There are two main types of secretions from the skin: sebum and sweat. The sebaceous glands secrete sebum, an oily substance that is excreted from the hair follicles. Sweat is secreted through one of two glands: eccrine or apocrine. Sebaceous glands are holocrine glands, while sweat glands are merocrine glands.
Merocrine secretions are products of exocytosis, where secretions travel from secretory cells into the epithelial duct, and then into the lumen. Holocrine secretions are produced in the cytoplasm of cells and are secreted into the lumen when the plasma membrane is ruptured. Eccrine glands secrete odorless sweat through pores in the skin, while apocrine glands secrete odorous sweat through hair follicles.