Abstract

Hyperkeratosis is thickening of the stratum corneum (the outermost layer of the epidermis), often associated with the presence of an abnormal quantity of keratin, and also usually accompanied by an increase in the granular layer. As the corneum layer normally varies greatly in thickness in different sites, some experience is needed to assess minor degrees of hyperkeratosis.

It can be caused by vitamin A deficiency or chronic exposure to arsenic.

Hyperkeratosis can also be caused by B-Raf inhibitor drugs such as Vemurafenib and Dabrafenib.

It can be treated with urea-containing creams, which dissolve the intercellular matrix of the cells of the stratum corneum, promoting desquamation of scaly skin, eventually resulting in softening of hyperkeratotic areas.

Types | Follicular

"Follicular hyperkeratosis" dass (also called "phrynoderma") is a skin condition characterized by excessive development of keratin in hair follicles, resulting in rough, cone-shaped, elevated papules. The openings are often closed with a white plug of encrusted sebum.

This condition has been shown in several small-scale studies to respond well to supplementation with vitamins and fats rich in essential fatty acids. Deficiencies of vitamin E, vitamin A, and B complex vitamins have been implicated in causing the condition.

Hyperkeratosis of mucous membranes

The term hyperkeratosis is often used in connection with lesions of the mucous membranes, such as leukoplakia. Because of the differences between mucous membranes and the skin (e.g. keratinizing mucosa does not have a stratum lucidum and non keratinizing mucosa does not have this layer or normally a stratum corneum or a stratum granulosum), sometimes specialized texts give slightly different definitions of hyperkeratosis in the context of mucosae. Examples are "an excessive formation of keratin (e.g., as seen in leukoplakia)" and "an increase in the thickness of the keratin layer of the epithelium, or the presence of such a layer in a site where none would normally be expected."

Etymology and pronunciation

The word "hyperkeratosis" () uses combining forms of "" + "" + "", conveying "the condition of too much keratin".