How dogs sweat

Dogs do not sweat in the same way people do. When our body temperature increases, either due to an increased ambient temperature or higher activity levels, our bodies start to sweat in order to regulate our body temperature. When our core temperature exceeds acceptable limits, our bodies try to lower it in various ways. They activate the sweat glands that exert a certain amount of sweat on the surface of the skin, which then evaporates and cools it, thereby decreasing the temperature. As sweat glands are distributed over most of the human body, sweat is noticeable nearly everywhere. A dog’s skin has a somewhat different structure, with most of the sweat glands located on the limbs, around the paw pads. Therefore, when your pet sweats, i.e. tries to reduce its increased temperature, you may notice wet paw prints on your wood or tile flooring. 

Releasing heat

Dogs mostly use panting as a way of releasing heat, which leaves their mouths open. This ensures that moisture evaporates from their tongues, while rapid breathing leads to air circulating through the lungs and then evaporating as well, radiating heat and cooling down their bodies in the process. Blood vessels also play a role in reaching an ideal body temperature and preventing overheating. Vessels located just under the skin, especially around the face and ears, dilate (their lumen increases) to slow down blood flow and allow the blood to cool. The dog’s coat also plays a part in maintaining optimum body temperature – it prevents hypothermia in cold weather and hyperthermia in hot weather. 
Although dogs have an extremely efficient mechanism of maintaining optimum body temperature, we need to help them and prevent potential overheating, which can lead to health issues. So, on hot and humid days, you should change their water several times a day, but make sure it is not too cold, so as to avoid inflammations of the throat, tonsils, etc. 
The dog should also have access to a spot away from the sun (a house or a place in the shade), and you should limit its playtime during the hottest hours of the day.