Ichthyosis refers to a collection of skin disorders that result in dry, rectangular scales resembling fish scales. The term originates from the Greek word "ichthys," meaning fish. Different metaphors are often used to describe the skin's appearance and texture in the various types and stages of ichthyosis, such as alligator skin, crocodile skin, collodion skin, porcupine skin, and, naturally, fish skin. Most forms of ichthyosis are genetic, being passed down through families. However, some types can develop alongside other systemic diseases or be a key feature of specific genetic syndromes. The term "ichthyosis" is frequently used on its own to denote ichthyosis vulgaris.Ichthyosis vulgaris, or ichthyosis simplex, is inherited in an autosomal (non-sex-linked) manner and is marked by scaly skin that resembles fish scales. The initial appearance of these scaly skin issues typically occurs after the age of 3 months. Commonly affected areas include the palms and soles, while regions like the armpits, the inside of the elbow bend (antecubital fossa), and the area behind the knee (popliteal fossa) are often spared. The gene implicated in ichthyosis vulgaris is located on chromosome band 1q21. It is believed that the product of this gene is a substance known as filaggrin (FLG for short), which may serve as the "matrix protein" within the cells of the stratum corneum, a layer of the skin.
