Hyperkeratosis is thickening of the stratum corneum (the outermost layer of the epidermis, or skin), 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, also known as keratosis pilaris (KP), 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. When called phrynoderma the condition is associated with nutritional deficiency or malnourishment. 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. By other specific site Plantar hyperkeratosis is hyperkeratosis of the sole of the foot. It is recommended to surgically remove the dead skin, to provide symptomatic relief. Hyperkeratosis of the nipple and areola is an uncommon benign, asymptomatic, acquired condition of unknown pathogenesis. Hereditary Epidermolytic hyperkeratosis (also known as "Bullous congenital ichthyosiform erythroderma," "Bullous ichthyosiform erythroderma," or "bullous congenital ichthyosiform erythroderma of Brocq") is a rare skin disease in the ichthyosis family affecting around 1 in 250,000 people. It involves the clumping of keratin filaments. Multiple minute digitate hyperkeratosis, a rare cutaneous condition, with about half of cases being familial Focal acral hyperkeratosis (also known as "Acrokeratoelastoidosis lichenoides,") is a late-onset keratoderma, inherited as an autosomal dominant condition, characterized by oval or polygonal crateriform papules developing along the border of the hands, feet, and wrists. Keratosis pilaris appears similar to gooseflesh, is usually asymptomatic and may be treated by moisturizing the skin. Other Hyperkeratosis lenticularis perstans (also known as "Flegel's disease") is a cutaneous condition characterized by rough, yellow-brown keratotic, flat-topped papules. In mucous membranes The term hyperkeratosis is often used in connection with lesions of the mucous membranes, such as