Post traumatic stress disorder, or PTSD, is an anxiety disorder that affects up to 30% of soldiers returning from Iraq. That’s according to a June 2010 study by Army medical researchers. Its results were that: “Prevalence rates for PTSD or depression with serious functional impairment ranged between 8.5% and 14.0%, with some impairment between 23.2% and 31.1%.”

If you or someone you know is troubled by PTSD, find out how to get help here.

For the latest on what scientists know about PTSD, EarthSky spoke with Paula Schnurr. She’s deputy executive director of the VA’s National Center for Post Traumatic Stress Disorder. She said PTSD involves changes in a person’s psychological state and their neurobiological state

Paula Schnurr: That is, their brain changes. The systems in the brain that help us deal with stress and regulate fear and emotional responding are changed as you might expect in response to the extreme trauma of combat.

Dr. Schnurr said that it’s normal for people exposed to a life-threatening event, to experience fear, shock and horror in the hours or days that follow. People may be flooded with memories of the event. They may have trouble falling asleep, or have nightmares. But most of the time, Schnurr said, these symptoms are natural. It’s when they persist past 30 days and the anxiety remains strong, there is a problem. But she said there’s hope.

Paula Schnurr: The first thing is that, not all soldiers have PTSD. Even soldiers and other military personnel who have problems readjusting to society, well that’s normal. And it can take some time. The second thing is that we have effective treatments.

Dr. Schnurr said that most people exposed to a traumatic event such as combat don’t develop PTSD. But certain factors make a person more or less likely to develop it.

Paula Schnurr: Probably the most important factor is the nature of the combat or the traumatic event. The more severe it is, whether someone’s injured, how long it lasts, how many times it occurs, increases the risk.

She said that what happens after a person’s been traumatized also make a difference.

Paula Schnurr: A supportive recovery environment, the absence of stress and further traumas can all be protective. Conversely, returning to further stressors, having additional traumas, marital difficulties, job problems and the like can make things more difficult.

She said that the experiences a person has had leading up to deployment to a war zone or any kind of event can make a person more or less likely to develop PTSD.

Paula Schnurr: One factor is the person’s age. Up to early adulthood, the younger a person is, the more likely they are to develop PTSD. The more education they have, the less likely. If they’ve had childhood stressors and trauma, they’re more likely. The way that I think about it, at least, is that part of what a person has to do when a person has experienced a trauma is to try to make sense of it. And a person who’s had more education, who is a little bit older, would have greater cognitive abilities to try to make meaning out of this horrible event.

Another thing scientists know, said Schnurr, is that the more severe the exposure, the greater the risk of PTSD.

Paula Schnurr: One of the more significant findings of this war is how multiple deployments matters. So we’ve had some military personnel who’ve been deployed three, perhaps even four times. These individuals are at particular risk because they’ve essentially experienced more and more severe trauma.

We asked her what scientists know today on preventing PTSD from developing in soldiers.

Paula Schnurr: This war has given us great opportunities to learn more about the effects of being exposed to a war zone, because we’ve been able to study people before, during and after they are deployed. In prior wars, for example Vietnam, we only studied people after. This is giving us an opportunity to try to evaluate prevention strategies. However, at this point, the state of the science is still evolving. And I can’t say definitively, I don’t think the field can definitively say how to prevent PTSD.