When people are confronted with unpleasant and potentially harmful stimuli such as foul odors or tastes, PET-scans show increased bloodflow in the amygdala. In these studies, the participants also reported moderate anxiety. This might indicate that anxiety is a protective mechanism designed to prevent the organism from engaging in potentially harmful behaviors.
Anxiety can be caused by numerous factors, ranging from external stimuli, emotional abandonment, shame, to experiencing an extreme reaction when first exposed to something potentially anxiety-provoking. Research has not yet explained why some people will experience a panic attack or develop a phobia, while others growing up in the same family and shared experiences do not. It is likely that anxiety disorders, like all mental illness, is caused by a complex combination of factors not yet fully understood. These factors likely include childhood development, genetics, neurobiology, psychological factors, personality development, and social and environmental cues.
Occasional anxiety is an expected part of life. You might feel anxious when faced with a problem at work, before taking a test, or before making an important decision. But anxiety disorders involve more than temporary worry or fear. For a person with an anxiety disorder, the anxiety does not go away and can get worse over time. The symptoms can interfere with daily activities such as job performance, school work, and relationships.