The term ichthyosis (latin for “scaly fish dermatosis”) encompasses a wide range of various keratinizing disorders with different etiologies (Figure 8.1), but with the common feature of widespread epidermal hyperkeratosis and a dry and scaly skin (for a recent review see reference 1). Although acquired forms of ichthyosis exist (e.g., in association with malignancy, severe malnutrition, lepra, and treatment with lipid-lowering drugs), only the inherited forms will be discussed here.