Dogs often bite when humans intervene while they are playing or fighting with another dog. Guarding resources, such as toys or food, can also lead a dog to bite.
Dogs often bite out of fear or pain. Most dogs try to retreat from things they find frightening, but people sometimes do not allow them to do this. That can cause the dog to bite in an effort to protect itself. Injured or sick dogs might bite people in a misguided effort to protect themselves, even if the people are trying to help them.
Dogs more frequently bite children since children may not notice when dogs become uncomfortable and continue to provoke or frighten them. Children may also accidentally hurt dogs by jumping on them or pulling their ears or tails.
Dogs often nip or bite during play. Puppies most often do this because they have little bite inhibition. If humans and other dogs never teach a puppy not to bite, it may continue to bite as it grows up. Overexcited dogs may also bite out of frustration.
Although some breeds are commonly considered more aggressive than others, all dogs can bite in the right situation. Good training and socialization can result in less biting, and adults should provide supervision whenever children and dogs interact.