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Post-traumatic stress disorder (PTSD)

Post-traumatic stress disorder (PTSD): Causes

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

The 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
  • a diagnosis of a life-threatening condition
  • an unexpected severe injury or death of a close family member or friend

PTSD is not usually related to situations that are simply upsetting. For example, a divorce, job loss or failing exams. These can be difficult but you are unlikely to develop PTSD as a result.

It isn't fully understood why some people develop the condition while others don't. But certain factors appear to make some people more likely to develop PTSD.

Who's at risk

You're more at risk of developing PTSD after a traumatic event if you:

  • have had depression or anxiety in the past
  • don't receive much support from family or friends
  • have a parent with a mental health problem

Reasons PTSD develops

Although it's not clear exactly why people develop PTSD, a number of possible reasons have been suggested.

Survival mechanism

One suggestion is that PTSD is there to help you survive further traumatic experiences. For example, the flashbacks you have with a PTSD experience may force you to think about the event in detail. This is supposed to make you better prepared if it happens again. The feeling of being "on edge" (hyperarousal) may develop to help you react quickly in another crisis.

While these responses may be intended to help you survive, they're actually unhelpful. It means you can't process and move on from the traumatic experience.

High adrenaline levels

People with PTSD have abnormal levels of stress hormones.

Normally, when in danger, the body produces stress hormones such as adrenaline. This triggers a reaction in the body. This is the "fight or flight" reaction. It helps to deaden the senses and dull pain.

People with PTSD continue to produce high amounts of fight or flight hormones. This happens even when there's no danger. This may be responsible for the numbed emotions and hyperarousal experienced by some people with PTSD.

Changes in the brain

Parts of the brain of people with PTSD appear different in brain scans.

The part of the brain responsible for memory and emotions is the hippocampus. In people with PTSD, the hippocampus appears smaller in size. It's thought that changes in this part of the brain may link to fear and anxiety. It may also link to memory problems and flashbacks.

The malfunctioning hippocampus may prevent flashbacks and nightmares from being properly processed. This means the anxiety they generate doesn't reduce over time.

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

Content supplied by the NHS and adapted for Ireland by the HSE.

Page last reviewed: 23/09/2018
Next review due: 23/09/2021

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