Skin glands are specialized structures embedded within the skin that perform functions necessary for the body’s protection and temperature regulation. They produce and secrete various substances onto the skin surface or into hair follicles, maintaining the body’s external barrier. These secretions preserve skin moisture and establish a mild antimicrobial environment.
Sebaceous Glands and Sebum Production
Sebaceous glands are typically found in association with a hair follicle, forming a structure known as the pilosebaceous unit. These microscopic glands are distributed across most of the body, with the highest concentration appearing on the face and scalp. They are absent only on the palms of the hands and the soles of the feet. The primary product of these glands is sebum, a complex, oily, and waxy substance.
Sebum production utilizes a unique mechanism called holocrine secretion, which involves the complete disintegration of the secretory cells. Cells within the gland, called sebocytes, mature by accumulating large amounts of lipid droplets until they rupture. This process releases the entire cellular contents, including the cell remnants and the synthesized oil, into the gland’s duct. The sebum then travels up the hair follicle and spreads onto the skin surface.
The composition of sebum includes various lipids, such as triglycerides, wax esters, squalene, and free fatty acids. This oily coating acts as a natural lubricant for the hair shaft and the skin’s surface. It creates a waterproof barrier that minimizes water evaporation, preventing the skin from drying out. The slightly acidic nature of the sebum contributes to the skin’s acid mantle, offering defense against certain types of microorganisms.
Sweat Glands: Eccrine and Apocrine Functions
The body possesses two primary types of sweat glands. Eccrine sweat glands are the most numerous, distributed over almost the entire body surface, with the highest density on the palms, soles, and forehead. These glands open directly onto the skin’s surface through a coiled duct, and their primary function is thermoregulation.
Eccrine glands secrete a clear, watery substance that is mostly composed of water, with small amounts of sodium chloride and other electrolytes. When the body temperature rises, the secretion of this sweat allows for evaporative cooling, which is the most effective mechanism for lowering internal body heat in humans. The production of eccrine sweat is primarily controlled by the sympathetic nervous system in response to thermal or emotional stimuli.
In contrast, apocrine sweat glands are largely confined to specific areas of the body, such as the armpits, groin, and around the nipples. Unlike eccrine glands, apocrine glands typically empty their secretions into the upper part of the hair follicle, rather than directly onto the skin. These glands become active only after puberty, stimulated by hormonal changes.
The secretion from apocrine glands is thicker and more viscous than eccrine sweat because it contains organic compounds, including proteins and lipids. This fresh secretion is initially odorless, but it serves as a nutrient source for the bacteria residing naturally on the skin. The subsequent breakdown of these organic compounds by surface bacteria generates body odor. While their function in humans is not primarily for cooling, they play a role in chemical signaling.
When Skin Glands Malfunction
Dysfunction in skin glands can lead to several common dermatological conditions. Acne vulgaris represents a frequent sebaceous gland malfunction. The condition involves the overproduction of sebum, often stimulated by hormonal shifts, particularly androgens. This excessive oily material combines with dead skin cells to create a plug within the hair follicle.
This blockage forms a non-inflammatory lesion, known as a comedone, which can be either a blackhead or a whitehead. When this environment becomes colonized by the anaerobic bacterium Cutibacterium acnes, an inflammatory response is triggered. This leads to the formation of red, swollen lesions, such as papules, pustules, or the deeper nodules and cysts characteristic of more severe acne.
A common malfunction of the eccrine sweat glands is hyperhidrosis, which is excessive sweating. Primary focal hyperhidrosis involves bilateral and symmetrical excessive sweating in specific areas like the palms, soles, or armpits. This condition is not caused by heat or exercise but results from the overstimulation of eccrine glands by faulty nerve signals.
Another notable malfunction is bromhidrosis, characterized by an offensive body odor. This condition is often linked to the apocrine glands, where the bacterial breakdown of their protein-rich secretions is heightened. Bromhidrosis can also be associated with eccrine sweat, particularly when the sweat softens keratin, leading to bacterial degradation that produces an unpleasant smell.