Impacted Anal Glands
Anal glands (anal sacs) are located on both sides of your dog’s anus. The glands produce a strong smelling fluid which is used for territorial marking. Normally, when your dog defecates it puts pressure on the glands, which causes the sacs to secrete onto the feces. If the fluid is not being expressed, the anal glands can get clogged and impacted. Impacted glands can be caused by the dog having soft stools which do not put pressure on the anal glands. The impacted glands cause the dog great discomfort. He will bite and chew at his tail area. Your dog may also scoot his bottom area on the floor. The anal glands can also become infected and abscess.
Allergies
Allergies may be making your dog very itchy and causing him to bite at his tail. Allergies may be caused by fleas, diet or by environmental allergens. The most common food allergens are beef, dairy, corn, wheat and soy. Environmental allergens may include mold/mildew, and tree, grass and weed pollen.
External Parasites
Fleas, ticks and mites can cause great irritation and discomfort. Many dogs and cats are also allergic to the flea’s saliva, which causes the animal to experience severe itching.
Internal Parasites
Tapeworms and roundworms can cause your dog’s anus to be irritated. Tapeworms can be transmitted by a flea bite or by the dog ingesting a flea, which is carrying tapeworm eggs. Roundworms are more common in puppies, and can be transmitted to humans by contact with contaminated stool.
Poor Hygiene
Poor hygiene may be making your dog’s anal area itchy. The hair around the anus can get matted and have fecal matter (fecal mats). This can cause the dog’s skin to get irritated and infected. The fecal mats can also attract flies and cause a maggot infestation on your dog.
Injured Tail
A dog’s tail may be injured causing a fracture, dislocation, abrasion or laceration. Dogs with long tails are more at risk of injuries. An injured tail can cause a lot of pain.
Behavior Issues
Your dog may be biting at his tail due to behavior issues. Dogs that are stressed or anxious may bite, gnaw or lick at their skin. A new pet or person in the household, fireworks, or a household move can cause a dog a great deal of stress.