Dog mouths are the equivalent of human hands. Happy people use their hands to pat a head or tickle a chin. Similarly, contented canines nuzzle and lick to convey affection or curiosity. In both species, however, some use these instruments to communicate in harmful ways, ranging from annoyingly bossy to dangerously aggressive ones.
Dogs act aggressively when they are uncomfortable with a situation, and may growl to indicate their fear and frustration.
If your dog is growling at you, see if you can understand why. Is he growling when you interrupt his feeding, napping, or during a chewing frenzy? Here, his growls are saying, "I want to be left alone." The next time the situation arises, offer him a treat as you approach to show him that you come in peace. Alternatively, is your dog growling while playing? As with kids, when dogs play, they express a lot of emotion, and your dog may simply be yapping playfully.