The secretion of sweat — perspiration — in humans serves as a mechanism for the excretion of some waste products and, more importantly, for regulating body temperature.
Two types of sweat glands can be found in the skin of humans: eccrine glands and apocrine glands.
An average sized person has about 2.5 million sweat glands distributed over much of the body. When the body is stressed it is capable of producing as much as 1 to 2 quarts of sweat in an hour.
The cooling effect on the body is not just sweat dripping from the skin, rather the cooling comes from the actual evaporation of the sweat from the skin surface. Hence, when the body temperature rises due to hot weather, illness or excessive muscle exertion, the sympathetic nervous system stimulates the eccrine sweat glands to secrete sweat. This will lower the core body temperature by evaporative cooling.
Men tend to sweat up to twice as much as women. Both sexes tend to sweat less with age. Sweat is about 99 percent water and is basically odorless. However, it does contain small amounts of dissolved salts and a variety of organic compounds. Various species of bacteria on your skin can use these compounds to grow and reproduce, and in the process, produce a variety of waste products. Some of these products are volatile and very smelly which can lead to body odor.
Although eccrine glands are found over most of the body, apocrine glands are fewer in number and generally located in areas covered with hair such as the armpits and genital region. The body produces only small amounts of apocrine perspiration, but it is responsible for much of the body odor produced. It tends to be high in the organic molecules that bacteria on the skin are able to utilize.
The abundant eccrine sweat tends to spread the apocrine fluid over a larger area of the body along with the odorous by-products of bacterial activity. Each human has a unique sweat fingerprint that results from a blend of some 370 volatile compounds found in sweat. These remain fairly consistent over time. Therefor, regardless of your health, feelings, or diet, your sweat is distinctly yours. This can allow a dog with a keen sense of smell to readily pick you out of a crowd.
Larrie Stone is a retired Dana College science professor.