Three nasal/oral sensory systems, which are anatomically and physiologically distinct, mediate smell, taste, and irritation. However, all three systems may be stimulated by food chemicals (which have "flavors" for the individual), and their receptors are located in adjacent oral and nasal cavities. The three sensory systems each have tiny cerebral cortical representations in humans, and interact with ventral forebrain areas attributed roles in affect and incentive. The complexity of these interactions makes it difficult for affected patients to identify readily which chemosensory system is malfunctioning.