When you reach to grab a hot pan on the stove, your hand automatically pulls away before you even realize it's hot or that you were burned. We humans respond to trauma using that same part of the brain responsible for processing danger, explains Cedars-Sinai clinical psychologist Megan Auster-Rosen, PsyD.

"Your body reacts first," she says. "The rest is us just catching up to what happened."

Trauma's footprint is better understood than ever before: 61% of men and 51% of women experience at least one traumatic event in their lifetimes, according to the Substance Abuse and Mental Health Services Administration. These prevalent experiences rewire the brain and body, leaving survivors vulnerable to health conditions for decades. From the immune system to the gut, their physiological effects are far-reaching.

In the wake of widespread uncertainty and loss amid the COVID-19 pandemic, wildfires and mass shootings, trauma awareness is growing. Still, not every negative experience results in trauma. Instead of painting the condition with a broad brush, mental health providers are looking closely at different types, risk factors and treatments for its more severe, complicated outcomes.

Trauma has become a buzzword—but it can't be assigned to any instance of hurt feelings.

A traumatic event creates a deep sense of fear, helplessness or disorientation and overwhelms a person’s ability to cope. The American Psychological Association notes a long-term negative impact on functioning and beliefs, especially challenging a person's "view of the world as a just, safe and predictable place."

The roots of trauma can include actual or threatened serious injury or death, major illness, accidents, military combat, interpersonal violence such as sexual violation or abuse, as well as dangerous natural occurrences like earthquakes.

An event doesn't have to happen to you directly—you can be traumatized by witnessing it, learning that a loved one experienced it or facing "repeated or extreme exposure to details of the event," Dr. Auster-Rosen says.

Read: Coping With Complicated Grief

Dangerous experiences create a "fight-or-flight" acute stress response that spikes heart rate and blood pressure and releases the stress hormone cortisol. They also mobilize an inflammatory immune defense.

Many survivors become jumpy, constantly looking for threats. Being on edge all the time can interfere with normal processes that come naturally when you feel safe. You might be too scared to fall asleep. And since your energy is focused on immediate risks, your gastrointestinal system will often skip digestion. In turn, you might have frequent bowel movements.

"Your body is anticipating that it's going to have to defend itself at any moment," Cedars-Sinai psychiatrist Scott Campbell, MD, explains.

Avoiding reminders is also common after a traumatic event. Sometimes that means checking out emotionally or numbing with alcohol because the experience is too disturbing to process.

Mental health experts point out that people usually have a combination of these responses, which humans evolved to try to survive.

But if they continue or get worse after a month, that signals post-traumatic stress disorder (PTSD). You're at higher risk of PTSD if you have already experienced trauma, especially in childhood or over time, or if you or your family have existing mental health disorders.

The National Center for PTSD says about 12 million U.S. adults develop the condition every year.

"When you undergo trauma, your body senses danger and sets off all those different alarms that in the moment are really important," Dr. Auster-Rosen says. "Over time, though, they are actually not so good for you."

We get stuck reliving the event that left us helpless and trying to overcome it, experiencing flashbacks, nightmares, intrusive thoughts and reactivation. In turn, stress and immune responses continue to cycle.

When you store psychological stress in the body, muscles often involuntarily tighten, leading to chronic tension headaches, exhaustion and musculoskeletal pain—and potentially fibromyalgia, or pain in muscles and soft tissues all over the body. Prior and repeated trauma is linked to the persistent pain condition.

Providers regularly see patients for irritable bowel syndrome or ulcerative colitis symptoms that aren't improving with treatment. They may find later that the patient has underlying psychological distress that's either causing or contributing to the GI tract irritation, Dr. Campbell says. Frequent bowel movements that are common in fight-or-flight over time can lead to IBS.

Others who already have medical conditions like tinnitus (ringing in the ears) can have their symptoms worsen.

Dr. Campbell has also seen patients develop sudden-onset conversion disorder—when psychological conflict shows up as a neurological condition such as blindness or stroke-like symptoms.

Trying to run away from difficult memories can backfire.

"This experience isn't ever going to be erased, so when you ignore it, it's still there," Dr. Auster-Rosen says. "It's just going to rear its head in a variety of different ways until you actually face it."

The long-term fallout extends to the entire body.

The immune system's inflammatory activation might speed up aging—and is tied to cardiovascular, memory, skin, nervous system and autoimmune disease. A landmark 2018 study of 41 different autoimmune conditions determined that people with post-traumatic stress were more likely to develop the disorders including rheumatoid arthritis, Crohn's disease, psoriasis and multiple sclerosis.

Read: PTSD From COVID-19? What You Should Know

Psychiatric medications stabilize a person's anxiety centers. Lowering reactivity can help a patient "regulate enough to actually deal with trauma in a slow way," Dr. Campbell suggests.

"Traumatic stress is like being stuck in this moment that you couldn't process," he explains. "It lives to terrorize you until you actually take the trauma down off the shelf and go through it with somebody in a very controlled way."

Psychologists unpack trauma with talk therapy focused on reframing unhelpful thoughts and beliefs—such as shame after abuse—and learning coping skills. Other PTSD therapies such as somatic experiencing are body-based, teaching patients to better understand and regulate their physical reactions to stressful triggers (including smells and sounds). The trauma resiliency model uses the mind-body connection to first improve physical sensations like pain and fatigue, then heal emotionally. Many treatments also expose the patient to the experience they survived to reprocess it. 

Therapies addressing emotions and the body are effective in combination, psychologists say.

"The most important thing is rapport between the patient and clinician," Dr. Auster-Rosen emphasizes. "If the clinician can create trust and a safe space, then the work can be done. If not, then the work cannot be done, no matter the modality."

Scientists are delving into techniques to predict and prevent survivors' likelihood of developing severe responses such as PTSD or even suicide. One potential option is prescribing propranolol beta blockers in the aftermath of a scary assault or accident to slow a patient's heart rate and calm their sympathetic nervous system. Selective serotonin reuptake inhibitors (SSRIs) have been shown to lower autoimmune risk if used in the year immediately after a traumatic event as well.

Further research is exploring ways to minimize harm among people facing chronic workplace stressors—such as healthcare workers during the pandemic.

Providers point to growing recognition of the role of trauma-informed care outside of traditional mental health settings. When a patient is being treated for headaches or other stress-associated symptoms with little success, doctors need to be aware of any underlying trauma that could make the difference.

"Trauma compartmentalizes you," Dr. Auster-Rosen notes, "but you can't heal its effects piecemeal. Much of the work is about integrating the experience and feeling whole again."