Sweating

Sweat is produced by sweat glands found in the skin of mammals including human beings. It comprises series of folded up tubules with cells that produce sweat. Also in the sweat gland are cells that can contract to push out sweat produced. Sweat passes out of the gland through the sweat duct on to the skin where it performs its functions.

At all times, we lose water from our skin by evaporation which we are not aware of. This is called insensible water loss or insensible perspiration. The clear secretion produced by sweat glands called sweat is also called sensible perspiration or sensible water loss because we are aware of it.

Sweat is mostly water (99 percent), but it does contain some electrolytes (chiefly sodium chloride), metabolites, and waste products. The presence of sodium chloride gives sweats a salty taste.

Sweat cools the surface of the skin and reduces body temperature. By this it performs a very important function of cooling the body and preventing overheating which can lead to death as the human body cannot survive beyond a certain body temperature.

Thus, when the body's temperature rises above a certain level, receptors in the body sense it and send messages to the brain. The brain then sends messages to the sweat glands in the skin to produce sweat. Blood vessels to the skin open up and a lot of hot blood gets to the skin. Water in the sweat produced takes up this heat and evaporates producing a cooling effect on the skin and the blood. By so doing, the whole body is cooled down.

The dog has very few sweat glands on its skin and produces very little sweat. To overcome this disadvantage, it opens its mouth wide and sticks out the tongue in order to expose a large area of the mouth and throat to the air. Water in the mouth and throat evaporates to help cool it down.

Since sweat produces contains some mineral and waste substances, sweating can be regarded as a form of excretion as these substances are removed from the body. Thus, exercises or activities that make you sweat a lot also help you to eliminate salts and metabolites from your body.

Sweating is also protective against environmental hazards. Sweat dilutes dangerous chemicals that the body may be exposed to and prevents the growth of certain germs. It is however important to note that sweat that is left on the skin for a long time (not bathing) can promote the growth of some other germs.

It is not only heat that can cause the production of sweat. Emotional states can also do likewise. These include anxiety, stress and tension. However, emotionally induced sweating is generally restricted to palms, soles, and sometimes the forehead, while physical heat induced sweating occurs throughout the body.

There are between 2 to 4 million sweat glands in the body. Sweat glands may be grouped as apocrine or eccrine (also called merocrine).

Apocrine sweat glands are found in axilla (underarm or armpit), perianal (near the anal area), areole (area around the nipple), periumbilical (around the belly button or navel), genital area, external ear canal and eyelids. These glands have ducts which empty into the canal from which hair grows. They do not empty directly onto the skin.

Sweat produced by apocrine glands is thick and cloudy in nature because it contains in addition to the normal contents of sweat; proteins, ammonia and lipids. Bacteria found where apocrine glands are, especially the armpit and genital are able to decompose these proteins to produce a characteristic odour or smell in these areas. This accounts for the body odour that occurs in persons with poor personal hygiene practices.

Eccrine or merocrine sweat glands are found in the skin on the rest of the body but the most concentration is found in the palms and soles. Estimates are that the palm of the hand has about 500 glands per square centimetre (3,000 glands per square inch). No wonder the palm can sweat so much.

Eccrine glands secrete an odourless, clear fluid that helps the body to control its temperature by promoting heat loss through evaporation.

In people who have excessive sweating, or hyperhidrosis, the sweat glands (eccrine glands in particular) overreact to stimuli and are just generally overactive, producing more sweat than is necessary. It's often said that people with hyperhidrosis have sweat glands that are stuck in the “on” position.