Dogs and cats can sweat only through the pads of their paws!
This is not sufficient to cool them down in hot weather. Instead, they mainly use panting (dogs) or grooming their fur to regulate their temperature, which causes saliva to evaporate and cool them down.
Important facts about cooling down:
Sweat glands: Dogs and cats have sweat glands on their paw pads, but these are more functional for marking than for cooling.
Panting: Dogs actively cool themselves down through the evaporation of moisture on their tongues and in their airways.
Cat strategy: Cats lick their fur, and the evaporating saliva cools the skin. They also often lie down on cool surfaces.
Danger: As they hardly sweat through their skin, dogs and cats quickly overheat (hyperthermia), which can lead to circulatory failure.
In hot weather, always provide shady places, plenty of water and avoid exertion.
Keeping them trapped in the blazing sun all day long is animal cruelty!