We control our body temperature by perspiring (from Latin words meaning "to breathe through") or sweating (an Anglo Saxon word that means just what it says). When you're warm or tense, your sweat glands begin their work of cooling you off. One set of these glands, the eccrine glands (sometimes called the "true" sweat glands), covers most of the skin. They're especially dense on the forehead, face, palms, soles and armpits, and they secrete a slightly acidic, very dilute solutions of inorganic ions (largely sodium, potassium, and chloride), lactic acid (CH₃-CHOH-CO₂H), some urea (H₂N-CO-NH₂) and a little glucose. The cooling effect of sweating comes from the evaporation of the water from this secretion, which ordinarily has no odour.

       Another set, the apocrine glands, releases a different kind of substance, one that can easily become disagreeable. Like the sebaceous glands, which occur wherever hair grows, these apocrine glands lie almost exclusively under the arms, in the groin, and in a few other smaller regions of the body. While their secretions produce little or no odours in themselves, bacteria that accumulate in the nearby strands of hair can degrade the contents of the apocrine fluids into foul-smelling products.

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