If everything I've read and watched is anything to go by, punching somebody in the head/face can sometimes cut up your hands on the pointy and sharp bits of the skull. You should only punch if you're familiar with those parts of the skull or have gloves on. Better off going with open hand slaps and palm strikes. Fists, elbows, knees and feet are for the torso, arms, legs, neck and groin; palms are for the face, and fingers are for the eyes. There are also a lot of places on the body where you can grab and bite, if you're so inclined.