Epidermolytic ichthyosis (EI), formerly known as epidermolytic hyperkeratosis (EHK) or bullous congenital ichthyosiform erythroderma (bullous CIE), is one of the five main types of congenital ichthyosis. EI is rare, and affects approximately 1 in 100,000 individuals worldwide. It affects males and females in equal numbers. EI presents at birth with erythroderma, blisters, and erosions and evolve over time into varying degrees of hyperkeratosis. It can be categorized into two types; PS-type and NPS-type. Patients with the PS-type have palmoplantar or palm/sole hyperkeratosis, in addition to other areas of the body. Patients with the NPS-type, on the other hand, do not have extensive palmoplantar hyperkeratosis, but do have hyperkeratosis on other areas of the body.

Diagnosis is based on the clinical features and on histological examination of skin lesion biopsies showing hyperkeratosis with orthokeratosis, hypergranulosis, and cytolysis in the upper stratum spinosum and granular layers. Treating EI is a challenge; emollients are often used but their efficacy is limited. EI can be life-threatening during the neonatal period due to infections and/or dehydration.

EI is inherited in an autosomal dominant pattern, with about 50% of cases representing spontaneous mutations. Mutations in the KRT1 (12q13.13) or KRT10 (17q21-q23) genes are known to cause epidermolytic hyperkeratosis. These genes encode proteins called keratin 1 and keratin 10, which are found in cells called keratinocytes in the epidermis. Mutations in these genes impair keratin intermediate filament formation in the suprabasal keratinocytes. The position of the mutation may influence the severity of the phenotype; KRT1 gene mutations are associated with PS-type epidermal hyperkeratosis, while KRT10 gene mutations are usually associated with NPS-type.