Illness onset

How is illness onset relevant to PTSD?

Differences are observed in the age of onset of mental disorders, which may be influenced by genetic and/or environmental factors. While most individuals develop symptoms of PTSD within three months of the trauma, some symptoms can appear later and persist for months and sometimes years. Understanding the factors associated with the onset of symptoms could lead to better understanding of the disorder and earlier and improved intervention strategies for patients.

What is the evidence for illness onset of PTSD?

Moderate to high quality evidence finds the average age of onset of PTSD is 26.6 years, with no differences between males and females.

The overall median prevalence of PTSD tends to reduce over time, from 28.8% at one-month post trauma to 17% at 12 months post trauma. Median prevalence post non-intentional (accidental) trauma also decreases over time (30.1% to 14%), while median prevalence post intentional (non-accidental) trauma is lower initially and increases over time (11.8% to 23.3%).

Around 24.5% of people diagnosed with PTSD had a delayed onset of illness, with most experiencing earlier milder symptoms. The prevalence of delayed-onset PTSD is highest in professional groups and those who experienced combat trauma.

August 2021

Image: ©Katarzyna Bialasiewicz –

Last updated at: 4:22 am, 31st July 2021
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