Many of us will experience some kind  of trauma during our lifetime. Sometimes, we escape  with no long-term effects. But for millions of us,  those experiences linger, causing symptoms like flashbacks, nightmares, and negative thoughts  that interfere with everyday life. This phenomenon,  called post-traumatic stress disorder, or PTSD, isn’t a personal failing; rather, it’s a treatable malfunction  of certain biological mechanisms that allow us to cope  with dangerous experiences. To understand PTSD, we first need to understand how the brain  processes a wide range of ordeals, including the death of a loved one, domestic violence, injury or illness, abuse, rape, war, car accidents, and natural disasters. These events can bring on feelings  of danger and helplessness, which activate the brain’s alarm system, known as  the “fight-flight-freeze” response. When this alarm sounds, the hypothalamic, pituitary,  and adrenal systems, known as the HPA axis, work together to send signals  to the parasympathetic nervous system. That’s the network that communicates  with adrenal glands and internal organs to help regulate functions like heart rate, digestion, and respiration. These signals start a chemical cascade that floods the body with several  different stress hormones, causing physiological changes  that prepare the body to defend itself. Our heart rate speeds up, breathing quickens, and muscles tense. Even after a crisis is over, escalated levels of stress hormones  may last for days, contributing to jittery feelings, nightmares, and other symptoms. For most people, these experiences disappear within a few days to two weeks as their hormone levels stabilize. But a small percentage of those who experience trauma have persistent problems —sometimes vanishing temporarily  only to resurface months later. We don’t completely understand  what’s happening in the brain, but one theory is that  the stress hormone cortisol may be continuously activating  the “fight-flight-freeze” response while reducing overall brain functioning, leading to a number of negative symptoms. These symptoms often fall  into four categories: intrusive thoughts,  like dreams and flashbacks, avoiding reminders of the trauma, negative thoughts and feelings, like fear, anger, and guilt, and “reactive” symptoms like irritability  and difficulty sleeping. Not everyone has all these symptoms, or experiences them to the same extent  and intensity. When problems last more than a month,  PTSD is often diagnosed. Genetics, on-going overwhelming stress, and many risk factors  like preexisting mental illnesses or lack of emotional support, likely play a role in determining  who will experience PTSD. But the underlying cause  is still a medical mystery. A major challenge of coping  with PTSD is sensitivity to triggers, physical and emotional stimuli that the brain associates  with the original trauma. These can be everyday sensations  that aren’t inherently dangerous but prompt powerful physical  and emotional reactions. For example, the smell of a campfire could evoke the memory of being trapped  in a burning house. For someone with PTSD, that memory activates the same neurochemical cascade as the original event. That then stirs up the same feelings  of panic and helplessness as if they’re experiencing  the trauma all over again. Trying to avoid these triggers, which are sometimes unpredictable, can lead to isolation. That can leave people feeling invalidated, ignored, or misunderstood, like a pause button has been pushed on their lives while the rest of the world  continues around them. But, there are options. If you think you might  be suffering from PTSD, the first step is an evaluation  with a mental health professional who can direct you towards  the many resources available. Psychotherapy can  be very effective for PTSD, helping patients better  understand their triggers. And certain medications  can make symptoms more manageable, as can self- care practices, like mindfulness and regular exercise. What if you notice signs of PTSD  in a friend or family member? Social support, acceptance, and empathy are key to helping and recovery. Let them know you believe their account of what they’re experiencing, and that you don’t blame them  for their reactions. If they’re open to it, encourage them to seek evaluation  and treatment. PTSD has been called “the hidden wound” because it comes  without outward physical signs. But even if it’s an invisible disorder,  it doesn’t have to be a silent one.