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.