Do you know what makes a mammal a mammal? One of the things is hair. Hair is closely related to fingernails, snake scales, and feathers because all are made of keratin. Hair does a number of things for mammals. It protects the skin from sun and scrapes, sends sensory messages to the brain, and provides insulation from cold and heat. The shape of hair also gives a mammal a unique look with its different shapes; round hairs tend to be straight; oval or flattened hairs are curly.

Hair Types

Not all hair is the same. If you have a dog or cat at home, take a close look and see if you can find these different types of hair.

  • Guard hairs - are the ones most obvious to see. They are protective or "guard" outer hairs of a mammal's coat. They are typically firm and glossy. Some hairs grow to a particular length and stop; others grow continually, like human head hair, horse manes, and quills of a porcupine.
  • Vibrissae or whiskers - stiff hairs, usually long, with many nerves at their base. They are extremely sensitive to touch. These hairs give the mammal clues about its immediate surroundings. Facial whiskers are most familiar, but they also appear in other places on a mammal's body such as on the ankles of a squirrel or the rump of some crevice-roosting bats.
  • Underhairs - these hairs are short, curly, wooly, and are called down or fuzz. Insulation is the most important role of these hairs. Special glands secrete oil to waterproof the skin and hair. Deer have hollow hairs in winter which provides more warmth.

Coats of Color

Pigments in the inner layers of hair filter harmful ultraviolet radiation just like sunscreen, and may help regulate body temperature. Dark hairs absorb heat, warming an animal, while light colors reflect sun, keeping an animal cooler.

Hair color helps camouflage animals from predators or prey by matching the environment they live in. Some northern animals, like the snowshoe hare, alternate between brown and white as the seasons change in order to be concealed against their surroundings. Patterns in the hair or fur also help protect mammals. Think of a fawn's spots which helps hide it from predators. Color can also provide a warning, like a skunk's stripe which announces the presence of an especially good and stinky defense system. The under-color of a white-tailed deer's tail serves as a flag to warn other deer of danger. Hair can also communicate social information about a mammal's state of mind, such as the hair standing up on the back of a wolf or dog which indicates that it feels threatened or is ready to attack. And, in the case of the porcupine and its quills, hair can provide protection from predators.