The only cooling system a dog actually has
A dog's skin produces almost no sweat. The merocrine sweat glands in their paw pads release a small amount of moisture, but not nearly enough to regulate core body temperature. Everything depends on the respiratory tract. When a dog pants, it moves air rapidly across a wet tongue and the moist lining of its mouth and upper airways. That moisture evaporates, pulling heat out of the blood vessels directly beneath the surface. The cooled blood then circulates back through the body. It is a tight, elegant loop, and it has one hard requirement: the surrounding air must be dry enough to accept that evaporated moisture.
