Your Dog's Fur
Skin is protected by a layer of hair, or fur, referred to as the coat. Dogs come in a variety of coat types. There's the long, silky coat of the Afghan hound or papillon; the short, thick coat of the pointer or Great Dane; the hard, dense, wiry coat of the giant schnauzer; the curly or wavy coat of the Portuguese water dog or American water spaniel; the straight, coarse, medium-length coat of the rottweiler; the profuse double coat of the Samoyed or chow chow; the woolly corded coat of the puli; the distinctive lamblike coat of the Bedlington terrier, with its crisp mixture of hard and soft hair; the smooth, flat, hard coat of the smooth fox terrier; the short, smooth, fine coat of the Boston terrier; and the suede-like smooth body of the Chinese crested, adorned with a plumy tail, furry feet, and the crest on the head. The reason there are so many coat types is because different breeds produce different sizes and numbers of primary and secondary hairs.
No matter how different the various types may appear, all hair is produced by hair follicles, living cells that lie beneath the skin. Formed by proteins, hair originates in a part of the follicle called the hair bulb and passes through the follicular sheath to emerge at the surface of the skin. Each individual hair is called a hair shaft. Although follicles are living cells, hair itself is a dead structure.
Every hair shaft has three layers. The outside of the hair is called the cuticle. Inside the cuticle is the cortex. The inner layer is called the medulla. A structure known as the hair root anchors the shaft to the skin.
Each follicle produces bundles of seven to fifteen hairs. These bundles usually consist of one long, stiff primary, or guard, hair and a number of finer secondary hairs, which are also called underhairs.
Different breeds of dogs have different numbers of hairs. The density of hairs per square inch varies from breed to breed. The dogs that we tend to think of as heavy shedders have either long hair or a dense undercoat. Don't be fooled if your dog doesn't seem to shed. All dogs shed hair; it's just more apparent with longhaired dogs or dogs with thick undercoats. Paradoxically, dogs with short hair shed the most.
The Importance of Hair
For a dog, hair isn't just decoration. Hair has a protective function, keeping the skin safe from physical traumas such as cuts and scrapes, sun damage — yes, dogs can get sunburned! — and chemical irritants with which the dog might come in contact. It also helps insulate the dog from temperature extremes. All in all, the coat has a tough job. Dogs spend a lot of time scratching at and lying on their coats. In addition, all that abuse from sun, air pollutants, and scratching takes a toll on fur, so periodically the body sheds the old and damaged hairs and replaces them with new hairs.
Ever wonder why poodles and bichon frises don't seem to shed?
The secret to their nonshedding reputation is that their hair has a longer growth cycle than that of other breeds, so hair isn't replenished as often. If you're a lousy housekeeper, you can go about a month without vacuuming before you start to see poodle dust bunnies.
Hair Growth Cycle
The life cycle of hair is one of growth, rest, loss, and replacement — a process that's called shedding, or blowing coat. Hairs in different parts of the body grow to genetically determined lengths. This growth period is known as the anagen phase of hair growth. Once hair reaches its predetermined length, it rests, a period known as the telogen phase. After this rest period, new hair begins forming. As these new hairs rise through the follicular sheath, they push out the old hair, which is when it lands on your clothes, floor, and furniture.
You may notice that hair seems to grow and shed at certain times of the year. That's because hair growth and loss is affected by the number of hours of daylight to which it's exposed. Hair grows thick in the fall, in preparation for cold winter months. As the days grow warmer and longer, all that excess hair falls out, to be replaced with a cooler summer coat. If your dog spends most of his time indoors, his coat is less subject to these seasonal cycles, and he will probably shed small amounts year-round.
Hormones also affect shedding. Females that aren't spayed usually shed twice a year, at the same time they're in heat. Spayed females, on the other hand, usually develop a very full coat because they don't have that periodic surge of hormones. They're more likely to shed year-round than seasonally.
The first time you see the shed of an Alaskan malamute, chow chow, or other breed with a heavy double coat, you may think the dog has an awful skin disease. The fur comes out in big clumps, and the coat can look pretty patchy and ratty. Don't worry! Unless the dog has actual bald spots, this is normal.
On the other hand, hormonal diseases such as hypothyroidism, certain hereditary abnormalities, and even stress can cause dogs to shed abnormally. Dogs with hypothyroidism often develop symmetrical hair loss on the body. For instance, the dog might lose hair on both of its rear legs. The coat doesn't look healthy, either. It becomes thin or sparse and falls out easily. Dogs whose bodies produce too much cortisone (Cushing's disease) also tend to have this symmetrical hair loss. When stress is a factor, hair loss often occurs in specific areas, such as the rear end, where hair typically grows quickly.