The skin glands, like hair and nails, originate as inward growths of the epithelium into the dermis of the skin. Types of skin glands in humans are categorized as either sebaceous glands, or sweat glands.
The sebaceous glands are branched alveolar (sac-like) glands which are typically associated with hair follicles. Their secretions consist of debris from cast off cells and their oily contents. This material is called sebum and it provides the hair and the skin surface an oily covering for conditioning and protection. The tarsal glands are large sebaceous glands on the eyelid margin. The glands of Zeis are sebaceous glands associated with the eyelashes.
The typical sweat glands (eccrine sweat glands, merocrine sweat glands) of the skin surface are unbranched tubular glands with a highly coiled basal portion. In the coiled base there are secretory cells surrounded by a loose basket of thin myoepithelial cells. Contraction of the myoepithelial cells forces secretions from the deeper part of the duct to rise to the surface.
Apocrine sweat glands have a similar structure to eccrine glands, but are larger and have a more viscous secretion. They become active at puberty and are found in the regions of the axilla, groin, and areolas.
Ceruminous glands are glands of the ear canal that combine with sebaceous secretions to produce ear wax. They resemble typical apocrine sweat glands in structure.
Special apocrine glands of the eyelid margin are called the glands of Moll.
Mammary glands are branched tubular milk producing glands. Several glands develop in association with each nipple. The development of these glands beyond embryonic formation is under hormonal control. Some growth of these glands occurs in females after puberty. Extensive growth of glands and ducts occurs in pregnancy, and active secretion begins after giving birth.