Dogs do sweat. Sweating is a physiological response to heat where sweat glands secrete salty water. When the water evaporates, it takes energy with it, cooling down the organism in the process. Although dogs don't sweat profusely and visibly the way humans do, they definitely have sweat glands that secrete sweat in response to heat. The problem is that most dogs are covered with a thick coat of fur, so sweat secreted where there is fur would get trapped in the fur, fail to evaporate, and therefore fail to cool the dog down much. As a result, it is far more efficient for dogs to have sweat glands where there is little fur. For this reason, most of a dog's sweat glands are located on the pads of its feet and on its nose. On a hot day you may notice a dog leaving behind a trail of wet footprints as it walks across a smooth, dry surface. That's dog sweat.