Acquired disorders of keratinization are a heterogeneous group of diseases, clinically characterized by dyskeratosis. This may involve a spectrum of presentations ranging from the soft velvety changes of acanthosis nigricans to the hard dry scaling of Flegel disease or the porokeratoses. The symptoms are often discrete, and while many of the diseases are poorly described, some show an association with other diseases, indicating the need for additional clinical investigations, e.g. the association between phrynoderma and malnutrition or porokeratosis and cancer. Because of the rarity of many of these disorders, treatment recommendations are frequently based purely on small observational studies: commonly advocated treatments include emollients, vitamin D derivatives or retinoids. The aetiopathogenesis of most of these disorders remains unexplored.

Keywords acquired ichthyosis, acanthosis nigricans, confluent and reticulate papillomatosis, pityriasis rotunda, keratosis pilaris, lichen spinulosus, keratosis circumscripta, phrynoderma, trichodysplasia spinulosa, Flegel disease, multiple minute digitate keratosis, porokeratosis, transient acantholytic dermatosis, keratolysis exfoliativa, xerosis cutis and asteatosis, acute epidermal distension, acute oedema blisters