The body naturally and continuously secretes sweat for thermoregulation during sedentary and routine activities at rates that can reflect underlying health conditions, including nerve damage, autonomic and metabolic disorders, and chronic stress. However, low secretion rates and evaporation pose challenges for collecting resting thermoregulatory sweat for non-invasive analysis of body physiology. Here we present wearable patches for continuous sweat monitoring at rest, using microfluidics to combat evaporation and enable selective monitoring of secretion rate. We integrate hydrophilic fillers for rapid sweat uptake into the sensing channel, reducing required sweat accumulation time towards real-time measurement. Along with sweat rate sensors, we integrate electrochemical sensors for pH, Cl−, and levodopa monitoring. We demonstrate patch functionality for dynamic sweat analysis related to routine activities, stress events, hypoglycemia-induced sweating, and Parkinson’s disease. By enabling sweat analysis compatible with sedentary, routine, and daily activities, these patches enable continuous, autonomous monitoring of body physiology at rest.

Wearable sweat sensors are emerging as promising platforms for personalized and real-time tracking of evolving health and fitness parameters. While most wearable sweat sensors focus on tracking biomarker concentration profiles, sweat secretion rate is a key metric with broad implications for assessing hydration, cardiac, and neural conditions. Here we present a wearable microfluidic sensor for continuous sweat rate measurement. A discrete impedimetric sensing scheme relying on interdigitated electrodes within a microfluidic sweat collector allows for precise and selective sweat rate measurement across a broad physiological range. Integration of a manually activated pressure pump to expel sweat from the device prevents sensor saturation and enables continuous sweat rate tracking over hours. By enabling broad range and prolonged sweat rate measurement, this platform tackles a key obstacle to realizing meaningful and actionable sweat sensing for applications in exercise physiology and medicine.

lying physical conditions that current devices may be unable to access. [3,[8][9][10] For example, sweat rate is important for the assessment and diagnosis of physical conditions like hyperhidrosis (excessive sweating) and hypohidrosis (lack of sweating) during sedentary or daily activities; it can also be used along with fluid intake quantities to assess the dehydration levels of athletes to maintain proper fluid balance and bodily functions. [11][12][13][14][15] Moreover, monitoring the rate of sweat production enables further analyses, as different sweat rates modulate the concentration of secreted analytes and are thus of critical importance for interpreting analyte concentration measurements. [16][17][18][19] Even though monitoring sweat rate has been studied tremendously in the past few years, only a few devices have become commercially available. [20,21] In addition, most of the new concepts are yet to be accepted by the medical field for consistent reliable health monitoring due to the requirements of safe and biocompatible build materials, comfortable geometry and form factor, and accessible and consistent mass production. [22][23][24] Traditional methods for monitoring sweat rate such as whole-body washdown and gravimetric pads are done off-body, in specialized settings, and with the intervention of trained Monitoring sweat secretion rate is essential for uncovering underlying physical conditions like hyperhidrosis, mental stress, and neural disorders. Often, flexible microfluidic sweat rate monitoring devices use tape as a means of attachment to the skin to tightly seal the collection area. While these single-use, adhesive-backed devices have lightweight and thin interfaces for mounting on the skin, their form factor complicates their potential integration with available commercial wearables, such as smartwatches. Here, a tape-free device, consisting of a 3D-printed sweat collector with a concave surface that is strapped onto the skin to form an effective seal, is presented. The materials, structure, and dimensions of the sweat collector are optimized for conformal device-to-skin contact and efficient capture of sweat. The collector is interfaced with a fluidic microchannel with embedded electrodes for continuous digital monitoring of sweat rate. Long-term exercise-induced local sweat rate from multiple body locations in both multi-subject and longitudinal studies is measured, depicting the correlation between the measured sweat profile and total body fluid loss. The simple installation procedure and reusability of this tape-free device make it a good candidate for integration with the band of a watch.