To apologize for beginning with a ‘did you know that’ opening did you know that we sweat constantly without our knowing it? This is because sweating or perspiration is the human body’s way of maintaining an even body temperature and eliminating excess heat. As sweat evaporates from the body surface it has a cooling effect. Therefore we tend to sweat more when our bodies have been heated up either owing to a rise in temperature increased physical activity or nervous stimulation.
In humans sweat is secreted from two kinds of sweat glands: eccrine and apocrine. Though both are types of sweat glands the sweat that they secrete is not the same and neither is its purpose. And believe it or faint but the average human being has about four million sweat glands!
Eccrine sweat glands
When it comes to regulating body temperature eccrine sweat glands play a major role. These sweat glands are found all over the body but particularly concentrated on your palms soles and forehead. These areas consequently produce sweat composed chiefly of water along with small amounts of various salts. So in effect eccrine glands are used for body temperature regulation.
I just had to give you this bit of trivia straight out of a book I read: “Eskimos have made an environmental adaptation where they sweat less than Whites on their trunks and extremities but more on their faces. This adaptation allows for temperature regulation without the need to change clothes because of perspiration.” (Source: Transcultural Concepts in Nursing Care by MM Andrews and JS Boyle). So Eskimos sweat more on their faces and less on their palms and soles!
However I digress. Eccrine sweat glands are present mainly in the outer layer of our skin but also extend into the inner layer. The glands are under controlled by sympathetic cholinergic nerves which are in turn controlled by the hypothalamus (if you absolutely must know that’s the region of our brain that regulates metabolic processes and other autonomic activities). So it is the hypothalamus that senses a change in temperature both directly as well as from messages it receives from temperature receptors in the skin. Once it realizes the need for temperature regulation it modifies the sweat output. In effect it asks the body to cool down.
Apocrine sweat glands
Apocrine glands make their presence felt in our bodies during early to mid-puberty which means approximately around the ages of 12-15. Initially they release more than the normal amount of sweat and then settle down to regulate and release normal amounts of sweat after a certain period. Unlike eccrine glands the sweat from apocrine sweat glands contains fatty materials. Also unlike eccrine glands apocrine glands are concentrated in the underarms and around the genitals. It is with these glands that body odor is associated because apocrine sweat attracts bacteria that break down the organic compounds present in it and release the odor. Thus apocrine glands basically serve as scent glands.
While eccrine glands secrete more amounts of sweat during heightened physical activity or an increase in external temperature it is emotional stress that accelerates the production of sweat from apocrine glands. Also in some areas of the body apocrine sweat glands are modified to produce secretions that have nothing to do with sweat. Such ‘exceptional’ secretions include cerumen (earwax ugh) and milk in lactating women which comes from apocrine glands that have been greatly enlarged and modified.