Black pigmentation on the nose and eye rims is traditionally preferred, with only some pink allowed. Socialization of this breed is paramount: this breed should never be left alone, bored, in a house or garage day after day, as it may become chronically fearful and aggressive towards things it does not know or understand. Some health problems in American bulldogs are often found within certain genetic lines, and are not common to the entire breed, while others, such as neuronal ceroid lipofuscinosis (NCL), Ichthyosis, disorders of the kidney and thyroid, ACL tears, hip dysplasia, cherry eye, elbow dysplasia, entropion, ectropion, and bone cancer are more common to the general population of American Bulldogs.