The purpose of this study was to determine the effect of stratum corneum (SC) hydration by distilled water on SC ion content and sweat ion concentrations as measured by occlusive sweat patch. 10 men and 10 women completed approximately 40 minutes of moderate exercise in the heat. Select skin sites were hydrated before sweating by adhering cylinders of distilled water to forearm skin. SC samples were taken before and after exercise using the tape stripping (TS) method and sweat samples were taken with homemade filter paper sweat patches with a tegaderm backing. An increase in SC hydration was verified by a reduction in SC potassium concentration (p<0.05). SC hydration caused a significant decrease in sweat potassium (K+), calcium (Ca++), and lactate (Lac-) concentration: K+ =8.14 ± 0.46 to 6.56 ± 0.46, Ca++ = 0.86 ± 0.17 to 0.67 ± 0.18, Lac- = 11.64 ± 1.36 to 8.82 ± 1.11, euhydrated to hyperhydrated respectively(p<0.05). SC sodium (Na+) and K+ concentration increased after sweating without a sweat patch (p<0.05). Our data do not dispute the idea that electrolytes can be leached from the SC by distilled water or sweat trapped within an occlusive dressing. However, our data indicate that during normal sweating the SC "dehydrates" resulting in an increase in the electrolyte concentration. As such, we propose that the occlusive dressing does trap sweat on the skin but the important end result is that it prevents water movement out of the SC and thereby producing a more concentrated sweat.