Hereditary or inherited ichthyoses are monogenic disorders of cornification due to mutations in genes involved in the skin barrier function. Skin changes involve most of the tegument, and are characterised by scales of various forms and severities. They are often associated with erythema. The classification should be clinically based, and distinguishes syndromic from nonsyndromic ichthyoses. The diagnosis of the form of ichthyosis is usually very difficult.

Palmoplantar keratodermas comprise a diverse group of hereditary disorders marked by excessive thickening of the epidermis of palms and soles. They are genetically heterozygous. The diagnosis of the form of palmoplantar keratoderma is usually very difficult and there is no curative treatment. The treatment is mainly symptomatic (local or systemic) and usually not effective enough and burdensome. They are rare conditions with no sexual or racial predominance which start at birth or in infancy.