There are a few reasons why people sweat when hiking. The most common reason is that the body is trying to cool itself down. When you’re sweating, your body releases water and other fluids in order to dissipate heat. Additionally, when you’re hiking uphill or climbing, your muscles are working harder than they do when you’re walking or running and they produce more heat. Finally, the air temperature can be hotter than the surface temperature on trails which can cause your skin to perspire more easily.