Figure 1.

a) Block diagram showing the two routes for achieving energy‐autonomous/self‐powered wearable systems for sweat monitoring along with key devices. b) The major anions and cations present in sweat. c) The general scheme of a sweat‐based health monitoring system showing the flexible patch with multiple sensor to analyze various analytes in sweat and sweat‐based energy generating (BFC) and storage (SC) devices, the smart tag with electronic for data acquisition, power management, control circuitry for automated sweat extraction and finally the wireless powering (via NFC) and wireless data transmission to portable gadget, such as smartphone. The data in (b) are from ref. ^{[ 83 ]}. Image of NFC enabled smart phone and cloud in (c): Adapted with permission.^{[ 40 ]} Copyright 2020, The Authors, published by The American Association for the Advancement of Science.