Dogs have no sweat glands. They don't release excess water and salts from circulation in the body through them as many mammals are won't to do with the exception of hogs and hippos. They sweat through their mouths and thats why they can be seen panting in hot weather. They open their mouth in an effort to cool themselves since this is one of the primary functions of sweat. Thats why in hot weather, I take my dogs out for a swim and I can see the excitement on their faces. They really relish the activity. Lack of sweat glands should be one of the reasons we should groom dogs to remove grime from their coats and afford them a chance to relax.
Yeah, when we had our first dog, the dog breeder told us that dogs don't perspire and they ventilate their body thru their mouth by panting. That's why we always have to be aware of that panting because when they are suffering from extreme heat that panting is their only defense unlike humans who would sweat it out to cool the body. That's why we sometimes see when a big dog is outdoors and the weather is very hot, the dog is wiped by ice to cool its body.
That lack of sweat glands is also one reason why dogs are susceptible to kidney stones because the salt is not evaporated thru the sweat. The best defense for the salt is to give your dog plenty of water regularly. Since we have a sad experience with kidney problem, we monitor our dog's drinking and if a dog doesn't drink after having a meal, we force it to drink the water by the use of a syringe.
I wish my dog knew how to swim haha. She's too little and too scared for it.
I pay a lot of attention to my dog's breathing, and if she's hot. Every time I take her for a walk, I press my palms into the floor for 5 seconds. If I can't endure it, it's too hot for her little paws too. People forget that dogs tend to feel hotter way easier than we do, not only because of the sweat glands but also because of their fur. Owners always need to remember when to trim your dog's hair in the summer. Your pet can't cool himself the way you do!