Our skin produces sweat (also called perspiration), which is watery, when the body becomes hot. The sweat glands found beneath the skin surface produce sweat, which appears from the sweat pores - minute holes present in our skin. Sweat mostly comprises water along with some amount of salts.

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Sweat is produced by the skin to calm down the high body temperature. When sweat evaporates from the surface of the skin, it draws the excessive heat from the body. In addition, some amount of our body waste is also removed by sweat.

Precisely speaking, sweat is our body's own mechanism to make itself cool when it becomes hot, irrespective of whether the excess heat is caused owing to rigorous actions of the muscles or from invigorating the nerves excessively. On average, an individual possesses numerous sweat glands (as many as 2.6 million) in his/ her skin. In fact, all parts of our body, barring the lips, exterior genital organs and nipples, have a uniform number of sweat glands. The skin layer where the sweat glands are found is known as the dermis. In addition to the sweat glands, the dermis also has additional 'equipment', for instance hair follicles, nerve endings and many others.

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Structurally, the sweat glands are basically elongated, twisting void tubes made up of cells. Sweat is produced in the coiled or twisted portion of the sweat gland within the dermis and the elongated portion is actually a conduit that joins the sweat glands to the sweat pore or opening on the external surface of the skin. Even the nerve cells belonging to the autonomic or sympathetic nervous system are lined to these sweat glands.

The sweat glands can be categorized into two types - eccrine and apocrine.

Eccrine sweat glands: This type of sweat glands are found in plentiful numbers throughout the human body, especially on the forehead, the palms of our hands as well as the soles of our feet. Between these two types, eccrine sweat glands are comparatively small and on the go since birth. These sweat glands make sweat that does not contain any protein.

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Apocrine sweat glands: This type of sweat glands is generally present in our armpits (also called axilla) and the area in the region of the anus and external genital organs. In comparison to the eccrine sweat glands, these are larger and they generally end up in the hairs instead of the sweat pores. Moreover, the apocrine sweat glands do not become active till one attains puberty.

How sweat is made

Although we might not be aware of it, we sweat continuously. In fact, sweating or perspiration is one of the main means by which our body eliminates excessive body heat that is generated during working the muscles or metabolism. The amount of sweat made by our body is subject to our emotional state as well as the physical activity we undertake. In addition, sweat may also be produced as a reaction to the stimulation of the nerves, work-outs undertaken by an individual and/ or temperature of hot air. Let us first concentrate on the manner in which an eccrine gland produces sweat.

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Invigoration of the eccrine sweat gland results in the cells releasing a fluid (also called primary secretion) which is somewhat akin to plasma. In other words, sweat mostly comprises water, but also contains elevated levels of sodium as well as chloride and a poor potassium concentration, but does not contain any protein or fatty acid, which is generally present in plasma. This fluid originates in the interstitial spaces (the gaps among the cells) that receive this watery substance from the capillaries (blood vessels) present inside the dermis. This fluid passes from the twisted part of the sweat gland and by means of the long duct to reach the external skin surface. The activities inside the long conduit are dependent on the amount of the production or flow of sweat. The activities that may follow inside the straight duct are as follows:

Low sweat production (caused by cool temperature and rest): Cells that comprise the long hollow duct of the sweat gland again take up nearly all the sodium as well as chloride present in the watery fluid. This occurs as there is sufficient time for the cells to reabsorb these salts. Besides, water is also soaked up again through a process known as osmosis. As a result of this, very little sweat actually reaches the external surface of the skin. In addition, the constituents present in the sweat that comes out of the sweat pores in the skin are notably dissimilar from what is known as primary secretion. This sweat does not contain sodium as well as chloride in their earlier concentration, and now it has additional amounts of potassium.

High sweat production (caused by hot temperature and exercise): There is not much time for the cells that make-up the long and hollow section of the sweat gland to once again soak up the entire sodium plus chloride contained in the watery liquid released by the eccrine sweat glands (primary secretion). As a result of this, copious amounts of sweat reaches the external surface of the skin through the sweat pores and its constituents are also more or less, but not precisely, the same as that of primary secretion. The concentrations of the two salts (sodium as well as chloride) is roughly 50 per cent less, while that of potassium is approximately 20 per cent more to what was present in the primary secretion.

