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:

Post-traumatic stress disorder (PTSD) may occur soon after a major trauma, or it can be delayed for more than 6 months after the event. When it occurs soon after the trauma, it usually gets better after 3 months. However, some people have a longer-term form of PTSD, which can last for many years.

PTSD can occur at any age and can follow a natural disaster such as a flood or fire, or events such as war, a prison stay, assault, domestic abuse, or rape. The terrorist attacks of September 11, 2001, in the United States may have caused PTSD in some people who were involved, in people who saw the disaster, and in people who lost relatives and friends. These kinds of events can produce stress in anyone, but not everyone develops PTSD.

The cause of PTSD is unknown, but 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). Having been exposed to trauma in the past may increase the risk of PTSD.

Having good social support helps to protect against PTSD. In studies of Vietnam veterans, those with strong support systems were less likely to get PTSD than those without social support.

People with PTSD re-experience the event again and again in at least one of several ways. They may have frightening dreams and memories of the event, feel as though they are going through the experience again (flashbacks), or become upset during anniversaries of the event.