It started with a thumb into my eye socket as he tried to gouge out my eye. When he bit into my ear, the adrenaline flooding my veins masked the pain; I would not even realize my ear was gone till after the fight. Twenty years ago, in that dimly lit alley in Kent, Washington, as I walked into a ring of teenage onlookers to face off, my heart was pounding so hard my chest hurt. My vision narrowed—I could only see faces—and I felt sick in my gut.

I'd been in the Army for a few years and had received just a few hours of hand-to-hand combat training. I was terrified. For the sake of pride or 19-year-old stupidity, I made the choice to fight and it cost me my left ear. But I've never forgotten the feeling I had that night, and in a way it's been useful to me. It gave me insight into the way my body responded, years later, when faced with two very different tours of combat in Iraq. And what I know from those experiences is that we are still far from understanding the effects of traumatic stress.

WIRED OPINION About Army Major John Spencer

(@spencerguard) is a scholar with the Modern War Institute at the US Military Academy in West Point. He is an infantry soldier with 23 years’ experi­ence, including two tours of combat in Iraq.

My body was reacting to extreme fear that night in Washington. Facing imminent danger, multiple brain regions launched a coordinated response, releasing stress hormones—adrenaline to speed the heart and respiration, cortisol to inhibit any systems not needed at the moment. This is the body’s evolutionary survival mechanism to increase the chances of either destroying the threat or escaping. Fight or flight.

But my experience of battle in Iraq during my first deployment in 2003 was actually different. Before patrols that led to firefights, I felt heightened anxiety, but I knew I was trained to respond and rarely doubted my ability to deal with the situation. Only toward the end of that tour did we begin to see a new weapon on the Iraqi battlefield: improvised explosive devices.

When I returned to Iraq in 2008, IEDs were much more pervasive, advanced, and destructive. For many weeks, soldiers in my unit were hit every day. Some attacks caused casualties, some didn't. I thought about the IEDs every time I got in a vehicle. I remember reaching for the door handle and experiencing the same sinking feeling in my gut I knew from that street fight—wondering, was this the day?

For much of the ride I felt like I was waiting for a punch to the face. At spots on the road that looked like they could hold an IED, or where one had exploded in the past, my heart rate spiked and I felt nauseous. It was the same fight-or-flight response, but there was no one to fight and no way to escape. Every drive was a game of Russian roulette, and there was little I could do to improve the odds.

All soldiers experience combat stress in battle. But not all soldiers engage in what is commonly thought of as battle—fighting the bad guys. Even those whose job it is may rarely get the chance; there's an old saying that war is long periods of boredom punctuated by moments of terror. However, in Iraq, all of us, even those not in combat arms jobs, faced that terror on a daily basis. And while an infantryman’s training helps to manage the stress of a firefight, there is no training for waiting to be blown up by a roadside bomb.

Perhaps the type and duration of combat stress these soldiers faced was something new. The problem is, no one knows.

We know that chronic exposure to stress hormones alters brain structures involved in cognition and mental function­ing. Not surpris­ingly, a 2011 report from the Congressional Budget Office found that 27 per­cent of vets receiving care from the VHA after tours in Iraq and Afghanistan were diagnosed with post-traumatic stress disorder—much higher than estimates for previous wars. The annual cost of treatment is said to be in the billions.

The rise in diagnoses could be due in part to increased awareness and a greater willingness among service mem­bers to report their problems. But it could also be that the type and duration of combat stress these soldiers faced was something new. The problem is, no one knows. Very little research has been done on just how stress becomes physical damage, for the obvious reason: You can only really study trauma where it's incurred, on the battlefield.

One of the last major efforts to analyze the physiological response to combat was undertaken during the Vietnam War. In 1966, Army researchers collected blood and urine samples from Special Forces soldiers who faced over­whelming Vietcong forces near the Cambodian border. They observed how stress hormones built up in anticipation of an attack and dropped afterwards.

But there is so much we still don't know. Why do some people who are exposed to stress hormones suffer psycho­logical scarring while others don't? How do the effects accumulate? How many days of intense stress are too many? Is the constant fear of an insidious, unseen danger worse than episodic battles? Does it make a difference if you feel there's something you can do to try to stay alive?

These are questions we need answers to. We’ve gotten smarter about treating the symptoms of PTSD. But if we better understood its genesis, we might find ways of stem­ming the damage at its source. To truly reduce the harmful long-term effects of stress, I believe the military must do research on the battlefield, before soldiers become patients. We need scientific boots on the ground.

This would not be an easy mission, but the benefits could be immense—and not just for soldiers. After all, it’s not only in war that people cope with anxiety. Police officers may experience chronically elevated levels of stress hormones. Victims of crime or abuse, those who live in poverty or fear of losing their job, populations threatened by terrorism—traumatic stress is a universal human problem. But we in the armed services are in a position to do something about it.

PTSD is real. It’s challenging, vicious, and unrelenting. And until we understand it better, we will fail to provide the best possible care for those who suffer from invisible wounds.