Sweat diagnostics is an emerging non-invasive technique used to provide insights to the health of the human body.  Common sweat diagnostic tests include testing for cystic fibrosis and illicit drugs.  Most testing of human sweat is in reference to the eccrine sweat gland which in contrast to the apocrine sweat gland, has a lower composition of oils.
Although sweat is mostly water, there are many solutes which are found in sweat that have at least some relation to biomarkers found in blood.  These include: sodium (Na), chloride (Cl), potassium (K), ammonium (NH), alcohols, lactate, peptides & proteins.  Development of devices, sensing techniques and biomarker identification in sweat continues to be an expanding field for medical diagnostics and athletics applications.
The use of smart biosensors for on-skin sweat analysis has been described as internet-enabled Sudorology (iSudorology) by Brasier et al. in 2019. It describes the lab-independent detection of molecular, next-generation digital biomarkers in sweat.