Apparently you can learn a lot about a person from his/her sweat! Sweat contains a great number of electrolytes and metabolites and although normal values for many of these components in sweat are not available, it may simply be because sweat has never been considered as a body fluid that can be used as a diagnostic tool. Recently, materials scientists developed wearable electronics that have the ability to continuously analyze the composition of sweat and transmit the data wirelessly to a smart phone.
The current instrument can measure body temperature as well as the concentration of glucose, lactate, sodium and potassium in sweat. The technology has obvious applications in athletics, but also in the medical field. It also opens new avenues for research as it has now become necessary to do research on the normal levels of metabolites and electrolytes in sweat. It is also necessary to investigate the accuracy of these levels at a clinical level.
Summarized by:

Marlise van Staden (PhD, Physiology)
University of Limpopo

Reference:
Geddes, L. 2016. Wearable sweat sensor paves way for real-time analysis of body chemistry, Nature (27 January 2016).