When the body is hot, blood vessels in the skin dilate to increase blood flow and allow perspiration in order to regulate the temperature. However, when we sweat a lot, we lose body fluid. When the level of body fluid falls, body temperature rises, and we face the risk of overheating.

When you lose body fluid equivalent to just 2% of your body weight, you feel thirsty and your body’s ability to perform starts to fall. When you lose 3%, you get very thirsty, and experience symptoms such as feeling faint and suffering a loss of appetite. When you lose 4% to 5% of your body weight, you experience dehydration symptoms such as fatigue, headaches and dizziness. Finally, if you lose 10% or more of your body weight, there is a risk of death.