Evaporation-Induced Clogging of an Artificial Sweat Duct.

Metal-based antiperspirants have been in use for centuries; however, there is an increasing consumer demand for a metal-free alternative that works effectively. Here, we develop an artificial sweat duct rig and demonstrate an alternative, metal-free approach to antiperspiration. Instead of clogging sweat ducts with metal salts, we use a hygroscopic material to induce the evaporation of sweat as it approaches the outlet (i.e. pore) of the sweat duct. As a result, the sweat dehydrates almost completely while still being inside of the duct, forming a natural gel-like salt plug that halts the flow. We show that the critical pressure gradient within the duct (∼3 kPa), beneath which clogging occurs, can be rationalized by balancing the mass flow rates of the liquid (Poiseuille's law) and the evaporative vapor (Fick's law).