Praise be to Allah, the Lord of Creations, and Peace and blessings be upon our prophet Muhammad, the faithful and the honest. 
 Oh, Allah, we know nothing but what You teach us. You are the All- Knower, the Wise. Oh Allah, teach us what is good for us, and benefit us from what You taught us, and increase our knowledge. Show us the righteous things as righteous and help us to do them, and show us the bad things as bad and help us to keep away from them. 
  O Allah our Lord, lead us out from the depths of darkness and illusion, unto the lights of erudition and knowledge, and from the muddy shallows of lusts unto the heavens of Your Vicinity.

Cooling system in the human body, its components and function 

 The human body is divinely equipped with a marvelous cooling system, which some scientists call “Perspiration System”, which does the work of cooling, air conditioning, and heat-control of the human body. 
 This system consists of 1,000,000 cooling units, i.e. sweat-glands. A sweat gland consists of a pipe 2 millimeters long and 1\10 millimeter in diameter. This pipe curls round itself and is linked with the skin. These pipes scatter equally all around the surface of the skin, but they are more numerous in such parts as the forehead, foot-sole, palm, and other parts of the body, with an average of 300 sweat-glands in each centimeter. Each sweat-gland is a complete cooling apparatus. If these million pipes were linked together, they would be 5 kilometers long.  

In each 100 grams of the sweat produced by these cells there are 99 grams of water and one gram of solvents, half of which is salt and the second half is made up of uric acid and other chemicals. Every 24 hours, man produces from 600 to 1000 grams of sweat. The process of perspiration is constant, but we do not feel sweat unless it is excessive. Skin softness and dampness are considered as  evidence of the  continuity  of perspiration.  

In other words, without perspiration the skin would not be soft or damp. Moreover, perspiration is considered as a safety valve for the body temperature, just like the safety valve that protects pressure pots from exploding due to great internal pressure. This applies to the human body: if its temperature rose excessively, man would soon die. That is why there is a safety valve to control the temperature of the human body. No sooner does the internal body temperature rise  than the sweat glands begin producing sweat that evaporates, absorbs the heat and causes the temperature to drop, keeping the skin temperature within normal limits. 

 Among the great many functions of perspiration are: expulsion of uric acid, softening of skin, and controlling the body temperature. 
 One should Care   to wash the body in order to remove unpleasant  odours of perspiration. This is because in our human body there are salts and uric acid, just as in urine. That is why it has been rightly said:  

“Wash your body even if a Mudd (approx. one liter of water) costs a Dinar.” 

 In fact, Friday Major Ablution (i.e. washing of the whole body) in Islam is considered  a religious obligation in order to remove unpleasant  deposits   of perspiration; and it is Allah’s Right on a Muslim to wash his body once a week, as confirmed by the Messenger of Allah, (PBUH). Narrated Jabir that the Messenger of Allah, (PBUH), said:  

“A Muslim has to perform Major Ablution (wash his whole body) every Friday.” 

[Narrated by Ahmad (14305) and Ibn Shaibah (5007)] 

 And cleanliness is the fruit of true faith, because washing   the whole body removes the   unpleasant smell of perspiration and its unpleasant  deposits  after sweat has evaporated. It also opens pores of the skin and sweat-glands.