There are many kinds of aggressive behavior among dogs. When any dog snarls or growls and bares its teeth regardless of breed, size, age and sex, this conduct should be taken seriously. Such behavior can mean a variety of things from a medical condition that is causing the dog pain and needing medical attention to a threat that can mean eventual harm to a person or other animal.
Aggressive temperaments that appear in puppyhood should be dealt with early on or suffer more serious consequences later on. Many types of aggressive behavior can be controlled or modified, but not "cured". The help of an experienced professional who understands the behavior is recommended. So, if you cannot understand and handle your dog’s aggressive behavior, do not make it as a family pet especially when young children are around.
Dog aggression is a problem. In the US and other countries, insurance companies are refusing to insure homeowners and renters with dogs. The fact remains that hundreds of thousands of people are seeking medical attention because of dog attacks and deaths definitely occur due to aggressive canines.
--- I received the tragic photos above from an email.