The dog’s coat – hair growth and shedding in dogs

Skin disease is a common problem in dogs. The condition of the skin can also tell you a great deal about your dog’s general health. A dog’s skin is thinner and more sensitive to injury than human skin. It is easily damaged by rough handling with the wrong type of grooming equipment, and once the surface of the skin is broken and disturbed by trauma or some other disorder, the condition tends to spread rather easily and become a major problem.

The outer layer of skin is the epidermis, a scaly layer that varies in thickness over different parts of the body. For example, it is thick and tough over the nose and foot pads, and thin and most susceptible to injury in the creases of the groin and armpits.

The layer beneath the epidermis is the dermis. The dermis gives rise to the skin appendages: hair follicles, sebaceous glands, nails, and sweat glands. Sweat glands are found only in the foot pads of dogs.

Hair follicles produce three types of hair. Primary hair is exemplified by the long guard hair that makes up the top coat. Generally, each guard hair grows from its own follicle, but in some breeds more than one hair may grow from a single follicle. Muscles connected to the root of each guard hair enable the hair to stand erect, as happens when a dog raises her hackles.

Within each guard hair follicle is a cluster of accessory hair that composes the undercoat. The function of the undercoat is to provide warmth and protection. Whiskers and eyelashes make up a third type of hair, which is modified to serve the sense of touch.

Sebaceous glands are located in the dermis, and are linked to the hair follicles. Sebaceous glands secrete an oily substance called sebum, which collects in the hair follicles and coats each strand of hair. This adds shine and, more important, enables the hair to shed water. Water-going breeds depend upon sebum to waterproof their coats. Sebum is also responsible for the characteristic doggy odor apparent in some dogs with oily coats.

The color of a dog’s skin can vary from pink to light brown, or it may be dark with patches of black. The dark pigment in the skin is called melanin. It is produced by cells in the dermis called melanocytes.

The Dog’s Coat:

Cross-Section of the Skin

The quality of a dog’s coat is controlled by a number of factors, including hormone concentrations, nutrition, general health, parasite infestations, genetics, and the frequency of grooming and bathing. Dogs who live outdoors in cold weather grow a heavy coat for insulation and protection.

Hormonal disorders such as hypothyroidism, hyperestrogenism, and Cushing’s syndrome slow or suppress hair growth, making the coat appear thin or sparse. A protein deficiency caused by parasites, poor diet, or ill health may cause the coat to be dull, dry, brittle, and thin.

If your dog’s coat is below par, have her checked by your veterinarian. Poor coat quality is often an indication of a systemic disease.

Hair Growth and Shedding:

Dog hair grows in cycles. Each follicle has a period of rapid growth (the anagen phase), followed by slower growth and then a resting phase (the catagen phase). During the resting phase, mature hair remains in the follicles and eventually detaches at the base. When the dog sheds her coat (the telogen phase), a young hair pushes out the old hair and the cycle begins anew. The average dog takes about four months to grow a coat, but there are individual and breed variations. The Afghan Hound, for example, grows her coat in about 18 months.

There are “hairless” dog breeds, such as the Chinese Crested (which has hair on the head, tail, and legs) and the Xoloitzcuintal (which is normally hairless except for a single tuft on the head and some long hairs on the tail). Both of these breeds have coated versions as well. The hairless condition in these dogs is due to a genetic mutation, not a health problem.

Most dogs shed or “blow” their coat at least once a year. Dams often blow their coat six to eight weeks after delivering puppies. Major shedding may follow a bitch’s heat cycle as well, due to the hormonal swings.

Many people assume that temperature changes govern when a dog sheds her coat. In fact, the seasonal length of daylight exerts the major influence. Longer periods of daylight in spring activate a shedding process that lasts four to six weeks. In fall, as the daylight hours grow shorter, many dogs may again shed their coat. Sensitivity to ambient light is most pronounced in dogs who live outdoors. Dogs who live primarily indoors are exposed to artificial light and a rather fixed photoperiod. These dogs may shed and grow new coats all year long.

Some breeds, such as Poodles, Bedlington Terriers, and Kerry Blue Terriers, have what is called a nonshedding curly coat. These breeds do not shed loose hair into your house. Instead, their loose hair tends to collect into mats that remain on the body. Dogs with corded coats, such as the Puli and Komondor, have similar coats, but their hair works itself into cords.

Some dogs have a double coat comprised of long, coarse outer guard hairs and a soft, fine, wooly undercoat. When a dog with a double coat begins to shed, the appearance of the coat can be quite alarming. The undercoat is shed in a mosaic or patchy fashion, giving the dog a moth-eaten appearance that may suggest a skin disease.

When shedding begins, remove as much of the irritating dead hair as possible by daily brushing. In breeds with a thick double coat, a bath will loosen the dead hair and make it easier to remove. Always brush out a dog before bathing to help prevent the formation of mats.