Epidermal nevus arises from a defect in the ectoderm and in general are due to an overgrowth of keratinocytes. Subclasses of epidermal nevus include Linear epidermal naevus, epidermolytic epidermal naevus, acantholytic epidermal naevus, linear porokeratosis, and systematised epidermal naevus. Several other conditions are also characterised by benign overgrowth of the epidermis and its appendages (organoid naevi), including inflammatory linear verrucous epidermal naevus, sebaceous naevus, sweat gland naevi, comedone naevus, and Becker naevus.