The same mechanism is followed to produce sweat in the apocrine glands. Nevertheless, in addition to sodium, chloride and potassium, sweat produced in the apocrine sweat glands encloses proteins as well as fatty acids, making the sweat more congealed and impart a milky or yellow hue. This is the main reason why our clothes are stained yellow. In fact, on its own, sweat does not have any smell, but when the proteins and fatty acids present in the sweat are metabolized by the bacteria as well as the hair present on the skin's surface, it emits a disagreeable odour. This is the main reason why we mainly apply deodorants to our underarms and not the entire body.

It is worth mentioning here that the highest amount of sweat produced by an individual not acclimatized to hot climatic conditions can generate is roughly one litre every hour. It is amazing to note that provided you travel to a region having a hot climate, for instance the tropics or southwest of the American desert, you will be able to produce much more sweat, approximately 2 to 3 litres every hour, just within roughly 6 weeks. In fact, apparently this is the highest volume of sweat that an individual can make in an hour.

Function of sweat

As the sweat disperses into gaseous form from the skin's surface, it also gets rid of surplus heat from the body and calms it down. In effect, this happens owing to a precise rule in physics - that goes something like this. In order to transform water from its liquid form into a vapour, it requires some amount of heat, which is known as 'heat of vaporization'. This heat is a specific form of energy that enhances the water molecules' pace to enable them to disappear into the atmosphere. The value of this energy for water is 540 calories per gram (also measured as 2.26 x 106 joules per kilogram). Hence, if you are able to generate one litre of perspiration that is equivalent to 1 kg or 1,000 grams (the density of water being 1 kg per litre or 1 gram/ ml) in an hour, you can get rid of heat having the value of about 540,000 calories from the body. In fact, this is an example of the utmost volume of sweat that an individual is able to produce. Usually, the entire sweat produced by the body does not fade away, but instead flows from your skin. Moreover, our body does not lose the entire energy produced by it by means of sweating. Some amount of energy is radiated directly from your skin into the air, while some other is lost by means of the lungs' external respiratory surfaces.

The relative humidity of the atmosphere where you are is one main aspect that has an effect on the evaporation rate. In case the atmosphere is damp, it contains water vapour from before, possibly to the point of saturation, and, hence, is not able to absorb any further amount. As a result, it is not possible for the sweat to evaporate and make your body cool as fast and well as it would have done when the atmosphere is arid.

After the water content of the sweat has evaporated, it leaves behind the salts (chloride, sodium and potassium) on the skin and this is the reason behind the salty taste of your skin after perspiration. The downside of sweating is that if your body loses plenty of water and salts through sweating, it has the aptitude to make you dehydrated very fast, often resulting in health disorders like problems related to blood circulation, heat stroke and kidney failure. Therefore, when you are outdoors in elevated temperatures or when you work-out, you ought to drink lots of fluids. It may be noted that various sports drinks available in the market enclose some of the salts to substitute for what has been lost through sweating.

The good side of sweating is that it helps our body to control its temperature. In fact, sweating is regulated from a center located inside the anterior and preoptic regions of the hypothalamus in the brain, where you will find the thermosensitive nerves. The response from the temperature receptors present in our skin also influences the role of the hypothalamus in regulating heat. Elevated temperature levels of the skin lower the set point of the hypothalamus for perspiration and augment the response from the feedback system of the hypothalamus to changes in the basic temperature. However, in general, the response of sweating to any increase in the hypothalamic (also called 'core') temperature is a great deal larger compared to the reaction to similar rise in the average temperature of the skin.

When we perspire it results in a decline in the hypothalamic temperature by means of cooling due to evaporation at the surface of the skin. When the molecules containing elevated levels of energy (in other words, molecules having high temperatures) disperse from the surface of the skin and release energy that has been taken up from the body, the temperature of our skin as well as the superficial vessels drops. Subsequently, the temperature of the cooled blood circulating through the veins also reverts to the core or hypothalamic temperature of the body and neutralizes the increasing core temperatures.

