Compound naevus. Light micrograph of a section through a compound naevus, a type of skin mole. This pigmented naevus is produced by abnormal clustering of pigment cells (melanocytes) in the skin. At top are loose cornified layers on the surface of the skin composed mostly of the protein keratin (red). Beneath this is the pink epidermis made up of layers of cells. Below centre are clusters of melanocyte pigment cells of the dermis with many purple nuclei. These dermal pigment cells form the compound naevus. Like other moles, naevi are harmless, but on rare occasions can become cancerous. Haemotoxylin & eosin stained. Magnification: x2.5 at 35mm size.