Post-traumatic stress disorder - Causes of post-traumatic stress disorder (PTSD)

Post-traumatic stress disorder (PTSD) can develop after a very stressful, frightening or distressing event, or after a prolonged traumatic experience.

Types of events that can lead to PTSD include:

• serious road accidents
• violent personal assaults, such as sexual assault, mugging or robbery
• prolonged sexual abuse, violence or severe neglect
• witnessing violent deaths
• military combat
• being held hostage
• terrorist attacks
• natural disasters, such as severe floods, earthquakes or tsunamis

PTSD is not usually related to situations that are simply upsetting, such as divorce, job loss or failing exams.

PTSD develops in about 1 in 3 people who experience severe trauma. It is not fully understood why some people develop the condition while others don't, but there are factors that appear to make certain people more likely to develop PTSD.

If you've had depression or anxiety in the past, or you don't receive much support from family or friends, you are more susceptible to developing PTSD after a traumatic event.

There may also be a genetic factor involved in PTSD. For example, having a parent with a mental health problem is thought to increase your chances of developing the condition.

Possible causes

Although it is not clear exactly why people develop PTSD, a number of possible reasons have been suggested. These are described below.

Survival mechanism

One suggestion is that the symptoms of PTSD are the result of an instinctive mechanism intended to help you survive further traumatic experiences.

For example, the flashbacks many people with PTSD experience may occur to force you to think about the event in detail so you are better prepared if it happens again, and the feeling of being "on edge" (hyperarousal) may develop to help you react quickly in another crisis.

However, while these responses may be intended to help you survive, they are actually very unhelpful in reality because they mean you can't process and move on from the traumatic experience.

Adrenaline levels

Studies have shown that people with PTSD have abnormal levels of stress hormones.

When in danger, the body produces these hormones, such as adrenalin, to trigger a reaction in the body. This reaction, often known as the "fight or flight" reaction, helps to deaden the senses and dull pain.

However, people with PTSD have been found to continue to produce high amounts of fight or flight hormones even when there is no danger. It is thought this may be responsible for the numbed emotions and hyperarousal experienced by some people with PTSD.

Changes in the brain

In people with PTSD, parts of the brain involved in emotional processing appear different in brain scans.

One part of the brain responsible for memory and emotions is known as the hippocampus. In people with PTSD, the hippocampus appears smaller in size. It is thought that changes in this part of the brain may be related to fear and anxiety, memory problems and flashbacks.

The malfunctioning hippocampus may prevent flashbacks and nightmares from being properly processed, so the anxiety they generate does not reduce over time.

Treatment of PTSD results in proper processing of the memories so, over time, the flashbacks and nightmares will gradually disappear.