Dog aggression towards Humans
Fear Induced aggression:
Fear is the most common reason for dogs to bite strangers or people outside the immediate family. Dogs do not need to have had painful or frightening experiences with such people to become afraid. Undersocialized dogs are likely to be fearful simply because they did not meet enough people and have pleasant experiences with them while they were young.
While a puppy is young and shy, he will try to appease, hide behind his owner if he can, or run away from frightening situation. As he matures he will become more confident of his own ability to defend himself. In stressful situations from which he has learned there is no escape (for example, when on the leash) he may start to use aggression to try to make the threat go away. Once he finds out how effective this is, the aggressive displays often behind to get worse, until bites occur.
Members of the family who use force and punishment in an attempt to train a puppy are also likely to be viewed with mistrust, as are children who tease or torment puppies, and they are likely to be bitten during confrontations when the dog feels a need to defend itself.
Socialization is the key to preventing fear aggression. Do not force a puppy into a situation that he is obviously unhappy about. Allow him time to get brave enough to go forward and investigate, and try to make the experience a pleasurable one by using toys and tidbits. If he is restricted by the leash, or is backed into a corner, help him out by removing the source of his fear so that he does not learn to be aggressive in order to solve the problem. Remember it is your responsibility, as a pack leader, to protect pack members from harm and help them out of difficult situations, even if this means asking a well meaning person who is trying to get your puppy's attention not to do so.
Ensure that all unavoidable upsets are countered with many happy experiences in the same situation. If dogs consider all humans, adults and children, to be a source of fun, treats, and games, they will not want to chase people away with threatening displays of behaviour.
If you have a shy puppy you will need to work harder than someone with an outgoing puppy. Your puppy should be sociable and friendly with everyone he meets before you can relax your socialization program a little.