Sweat (Perspiration): Function, Composition, Glands, and Health

Composition and visible properties

Sweat is mostly water but also contains electrolytes such as sodium and chloride, small amounts of urea and lactate, and trace organic compounds. The exact composition varies by gland type, body region, diet and hydration. Because of its salt content, dried sweat can leave white residues on clothing or skin. For more on chemical components and odor, see water content and salts and minerals. The smell associated with sweating often results from skin bacteria acting on secretions rather than the sweat itself; see why sweat can smell.

Types of sweat glands and distribution

Human skin contains millions of sweat glands distributed across most of the body. Two principal gland types are commonly described:

• Eccrine (merocrine) glands: Widely distributed, especially on the palms, soles and forehead, these glands produce a watery secretion that cools the skin as it evaporates.
• Apocrine glands: Found mainly in the armpits and groin, these glands secrete thicker fluid into hair follicles and become active at puberty; their secretions are more likely to produce body odor when broken down by bacteria.

The average person has millions of glands across the skin surface; they are absent on some specialized areas such as the lips, certain parts of the nipples and typically the external genital mucosa. For distribution details, consult sweat gland counts and regional notes at skin locations, including exceptions like the lips, nipples and some genital surfaces.

Cooling mechanism and triggers

Sweating cools the body chiefly through evaporative heat loss: when liquid sweat changes into vapor, it absorbs heat from the skin, lowering body temperature. The phase change process (evaporation) and the gas form of water are central to this effect; see evaporation and the concept of vapor. Triggers for sweating include environmental heat, physical exertion, hormonal changes, spicy food and emotional stimuli such as anxiety. The nervous system controls sweat production so responses can be rapid and region-specific.

Odor, hygiene and consumer products

Fresh sweat is often nearly odorless; the familiar body odor develops when skin bacteria metabolize sweat constituents, especially from apocrine areas. Personal hygiene and specialized products aim either to mask odor or to reduce sweating: deodorants primarily counter odor while antiperspirants reduce perspiration by temporarily blocking sweat openings. For distinctions and common approaches, see antiperspirants and deodorants and odor control. The pores through which sweat reaches the surface are important both for normal function and for some cosmetic or medical interventions; see skin pores.

Clinical considerations and cultural context

Both excessive sweating (hyperhidrosis) and deficient sweating (anhidrosis) can have medical consequences, from social discomfort to heat intolerance. Treatments range from topical agents and prescription medications to procedures for severe cases. Beyond medicine, sweat has cultural roles: in athletics, saunas, rituals and workplace contexts, sweating is associated with exertion, cleansing and stress. For general medical and societal perspectives, further reading is available through the sources linked above.

Notable facts and distinctions

Humans are particularly effective at evaporative cooling compared with many mammals because of widespread eccrine sweating and relatively hairless skin. Sweat composition and gland activity vary with age, sex, genetics and environment. When investigating sweat-related topics — from sports performance to clinical disorders — it helps to distinguish gland types, understand the evaporation process, and recognize the microbial role in odor formation.