Your dog may bite when he's playing, defending himself or sorting out his place in the pack. As natural as it might be with other dogs, though, it is not acceptable for a dog to bite his owner, even if the dog thinks he has a good reason.
Dominance or aggression can cause a dog to bite his owner if the dog believes he is, or should be, in charge of the family "pack." This type of biting often happens when an owner touches the dog or his food while he's eating, or tries to take away a treat or toy. The dog believes he is the leader and his human companion does not have the right to interfere with him, so he bites to get his owner to be submissive.
Fear or Surprise
Dogs who are otherwise submissive or timid can bite their owners out of fear or surprise. A new, scary or chaotic situation can trigger a dog's fight-or-flight response, and if he can't flee, he will bite. Often the situation does not appear scary to the owner, and the dog bites quickly and then retreats. A bite might also appear accidental if the dog is startled or surprised by his owner's touch or presence. In both cases the dog needs training and exposure to new situations to help him overcome his shyness and fears. Basic obedience training can be helpful to teach the dog to trust his owner.
Illness or Injury
Even the most easygoing, laid-back dog can bite his owner if he's in pain. His instinctive reaction is to protect the injured or painful area and stop anything that's causing him pain. Broken bones, lacerations and ear infections can all cause an otherwise affectionate dog to bite. If your dog is showing any signs of pain or illness, have him examined by a veterinarian. He should also have a complete checkup if he has bitten you for no apparent reason.
Herding or Prey Drive
Breeds created to hunt or work often have instinctive drives that can lead to biting. Herding dogs, for example, often nip at the feet of the cattle or sheep under their supervision to make them move. When a herding dog sees his owner running or moving in a way that reminds him of livestock, he may bite at his owner's ankles or feet. Dogs bred for chasing prey or that have a high prey drive, like German shepherds, may display the same type of biting behavior. This type of dog needs to be taught that it is not acceptable to herd, chase or bite his owner or any other human, no matter what his instincts tell him.