Most dogs don't ever bite a human. But sometimes even reliable pets bite in certain situations. If you know what may trigger a dog to bite and can avoid that situation, you are less likely to get hurt.
In the past, dogs were bred for protection. They guard and protect their possessions, homes, food and territory. If a dog thinks you are trespassing or threatening to take something from him, he may bite to prevent such action.
Some dogs become overexcited during rough play and bite. Anyone who interacts with your dog should be told not to tease, yell or be physically rough.
One of the most common reasons dogs bite is because they are afraid, not because they are aggressive. Fear biting is more unpredictable because you may not know that your dog is afraid until he reacts.
Sick, injured or elderly dogs may be more irritable or afraid than a healthy dog. These conditions may cause them to bite unexpectedly, particularly if there is no history of biting.
As puppies, dogs should be socialized to humans and other animals. Dogs that are poorly socialized are more frightened of new things. They may also be more aggressive than well socialized dogs.