The causes of anxiety disorders can be attributed to the following:

Changes in the brain

When conditions that evoke anxiety are experienced by those with the disorder, they typically see hyperactivity in the amygdala – a region of the brain responsible for fear and related emotional processes, including fear conditioning, reward learning, and processing of emotional events. This region is not only more active but responds faster to anxiety-provoking situations in individuals with anxiety disorder. Other regions of the brain may also contribute to anxiety disorders. The anterior cingulate cortex and the insula, also known as the “fear network”, contributes to the development and maintenance of anxiety disorders .  The anterior cingulate cortex is important in fear avoidance, while the insula processes emotions and awareness of internal distress.

In the case of posttraumatic stress disorder (PTSD) , the hippocampus, a region of the brain responsible for forming memories, demonstrates low activity during exposure to PTSD triggers. Changes in the structure of the hippocampus, amygdala, and medial prefrontal cortex  (a brain region involved in decision making)  have also been observed.

Environmental Stress

There are numerous environmental factors that can contribute to the development of anxiety disorders. One of the most common is stress, especially stress for a long period of time, due to a major traumatic life event such as an unhealthy relationship or a highly stressful job.

Upbringing can also contribute to anxiety disorders. Those who were taught to respond to certain situations with fear, or who were overly stressed about interactions and performance in school, are likely to develop anxiety disorders.

Traumatic events such as near death experiences, sexual assault, or witnessing a violent act can also trigger some anxiety disorders. Major life changes such as a new job or the death of a close relative or friend can also lead to the development of anxiety disorders.

Genetics

Anxiety can be inherited and while no specific genes have been linked to anxiety disorders, genetic variations have been observed among twins with differing levels of anxiety.