Skin glands

Skin glands are specialized exocrine structures embedded within the dermis and hypodermis of the skin that produce and secrete various substances essential for maintaining cutaneous homeostasis, thermoregulation, protection, and lubrication. They are broadly classified into the following types:

Sudoriferous (Sweat) Glands

These glands are responsible for producing sweat and play a critical role in thermoregulation and excretion. They are subdivided into two types:

• Eccrine glands: Found 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, watery fluid (sweat) 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 by cholinergic sympathetic nerve fibers and are functional from birth.

• Apocrine glands: Located primarily in the axillae, groin, periareolar region, and perianal area. They are larger than eccrine glands and 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 odoriferous when metabolized by skin bacteria. Apocrine glands become active at puberty and are regulated by adrenergic sympathetic innervation. A specialized variant, the apoeccrine gland, has been described in the axillary region and shares features of both eccrine and apocrine glands.

Sebaceous Glands

Sebaceous glands are holocrine glands found throughout the skin, except on the palms and soles. They are most abundant on the face and scalp. These glands are typically associated with hair follicles, forming the pilosebaceous unit, although free sebaceous glands exist on the lips (Fordyce spots), eyelids (meibomian glands), and genitalia. They produce sebum, a complex lipid mixture composed of triglycerides, wax esters, squalene, cholesterol, and cholesterol esters. Sebum lubricates the skin and hair, provides a hydrophobic barrier, has antimicrobial properties, and delivers antioxidants (such as vitamin E) to the skin surface. Sebaceous gland activity is primarily regulated by androgens.

Ceruminous Glands

These are modified apocrine glands located in the external auditory canal. They produce cerumen (earwax), a waxy substance that, combined with sebaceous secretions, protects the ear canal by trapping debris, repelling water, and providing antimicrobial defense.

Mammary Glands

Although functionally distinct, mammary glands are considered modified apocrine sweat glands of the skin. They are specialized for the production of milk (lactation) and are regulated by a complex hormonal milieu including estrogen, progesterone, prolactin, and oxytocin.