Definition of Post-traumatic stress disorder:

Post-traumatic stress disorder is a type of anxiety disorder. It can occur after you've seen or experienced a traumatic event that involved the threat of injury or death.

Causes, incidence, and risk factors:

PTSD can occur at any age. It can follow a natural disaster such as a flood or fire, or events such as:

• Assault
• Domestic abuse
• Prison stay
• Rape
• Terrorism
• War

For example, the terrorist attacks of September 11, 2001 may have caused PTSD in some people who were involved, in people who saw the disaster, and in people who lost relatives and friends.

Veterans returning home from a war often have PTSD.

The cause of PTSD is unknown. Psychological, genetic, physical, and social factors are involved. PTSD changes the body's response to stress. It affects the stress hormones and chemicals that carry information between the nerves (neurotransmitters).

It is not known why traumatic events cause PTSD in some people but not others. Having a history of trauma may increase your risk for getting PTSD after a recent traumatic event.