In fact, the nerves normally invigorate the sweat glands under two situations resulting in perspiration. These two situations are when there is some kind of emotional stress and at the time of physical heat. Generally, sweating brought about by emotional stress is limited to the armpits, palms of the hands, soles of the feet and occasionally the forehead, whereas perspiration induced by physical heat takes place all over the body.

Sweat composition

It needs to be underlined that though sweat is watery, it is not wholesome water, but contains some amounts (about 0.2% to 1%) solute. When any individual shifts from a cold climatic region to a region having a hot climate, his/ her sweating mechanism undergoes some changes to adapt to the new situation. This process of change is known as acclimatization. For instance, in such cases, the maximum amount of sweat that the individual can produce increases, while the amount of solute in the sweat decreases.

In addition, the amount of water that is lost through sweating every day varies to a great extent, alternating from 100 ml daily to about 8,000 ml daily. On the other hand, the loss of solute through perspiration may be as high as 350 mmol daily (or about 90 mmol daily when the individual has acclimatized) of sodium in very severe conditions. On average, an individual may lose up to two litres of body water in an hour while undertaking exercises of usual intensity. When the climatic condition is cold and the individual does not exercise, he/ she may lose as less as below 5 mmol of sodium every day. The intensity of sodium in sweat is anything between 30 mmol per litre to 65 mmol per litre subject to the extent of acclimatization.

Sweat primarily consists of water, in addition to some amount of minerals, urea and lactate. The composition of minerals in sweat differs from one individual to another, depending on his/ her degree of acclimatization; their ability to adapt themselves to heat; the specific source of stress (for instance, sauna and others); work-outs and sweating; the period of perspiration as well as the mineral components in their body. Under normal circumstances, the composition of minerals in the sweat is like this - sodium 0.9 g/ litre), calcium (0.015 g/ litre), potassium (0.2 g/ litre) and magnesium (0.0013 g/ litre). In addition to these, several additional trace elements are also lost through sweat. While it is possible that the measurements will differ by 15 times, under normal situations their concentration in sweat is like this - zinc (0.4 mg/ litre); iron (1 mg/ litre), copper (0.3 mg/ litre to 0.8 mg/ litre), nickel (0.05 mg/ litre), chromium (0.1 mg/ litre), and lead (0.05 mg/ litre).

It is very likely that several other trace minerals that are present in the body in much less concentration may also be lost by means of sweating in equally fewer amounts. A number of exogenous organic amalgams also get into the sweat as shown by an unknown having an odour similar to that of compounds having the scent of maple syrup present in different species belonging to the mushrooms of the Lactarius genus. In the instance of humans, perspiration is hypo-osmotic compared with plasma (in other words, it is less saline).

Why does sweat smell?

When we sweat we not only get wet, but also feel somewhat sticky. But just don't hold your sweat glands responsible for the unpleasant smell when you do a little running around outdoors.

On its own, sweat does not have any smell. In effect, when the bacteria that sustain on the surface of your skin mix with perspiration, it emits a horrible smell. After an individual attains puberty, he/ she secretes specific hormones that have an effect on the sweat glands located in the armpits - the sweat glands located in this part of the body produce sweat that actually smells foul.

Fortunately, we are generally able to contain the horrible smell by washing ourselves with soaps regularly. Several teens as well as adults may also find that applying deodorants or antiperspirant lotions is also helpful in getting rid of such stinky smell.

Therefore, you should not be concerned over sweating a little, because it is absolutely normal and every individual perspires. Although it seldom occurs among children, at times excessive sweating may possibly be an indication that something is not normal in your body. Provided you notice that you are perspiring excessively, it should normally be an indication of the fact that you should begin to use some good antiperspirant lotion or deodorant. However, in case you suspect that you are having a problem related to sweating, it is advisable that you either discuss the issue with your parent or consult your physician regarding the problem.


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