Sweat glands

Sweat glands are exocrine glands found in the dermis and subcutaneous tissue of the skin that produce sweat (perspiration) and play a critical role in thermoregulation, electrolyte balance, and skin surface protection. There are two main types:

Eccrine Sweat Glands

Eccrine glands are the most abundant type, distributed across nearly the entire body surface with the highest density on the palms, soles, and forehead. They are simple, coiled tubular glands that secrete a hypotonic, odorless fluid composed primarily of water and sodium chloride directly onto the skin surface via a duct that opens at a sweat pore. Their primary function is thermoregulation through evaporative cooling. Eccrine glands are innervated predominantly by sympathetic cholinergic nerve fibers and are functional from birth.

Apocrine Sweat Glands

Apocrine glands are larger glands concentrated in the axillae, groin, periareolar region, and perianal area. Their ducts open into hair follicles rather than directly onto the skin surface. They produce a viscous, lipid-rich secretion that is initially odorless but becomes malodorous when metabolized by skin surface bacteria. Apocrine glands become active at puberty and are primarily regulated by adrenergic (sympathetic) innervation. They are believed to play a role in scent signaling rather than thermoregulation.

Apoeccrine Sweat Glands

A third type, apoeccrine glands, has been described in the axillary region. These glands share features of both eccrine and apocrine glands and develop from eccrine-like precursors during puberty. They may contribute significantly to axillary sweating.

Histological Structure

Both eccrine and apocrine glands share a general architecture consisting of a secretory coil (located deep in the dermis or at the dermal-subcutaneous junction) and a duct that transports secretions to the surface. The secretory portion of eccrine glands contains clear cells (which secrete water and electrolytes) and dark cells (which secrete glycoproteins), surrounded by myoepithelial cells that aid in expulsion of sweat.