Fig. 5

Sweat-triggered chemesthetic feedback. a A liquid menthol solution resides in a semicircular channel that defines the chemesthetic reservoir. Scale bar: 1 cm. b Sweat enters into the collection channel as air pressure is relieved through the shunt channel. c The contact of sweat with the citric acid/sodium bicarbonate foaming agent produces CO₂ which ejects the menthol. d After filling the collection channel, sweat enters into a reaction chamber. As the sweat fills beyond a set of containment pillars in this chamber it encounters a foaming agent tablet to initiate a reaction that forms CO₂ gas, thereby producing pressure that ejects the liquid menthol. The small cross section of the shunt channel (25 × 250 µm) prevents significant flow through the shunt. Scale bar: 1 cm. e Rate of ejection of a menthol solution. The error bars indicate standard deviation. f Ejection of 14 mg of menthol solution elicits a sensation within 10 min of ejecting for 9/12 subjects. g Ejection of 38 µg of capsaicin elicits a response within 10 min of ejecting for 12/16 subjects. NS = no sensation.