While it depends how big your dog is, on average, dogs have from 15,000 to 25,000 hairs per square inch of skin.
According to MyGermanShepherd.org, there are at least three types of dog's hair, and thus three types of hair follicle:
Guard hair or Primary hair or Top hair gives the outer coat or top coat. It is thick, long and stiff hair that normally grows at one hair per primary follicle. This primary hair is most abundant on the neck and back of the dog, to protect the skin cells from rain and sunrays.
Secondary hair or Insulating hair or Under hair obviously gives the undercoat. It is thin, short and soft hair that grows at up to 15 hairs per secondary follicle. This hair is similar to the silky soft hair that newborn puppies have (only), and some adult dogs have so little Under hair that they are simply said to have "no undercoat". Long coat German Shepherds are like that. While dogs that appear hairless, like the American Hairless Terrier, actually do have this thin, short and soft Secondary hair. There is no such thing as a bald dog - unless the dog suffers a severe defect (see the prior Periodical Hair Loss in Dogs).
Tactile hair or Sinus hair is the thickest and stiffest hair. It is even thicker than Guard hair, however contrary to the other two hair types it is rooted in a blood filled sinus surrounded by sensory cells which amplifies the motion of the hair and thus increases sensitivity to its movements (makes sense for tactile hair)! Most Tactile hair grows on the head: as whiskers, eyebrows/eyelashes, and chin hair. Tactile hair too sheds, but much slower than the other hair types.
The main functions of hair are:
to prevent foreign objects from reaching the skin (the last barrier of the body!)
for dogs, to regulate body temperature
to provide sensation to stimuli in the environment
for dogs, to serve as signal in social interactions
for dogs, to provide camouflage in the environment
To learn more about German Shepherd Dog Hair Growth, visit MyGermanShepherd.org.
Learn How to Manage German Shepherd Hair at the nest and check out German Shepherd Grooming Tips and Secrets shared by Total German Shepherd.