The human body cools itself by evaporation. When sweat evaporates, it removes heat from the skin. Sweat contains water and salt which are pushed out of pores in the skin by blood vessels.
The body loses a lot of moisture through sweating so we need to drink liquids regularly in order to replace the fluids lost. Sweating is controlled by the hypothalamus.
When we are hot, the hypothalamus sends a signal to the sweat glands which causes them to release sweat onto our skin. The moisture in this sweat evaporates and cools us down.
If your body temperature is high then sweating will not be enough to keep you cool so you will also feel hot. This is because the hypothalamus will send a signal to the sweat glands and blood vessels telling them to reduce their activity so that you do not overheat.
Sweat is salty which helps us maintain our water balance in two ways: The saliva produced in the mouth has an alkaline reaction (this means it is slightly basic). This helps to neutralize acids that are produced in your stomach.
The body needs various chemicals called electrolytes (e.g. sodium and potassium) for certain processes such as the movement of muscles, nerves, etc.
Sweating is an important way of removing these substances from the body so that it does not become too acidic.
Sweating and body temperature are linked so that sweating is increased when the body heats up but reduced if the body cools down.
This helps to keep our internal environment at a constant level of heat which we call homeostasis.