A normal sebaceous gland under high power. Towards the periphery of this single acinus of a sebaceous gland is a single layer of cuboidal cells that are somewhat deeper staining. Towards the center are large cells which are pale staining cytoplasm and a central pyknotic nucleus. At the very center is a dark staining structure that represents the duct of this gland. The central, light-staining cells are normally shed as such into the hair shaft and form the oily secretion that coats the hair as well as the overlying skin.
Sebaceous glands occur in most areas of the skin closely attached to the hair follicle.
Particular areas of skin such as the forehead and the area around the nose are particularly rich in sebaceous glands. Each gland is a fraction of a millimeter in diameter and consists of a large round acinus attached to the hair follicle by a very short duct. In cross section, the acinus has a single layer of cuboidal cells in the periphery and large empty looking cells with pyknotic nuclei towards the center. The larger cells are derived from the smaller cells by the accumulation of lipid. The empty looking cells, which are in fact filled with lipid, are shed into the hair shaft and empty on to the surface of the skin to give rise to the oily secretion characteristic of these glands.