Every hair in the dog coat grows from a hair follicle, which has a cycle of growing, then dying and being replaced by another follicle. When the follicle dies, the hair is shed (moults). The length of time of the growing and shedding cycle varies by breed, age, and by whether the dog is an inside or outside dog.
Many dogs shed their undercoat each spring and regrow it again as colder weather comes in; this is also referred to as blowing the coat. Many domesticated breeds shed their coat twice a year. In some climates, the topcoat and undercoat might shed continuously in greater and smaller quantities all year.
Coat textures vary tremendously. Densely furred breeds such as most sled dogs and Spitz types can have up to 600 hairs per inch, while fine-haired breeds such as the Yorkshire Terrier can have as few as 100, and the "hairless" breeds such as the Mexican Hairless and the Peruvian Inca Orchid have none on parts of their bodies.
Texture, like colour and pattern, might be called by different terms for different breeds, even when referring to the same quality of coat. Some terms used to describe dog coat texture are smooth, rough, curly, straight, broken, and silky.
The texture of the coat often depends on the distribution and the length of the two parts of a dog's coat, its thick, warm undercoat (or down) and its rougher, somewhat weather-resistant outer coat (topcoat, also referred to as guard hairs). Breeds with soft coats often have more or longer undercoat hairs than guard hairs; rough-textured coats often have more or longer guard hairs.
What follows is a short description of the various coats and what they mean:
Double Coated:
Means having both a soft undercoat and a coarser topcoat. Some breeds with this type are Poms, Huskys, Samoyeds, Collies, Shelties and Akitas. The undercoat of a double coated breed can become very matted very easily. These are the heaviest shedders.
Undercoat:
The undercoat lies closest to the dog's skin and grows in clusters from a single follicle. The undercoat has a soft, downy appearance and works to protect the skin from cold weather.
Outercoat:
This is composed of long, stiff guard hairs that protect the undercoat.
Single-coated:
Lacking an undercoat. Single coated dogs include poodle, Maltese, Yorkshire Terrier,
Soft Coated Wheaton Terrier, Kerry Blue Terriers, Portuguese Water Dog. Many of these dogs do not shed much if at all.
Smooth-coated:
Smooth to the eye and touch. This would refer to dogs such as beagles, labrador retrievers, greyhounds, etc. Smooth coated dogs often shed quite a lot.
Long-haired:
A "long haired" dog typically has hair longer than an inch or so.
Short-haired:
Dogs referred to as short-haired have hair around an inch long or shorter.
Wire-haired:
Also called broken-coated. The harsh outer guard hairs are prominent, providing excellent weather protection for hunting dogs such as the Border Terrier or Wirehaired Pointing Griffon. Shedding is minimal for most wire-haired dogs.
