Along with being warm-blooded and producing milk, hair is one of the determining characteristics of being a mammal.  Hair is an outgrowth of protein, found only on mammals. The primary growth of hair fiber is keratin;  giving them the same chemical make-up as skin, feathers, and nails.  Hair projects from the epidermis, though it grows from hair follicles deep in the dermis. The term fur refers to the body hair of non-human mammals.

There are some differences between hair and fur.  Fur tends to grow in a synchronized pattern.  Hair tends to grow independently.    Human follicles each give rise to a single hair and do nothing to provide temperature regulation for the body except in the area which it grows.

Animals that depend on fur coats for temperature regulation often have several or many hairs per follicle.  Fur provides excellent insulation not only from heat and cold, but also a fair amount of protection from rain as well.  Oftentimes, hair and fur serves as protection against injury. An excellent example of this is the thick coat of fur around a lion‘s neck.  His mane will make it very difficult for his enemies to wound him, especially as big cats and other carnivores often go for the throat when hunting. In addition to this, hair and fur can further serve to carry a scent that can vary in purpose from species to species. Although much of the hair that grows on human bodies seems unnecessary, most believe that its growth has greatly reduced, along with our reduced need.

Most people are also convinced hair and fur are different because fur tends to grow to a set length. The truth is, in every mammal, hair and fur growth are determined by genetic make-up. So a shorthaired cat doesn’t suddenly become a longhaired cat if it doesn’t get a haircut. 

Opossum fur is layered; having dense “ground hair” or “underfur” which is white with grayish tips.  The top layer consists of longer, often coarser, straight shafts of hair that stick out through the underfur called “guard hair”.  Guard hairs are dark gray or black and are usually the visible layer for most mammals and contain most of the pigmentation.   From a distance opossums appear grayish in color.  Some individuals may have underfur tipped in brown, and these animals will have a brownish cast rather than gray.

Opossum hair example

Fur and hair grows in cycles.  If your opossum is shaved for surgery or has gross hair loss from some other cause, you probably won’t see hair regrowth until the spring.  An opossum needs its fur for protection from the weather.  Please consider the condition of their fur for winter releases, especially if it’s a female who will breed and need to carry babies on her back by April.  Babies scrambling to hang onto a mother’s back will fall off if Mom’s hair is depleted and not had a chance to grow back.

Remember, an opossum’s fur can protect it from both heat and cold.  During your initially exam of the opossum, be sure to take in the condition of its fur.  Skin and fur can reveal other conditions.  Take into account the condition of the fur for the time of year you will need to release the opossum.

** Editor’s note:  I have often wondered if opossum’s hair regrowth after trauma differs from climate to climate.  I would welcome your observations.