Contrary to popular belief, hair does not grow continually but instead grows in cycles. Hair is primarily composed protein. If you were to measure the amount of hair produced daily on a single dog, you would find that collectively all the hairs would produce 60-70 feet of growth in a single day. It has been rumored that heat affects the shedding process, which is true to an extent, but the amount of sunlight the dog is exposed to dominates the shedding process. Illness, stress, disease, pregnancy, or malnutrition may cause the hair to enter the shedding process early and may cause excessive hair loss. In severe cases, there may be obvious hair loss. Hair moves through three different stages, the Anagen, the Catagen and the Telogen stages.
The Anagen Stage
In the Anagen stage, the hair follicle is growing and actively producing hair.
A single hair can be in this stage for a few days up to 25 years. The length of the Anagen stage is genetically determined. Short hair has a short Anagen stage, and long hair, therefore, is in the Anagen stage for an extended period. That is why dogs such as German Shepherds and Collies have short hair on their face and legs and have longer hair on their bodies. The amount of time that their hair is in the Anagen stage has been genetically determined.
The Catagen Stage
An intermediate interval where the bulb of the hair shaft shrinks while the base of the hair follicle becomes bulky and begins working its way up to the epidermis (the outer layer of the skin).
The Telogen Stage
This is a stage of inactivity, a resting stage for the hair follicle. This is the stage where the old hair is shed and replaced by a new, Anagen
Breeds and Shedding
In many breeds, such as Dalmatians or Doberman Pincers, it is not necessary to clip the hair. The hair only grows to a certain length and then falls out. Many breeds have a seasonal shedding period, often in the spring or fall, when extensive amounts of hair are shed.
There are several breeds of dogs that are said to be “non-shedding” such as Poodles, Bichons, and many terriers. The fact is that they do shed but to a lesser degree than other breeds. The hair follicle of these breeds may be in the Anagen stage for several years. Therefore, the hair will grow very long unless it is clipped. Most of the non-shedding dogs have a very thick coat of curly hair, and the shedding hairs (hair in the Telogen stage) become entangled in the rest of the dogs’ coat. When you brush a non-shedding dog, you will find that the brush is full of hair, all in the Telogen stage. The non-shedding breeds must be kept on a regular grooming schedule or the Telogen hairs will form into large mats, resembling a fabric called felt. A matted dog is more difficult to clip. Also, the mats can cause the skin to trap dirt and can make the animal more prone to skin infections.