Sweat Glands

Sweat glands, technically called sudoriferous glands, are coiled secretory structures embedded in the dermis that release fluid onto the skin. They are essential for temperature control and come in two main types, eccrine and apocrine, which differ in location, what they secrete, and how their fluid reaches the surface.

Eccrine Glands

Eccrine glands are the most numerous and are found over almost the entire body, with the highest density on the palms, soles, and forehead. Each consists of a coiled secretory portion deep in the dermis and a duct that opens directly onto the skin surface through a pore. Eccrine glands produce a watery, odorless sweat made mostly of water and salt. Their primary job is thermoregulation: when body temperature rises from exercise, heat, or fever, these glands release sweat that evaporates and cools the skin. They are controlled by the sympathetic nervous system.

Apocrine Glands

Apocrine glands are larger, roughly ten times the diameter of eccrine glands, and are limited to specific regions: the armpits (axillae), anogenital area, areola, and external ear canal. Rather than opening onto the skin directly, they empty into hair follicles. Apocrine glands are dormant until puberty and produce a thicker, protein- and lipid-rich secretion. This fluid is initially odorless, but skin bacteria break it down to create characteristic body odor. A related variant, apoeccrine glands, is found in the axillae.

How They Secrete and Clinical Relevance

Both gland types secrete in a merocrine fashion (by exocytosis), though apocrine glands also pinch off bits of cell membrane in a process historically called "decapitation." Clinically, excessive sweating is called hyperhidrosis, while the inability to sweat (anhidrosis) raises the risk of dangerous overheating. Blocked or inflamed apocrine glands contribute to hidradenitis suppurativa, and eccrine duct blockage causes heat rash (miliaria). Sweat chloride testing is also a key diagnostic for cystic fibrosis. This content is educational and not medical advice.