It is often said that a dog is a man's best friend. Often this is true; they are loyal, protective and affectionate. Why, then, do they sometimes lash out and bite? There is no simple answer to this question. Different dogs bite for different reasons, and it may be true that some breeds are simply more hostile than others.
There are a few causes that you can attribute canine aggression to.
Stress and overstimulation
Just like people, dogs can get stressed out or overstimulated and act uncharacteristically as a result. According to the Animal Humane Society, this can take the form of growling, barking, snarling—and yes—biting. It is the dog's owner's responsibility to monitor his or her dog's mood and ensure the situation does not get to this point. Failure to do so makes the dog's aggression the owner's liability.
Physical distress or illness
Dogs that seemingly attack unprovoked and uncharacteristically may be trying to tell owners something. You might get grouchy when you are not feeling well, and dogs often do the same. Aggression can be indicative of physical pain or illness and may necessitate a visit to the veterinarian.
Sometimes, dogs act out in reaction to provocation. Dogs are generally perceptive of tone and body language, so when people present themselves with hostility, a dog may respond accordingly. If a person goes so far as to provoke a dog verbally or physically through yelling or violence, it is even more likely that a dog will bite. Though such situations are complex, owners should always leash and restrain their dogs.
Regardless of the cause, if a dog has bitten you, you should seek out medical care as soon as possible. A bite left untreated can become infected and cause serious health complications.