RE: 5 month old brittney
Many differ on this, but I feel strongly no dog should ever be allowed to bite, knaw or mouth people.
For a puppy that age it could just as easily be a subtle means of attempting dominance, in fact I would bet it is as dogs don't teeth on hands much.
I find the best way to address this is to when the pup goes to chew on your hand, role the skin of the muzzle between the teeth and your hand and then apply pressure. Do this EVERY time the dog goes to mouth you, and that should fix it in most cases. Some of the real hard headed ones will require a sharp rap on the nose (not to hard) anda stern "no" command every time they go to bite.
For everyone's sake, you don't want your dog to think it can apply teeth pressure to any person.