Cats are perhaps most admired for the sleek coats which are also the primary means for identification of the different breeds. The main purpose of a cat’s coat is to provide a barrier between the cat and its environment, protecting it from injury, heat, cold, wind and rain. For the owner, the appearance of the coat is a good general guide to the cat’s health.
Your cat’s fur may contain up to 200 hairs per square millimetre. Except in a few breeds such as the largely hairless Rexes the coat is made up of three different kinds of hair.
The guard or primary hairs form the coarse outer layer.
These are about twice as numerous on the back and sides than on the chest and abdomen. They are rooted in individual follicles or pits in the skin and through them are connected with the nervous system. The guard hairs thus respond to anger, fear, cold, and the excitement of the chase by standing upright, giving the cat an aggressive, ‘fluffed up’ appearance. They also respond to the flow of air and so form part of the cat’s sensory system.
Interspersed with the guard hairs are more bristly awn hairs which have thickened tips. These grow from their follicles in clusters. Below the guard and awn hairs is the soft down hair which forms an insulating layer for the skin. The erection of the guard hairs in cold weather provides the extra insulation which cats need since, unlike dogs, they have no protective layer of fat.
As with human hair, cat hair is constantly growing, dying and renewing itself. In long-haired cats the moulting process is continuous all year round, but in shorthairs, it is most noticeable in spring when the thick winter coat is shed. This pattern is less obvious with shorthairs which are kept indoors in centrally heated homes.
The hair follicles have a secondary purpose which is essential to feline health. They secrete sebum, an oily substance which spreads along the hairs and gives it its shine. Sebum also contains a natural steroid, cholesterol, which is converted by sunlight to vitamin D. Cats obtain part of their supplies of this essential nutrient from fish oil and animal fats, which are present in commercial cat foods, but the action of sunlight on the skin provides an important additional fat source.
The hair follicles also contain sweat glands.
The main function of these is to produce a scent which is used to mark territory and, in unneutered cats, to make sexual signals. They are most prominent on the chin and ears and at the base of the tail. The cat’s coat prevents it from losing heat effectively by sweating,
The hairs of the coat are rooted in the inner layer, the dermis. The outer layer, the epidermis is mainly protective. The cells which make up the epidermis are constantly dying and being renewed, the dead cells either dropping away through the coat or being removed during grooming.
On the nose and feet, the epidermis is up to 75 times thicker than on the rest of the body, yet it is extremely sensitive to pressure and temperature. There are sweat glands only on the feet. Unlike a dog, a cat cannot lose heat through its nose pad, any dampness on the skin here is coming from the mucous membranes inside the nose and the only glands that correspond to human sweat glands are on the hairless skin of the paws, which becomes damp in extreme heat or fright.
If a cat makes wet footprints, or pants heavily, it is usually a sign of overheating and action should be taken to cool it down. Most often cats regulate their temperature by the evaporation of saliva in grooming.
On certain parts of the body, the hairs are modified for specific purposes. The most obvious example is the facial whiskers or vibrissae, which are ultra-sensitive and used as a width gauge, to test environmental conditions and, in different positions, to express emotions. There are also sensitive vibrissae on the back of the forelegs which probably help the cat to move silently over unknown territory.