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Only mammals have sweat glands. Mammals are warmblooded, which means they regulate their own body temperature. Sweat glands produce moisture that evaporates on the skin to cool the body when it is overheated. Coldblooded animals rely on the external environment to regulate their body temperature, so they do not have sweat glands. Reptiles, amphibians and fish lack sweat glands. Not all mammals rely exclusively on sweat glands to cool them down. Dogs, for example, also pant. A few mammals have no sweat glands.
The hippopotamus does not have true sweat glands. This animal spends most of its time in water, which regulates its body. A hippo’s skin must be wet most of the time, or the hippo will get dehydrated. When the hippo is out of the water, a thick red liquid that looks like blood oozes from its pores. This liquid protects the hippo’s skin from the elements and keeps it moist to prevent dehydration.
The rhinoceros also does not have sweat glands. Rhinos frequently roll in mud that mud covers their skin and cools them, as well as protecting them from insects and parasites. The rhinoceros is the second-largest land mammal in the world. An adult male rhino may weigh more than 2 tons. Rhinos are generally docile herbivores.
Whales, Dolphins and Porpoises
Whales, dolphins and porpoises are marine mammals of the order Cetacea. Because they live in water all the time, they do not have sweat glands. Rather, they depend on the surrounding water to regulate their body temperature. There are cetaceans in every ocean as well as some freshwater lakes and rivers.
Pigs do not have sweat glands. To keep cool they roll in the mud as rhinos do. A covering of mud protects the pig from sun damage and insect bites. The domesticated farm pig might be the best-known, but swine species vary widely throughout the world. All pigs roll in mud and use their snouts to root for food. Some species also have hair or tusks.
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