Sweat glands are small, tubular structures embedded in the skin that produce and secrete sweat. Distributed across almost the entire human body, their primary function is thermoregulation: keeping the body’s temperature within a narrow, healthy range. These exocrine glands also perform several other roles that contribute to overall skin health and bodily homeostasis.
The Two Types of Sweat Glands
The human body possesses two distinct types of sweat glands: eccrine and apocrine. They differ significantly in structure, location, and the composition of the fluid they release.
Eccrine glands are the most numerous and are distributed widely, with the highest densities found on the palms, soles, and forehead. These glands open directly onto the skin’s surface and produce a clear, watery, and odorless secretion primarily made of water and electrolytes.
Apocrine glands are confined to areas with hair follicles, such as the armpits and groin. They release a thicker secretion containing lipids, proteins, and carbohydrates into the hair follicle, becoming active only after puberty.
The distinct odor associated with perspiration results from skin bacteria metabolizing these organic compounds from apocrine sweat. Apocrine glands are activated primarily by emotional stress rather than heat, and their role in cooling is minor.
Primary Role in Thermoregulation
The central role of sweat glands is regulating core body temperature, a function performed almost entirely by the eccrine glands. When internal temperature rises, the hypothalamus detects this change and signals the eccrine glands to begin secreting sweat. The glands are innervated by the sympathetic nervous system, which uses the neurotransmitter acetylcholine to initiate the sweating process.
This cooling mechanism relies on the physical process of evaporative cooling. Sweat is secreted onto the skin’s surface, and as this liquid changes state to a gas, it absorbs a significant amount of heat energy from the body. This heat dissipation effectively lowers the temperature of the skin and the blood flowing beneath it, cooling the entire core.
The efficiency of this process is heavily influenced by air humidity. In high humidity, the air is saturated with water vapor, which slows the rate of sweat evaporation and reduces the body’s ability to cool itself. The eccrine glands also actively reabsorb some sodium and chloride, helping to conserve these electrolytes, though this can be overwhelmed during intense sweating.
Secondary Functions Beyond Cooling
While temperature control is the primary task, sweat also helps the body with excretory and protective functions. Eccrine sweat contains small amounts of metabolic byproducts, including urea, lactic acid, and various electrolytes. This serves as a supplementary route for eliminating trace waste, though the kidneys remain the primary organ for detoxification.
Sweat contributes to the skin’s defense system by forming the acid mantle, a slightly acidic film on the skin surface. This low pH environment inhibits the growth of certain bacteria and fungi. Eccrine sweat also contains antimicrobial peptides, which support the immune system against potential invaders.
Apocrine sweat, while not involved in cooling, may play a role in chemical communication. The compounds in these secretions potentially carry chemical signals linked to emotional or social responses.
Common Issues and Disorders
When sweat glands malfunction, it can lead to disorders involving either excessive sweating or the inability to sweat.
Hyperhidrosis is defined by sweating that exceeds what is physiologically necessary to maintain normal body temperature. This overactivity can be localized to specific areas like the palms and armpits, or generalized across the body, often causing discomfort.
Anhidrosis is the inability to produce sufficient sweat when the body needs to dissipate heat. This condition is serious because it severely impairs the body’s ability to cool down, placing the individual at high risk for heat-related illnesses such as heat stroke. Anhidrosis can result from nerve damage, certain medications, or clogged sweat ducts.