Dogs can't sweat like humans.
The nose serves not only as an olfactory organ but is also elementary for the cooling of the dog. It's the dog's air conditioner.
When inhaled through the nose, moisture evaporates in the so-called wrinkled tissue in the nose, resulting in evaporation cooling. The greater the heat, the faster the dog breathes and begins to pant. The tongue of the dog contributes only slightly to the cooling of the dog, because its surface is too small. If the wrinkled tissue of the nose were spread, it would cover almost the entire surface of the dog.
At high heat the dog pants up to 200-300 per minute and exhales through the nose and snout. An enormous effort for the circulation and organs of the dog!
Dogs with short noses (pug, bulldog, etc.) now quickly develop heat stress, as the short nose is not sufficient to provide the required cooling. Brachycephal respiratory distress syndrome (BAS) is intensified by the reduced cooling effect of the nose, since cooling by panting is not sufficient.
But also with older or very active dogs the circulation of the dog quickly reaches its limits.