It is not yet completely understood why certain people develop PTSD after a traumatic experience, and others do not. However, there are some risk factors which seem to make PTSD more likely to happen to some people. For example, if you have already had depression or anxiety, or you have not had a lot of support from family or friends, you are more susceptible to the condition.

Having a parent who had a mental health problem or experiencing abuse as a child can also be risk factors.

There may also be a genetic factor involved, so some people will be more likely to develop PTSD. The hippocampus (part of the brain that is important to memory and emotions) appears different in MRI scans in those with PTSD. Researchers believe that changes to the hippocampus are related to memory problems and flashbacks.

Studies have also shown that in people with PTSD, there are abnormal levels of hormones involved in their response to stress. People in danger normally produce natural opiates. These chemicals trigger a reaction in the body when put under extreme stress or into a fight or flight situation. They deaden the senses and dull the pain. It has been found that people with PTSD continue to produce high levels when there is no danger. This may cause them to have feelings of detachment and blunted emotions.