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Causes - Post-traumatic stress disorder (PTSD)

Post-traumatic stress disorder (PTSD) can develop after a very stressful or distressing event. It can also develop after continued exposure to traumatic experiences.

The types of events that can lead to PTSD include:

  • serious road accidents
  • violent personal assaults, such as sexual assault, mugging or robbery
  • continued 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 caused by situations such as a divorce, job loss or failing exams. These can be difficult, but you are unlikely to develop PTSD as a result.

It is not fully understood why some people develop the condition while others do not. But certain factors can 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
  • do not receive much support from family or friends
  • have a parent with a mental health problem

Reasons people develop PTSD

It's not clear exactly why people develop PTSD. But there are some possible reasons.

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.

These responses may have developed for survival. But in some cases they do not help. Especially if you are constantly on edge, predicting a need to try and survive a catastrophic event in everyday situations.

High adrenaline levels

People with PTSD can have increased levels of stress hormones.

When in danger, the body normally 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 why some people with PTSD have symptoms like numbed emotions and hyperarousal.

Changes in the brain

The part of the brain responsible for memory and emotions is the hippocampus. In people with PTSD, the hippocampus appears smaller in size.

When the hippocampus does not work properly it can mean flashbacks and nightmares are not properly processed. This means the anxiety they generate does not reduce over time.

Treatment of PTSD can help you to properly process 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: 1 September 2022
Next review due: 1 September 2025