Verified by 
When a human being's body temperature builds up, either because he is in a hot environment or because he has been exercising or working a great deal, he begins to perspire. When people sweat, it is fairly obvious. Everybody perspires, although some do more so than others. For some human beings their sweat is only visible under their arms and on their brows, while other people seem to sweat almost everywhere.
Sweating is one of the ways that our body regulates its temperature. In humans, our sweat glands are distributed over most of our body's surface. When our internal temperature rises to an unhealthy level, the sweat provides a slick of moisture over the skin, which then begins to evaporate. As a fluid evaporates it cools, and in that way the sweat helps to lower our body temperature by effectively wrapping us in a thin cool layer.
A dog's skin is quite different, which is why you have never seen a dog with sweaty underarms. Most of the dog's sweat glands are located around its foot pads. That is why, when a dog is overheated, you will sometimes see a trail of wet footprints that he has left behind as he walked across the floor.
Rather than relying upon sweat, the principal mechanism that a dog uses to cool himself involves panting with his mouth open. This allows the moisture on his tongue to evaporate, and the heavy breathing also allows the moist lining of their lungs to serve as a surface from which moisture can evaporate. In this way the dog can manage a significant cooling of his body temperature.
Another mechanism that dogs use to try to cool off in involves dilating or expanding blood vessels in their face and ears. If it is not too hot outside, this helps to cool the dog's blood by causing it to flow closer to the surface of the skin. This mechanism works best if the overheating is due to exercise, rather than a high outside temperature.
You might guess that another reason why dogs might not deal well with heat is because they are covered in fur, which could make their bodies quite hot in the summer. This is only partially the case since fur is actually an insulator that serves as a barrier between the outside environment and the dog's interior. It acts much like the vacuum barrier in a thermos. Thus in the winter the fur preserves the body heat and serves as a barrier to keep the cold out. In the summer it is a barrier to the outside heat. Unfortunately, in a continuously hot environment, once there is a temperature build up in the body, the fur then serves as an impediment to cooling since the heat then has a hard time dissipating through it.
On a hot day, especially if the dog is very active, he can overheat, a condition known as hyperthermia. This can eventually lead to heat stroke. A dog that is overheated will seem sluggish and perhaps confused. If you look at his gums and tongue they may appear bright red, and he will probably be panting very hard. If left unattended to, the dog may collapse, have a seizure, or even go into a coma.
A simple trick that many dog owners use to help keep their pets cool on a hot day, involves using a spray bottle or mister, such as those used on plants. Simply fill it with water and periodically spray your dog's body with it. In effect, you have created a condition where there is a slick of moisture covering your dog, and it will evaporate and have the same cooling effect as if your dog had sweat glands all over his body.
Stanley Coren is the author of many books including: Born to Bark, The Modern Dog, Why Do Dogs Have Wet Noses? The Pawprints of History, How Dogs Think, How To Speak Dog, Why We Love the Dogs We Do, What Do Dogs Know? The Intelligence of Dogs, Why Does My Dog Act That Way? Understanding Dogs for Dummies, Sleep Thieves, The Left-hander Syndrome
Copyright SC Psychological Enterprises Ltd. May not be reprinted or reposted without permission.
