Why on earth does my dog scoot his rear on the carpet?

Allergies
Dogs, like people, may develop allergies to various pollens, molds, dusts and other substances in their environment.  Less commonly, they may develop an allergy to varying items in their diet, with the most common being a protein such as beef, pork or chicken.  The allergic response produced from an encounter with one of these items, can cause inflammation in the perianal (area surrounding the anus) region.  To scratch the itch, your pet may scoot their rear.

Parasites
Historically speaking, most pet owners have been led to believe that scooting is caused by parasites such as tapeworms.  While this may be a cause, it is not always the reason.  Dogs with fleas and/or a flea allergy may also feel the urge to scratch their itch on your floor.

Full or Impacted Anal sacs
Dogs (and cats) have two sacs just on the inside of their anus containing a gland that produces a foul smelling, sometimes thickened secretion.  This secretion is used for scent marking, sometimes released in fear and also the reason why dogs greet each other from the back!  Ideally, your pet should release this secretion when he has a bowel movement.  However, in some dogs, this material becomes extremely thickened or the anal sac itself becomes inflamed rendering your dog unable to release the secretion.  From discomfort or a sense of fullness, your dog may scoot his rear end on the carpet in efforts to express this material.  This may lead to infection (abscess) and rupture causing extreme pain for your dog.  Some dogs may need to see their veterinarian regularly to have their anal sacs emptied.

So the next time you see Scruffy scooting on the carpet, schedule an appointment with your veterinarian to help sort out the cause!