On hot days we often see dogs sitting with their mouths open and their tongues hanging out. If you listen closely, you can hear them taking very short, quick breaths of air. When dogs do that, they are panting.
To understand why dogs pant, we need to know this important scientific fact: When dry air blows across something that is wet, the air cools off the thing that is wet. If you run some water that is neither hot nor cold onto one hand, then blow on both hands, the wet hand should feel a lot cooler than the dry one.
When we humans are hot, we sweat. Perspiration is wet, so when a breeze comes along, we cool off. Dogs and cats don’t sweat because they don’t have sweat glands. But when a dog pants, it uses this air-over-wetness principle. Its panting keeps air moving across the surfaces of its wet tongue, mouth, and lungs and cools them. So, when a dog pants, it is keeping cool!
Cats keep cool in hot weather by licking themselves with their wet tongue. When their fur gets wet and dry air moves around them, they cool off.
So the next hot day when you see a dog’s sides heaving or a cat working hard at “cleaning” its fur, remember that it may just be keeping cool.