Extended Data Fig. 1: Fabrication of the custom Ecoflex earpiece used for sweat mapping.

a. The modeling clay was inserted and pressed gently inside the ear to obtain the inner shape of the participants. Next, the clay with the shape of the inner ear was removed from the participants. b. After removal, the clay with the inner ear canal shape was sprayed with mold release. Afterward, the piece was placed inside a receptacle in which a mixture of Ecoflex mixture was poured. Next, the receptacle and its content were dried at 65 °C for 15 minutes. c. After drying, the clay was removed from the receptacle, leaving an Ecoflex mold in the shape of the clay. The clay’s void space was first sprayed with mold release and then filled with a mixture of Ecoflex and dried following the same conditions used in the previous step. d. The resulting Ecoflex earpiece was removed from the mold to use in further experiments. e–f. Sweat mapping using a costume Ecoflex earpiece. (e) With the help of a tweezer, small cavities were made in the resulting Ecoflex earpiece. Next, pieces of filter paper (2 ×4 mm) were modified with an edible blue dye covering a certain area (2 × 1 mm). These pieces were inserted inside the cavities of the earpiece, exposing the area with blue dye to the ear skin. (f) Three participants (n = 3) wore the resulting earpiece to perform 30 minutes of stationary cycling at a fixed level. Before exercise, no dye stain was observed due to the absence of sweat (i). After concluding the 30 minutes of exercise, dye spread across the filter paper was observed, indicating areas of higher sweat secretion(ii).