions that typically appear on the elbows, knees and scalp and that can also affect the nails and joints.