Sweating is a normal reaction of the body to exercise. Although much of sweat is water, there are many other components. These components can be an indication of the condition of the athlete. Increase of elements and salts in the tissue will also work their way through to the sweat. Measurement directly in tissue can be an excellent indicator, but a non-invasive approach is simpler to use and safer. Concentrations in sweat can also be an indication that the athlete is in danger of collapse. This paper looks into the components in sweat and how this change with exercise. The aim is to develop a simple, wearable system able to warn the athlete of the impending danger and prevent a potential accident.@en