You know that you sweat when you feel hot, whether due to the temperature of your surroundings or a hard workout at the gym. You may also sweat when you're nervous because emotions can trigger chemical reactions in the body. What you might not know is precisely what's going on in your body to make you sweat and why it's known as a particular type of chemical reaction.

Sweat is merely a mixture of water, sodium and other cooling substances. Your body has two types of sweat glands: thousands of eccrine glands throughout the entire body and apocrine glands mainly in the underarm and groin areas. When the body’s temperature goes up, the nervous system stimulates the eccrine glands to release sweat.

Apocrine glands are triggered by stress, anxiety and hormones. These glands create bacteria to help disperse the sweat, which sometimes leads to body odor. This explains why you only apply deodorant to your armpits and not all over your body.

On average, people have 2 to 4 million sweat glands. Many things, including gender, genetics, age, fitness level and environmental influences, determine how much sweat each gland releases. Two of the biggest sweat rate factors are weight and fitness level. A person who weighs more is likely to sweat more because the body uses more energy to function, and there is greater body mass to cool down.

Most chemical reactions and changes in a physical state involve breaking or forming chemical bonds. It takes energy to break a chemical bond, but forming a chemical bond produces energy. The two types of chemical reactions are known as endothermic and exothermic reactions.

An endothermic reaction takes place when a system takes energy from its surroundings. The system gains heat as the surroundings cool down. Examples of endothermic reactions are electrolysis, melting ice cubes and evaporating liquid water.

An exothermic reaction takes place when heat flows out of a system into its surroundings. The system loses heat, and the surroundings heat up. When you sweat, the system – your body – cools down as perspiration evaporates from the skin and heat flows to the surrounding area. This means sweating is an exothermic reaction. Other exothermic reactions are nuclear explosions, the rusting of steel, and the reaction between sulfuric acid and table sugar.