Hospitals treat hundreds of thousands of dog bite injuries every year—most of them to children—but detailed information about the incidents themselves are hard to come by.

A recent study conducted by the Penn’s Schools of Medicine and Veterinary Medicine, as well as the Children’s Hospital of Philadelphia (CHOP), has produced the most thorough analysis of children’s behavior and dog bites to date.

The survey-based study, led by Ilana Reisner, a behavior researcher at Penn Vet, drew upon CHOP patients under the age of 18 who had come to the emergency department to be treated for a dog bite. Reisner and her colleagues asked the children and their parents detailed questions about their history with the dog, the setting where the bite occurred, and most important, what the child was doing at the time that might have provoked the bite.

The data suggested there are two main categories of bites: those that occurred between familiar dogs and young children in household settings, and those between unfamiliar dogs that had gotten away from their owners and older children. The former group was more prevalent than the latter, and was particularly noteworthy in that such bites often occurred when children were interacting with a docile dog, which often had no history of aggression, while family members were nearby.

Bites in the second group generally happened to children over age 7 who were attacked by a loose dog while they were engaged in some activity, such as playing or riding a bike.

Researchers say the two categories necessitate two different kinds of prevention. “On one side there is community prevention and dog control, and the other side would be having better information about these really subtle provocations that familiar dogs can be reactive to,” says Reisner. “It’s always been a high risk for families who don’t realize that simply petting a dog, even one that’s never bitten before, can result in a bite. There’s always a first time.”

Reisner urges some basic cautions when teaching young children how to interact with dogs, such as calling a dog over rather than approaching it.

Reducing the number of loose dog bites would require a community-level response, but that could also start with educating owners about the proper way to restrain their dogs, and increasing awareness in older children regarding when and where such bites tend to occur. Reisner suggests that owners should not completely rely on in-ground electronic fences to avoid bites, nor should they tether dogs because the dogs can still get loose, and often are more aggressive when they do.

“Even though we have a close bond with dogs, we really speak a different language,” says Reisner. “What we consider to be affectionate, dogs can consider to be provocative.”