A U.S. research team has found behavioral or painful medical problems, rather than breed can prompt dogs to bite children. The study, published in Injury Prevention, also showed two-thirds of dogs, that bit children, had never bitten a child before.

Researchers at the University of Pennsylvania looked at 111 cases involving 103 dogs that bit children.

According to the study in the journal Injury Prevention, "Guarding of resources and territory" were the most common triggers for aggression by these dogs. Food guarding was the most common cause of bites involving children familiar to the dog.

Territorial guarding was the most likely cause in cases involving unfamiliar children, the report said.

The results also found that three-quarters of the dogs exhibited anxiety when left by their owners or exposed to loud noises. Half of the dogs had medical conditions, mostly affecting bones or skin.

Also, a report by the Centers for Disease Control and Prevention's (CDC) emergency room show children under the age of 14 account for 42 percent of U.S. dog-bite admissions.

Since young children often can be noisy and move unpredictably, both of which frighten an already anxious dog, they are more prone to be bitten by a dog. In cases involving older children, the bite was more likely the result of a dog's territorial behavior, the authors said.