We all know how stress can make us feel. Our hearts start racing, we break out in a sweat, we get a headache, etc. These are the body’s, immediate responses to a tense moment. Over time, however, stress can have a much more significant, far-reaching impact on both the body and the mind.

Stress is an automatic physiological response to any situation that is threatening, overwhelming or requires adjustment to change. The stress response includes many physical changes, including increased heart rate and breathing, and inhibited digestion and immune response, triggered by stress hormones released in response to real or perceived danger (i.e., fight, flight, freeze).

This survival-based alarm system helped our primitive ancestors deal with their environment. When they encountered danger, they had extra energy and strength to attack or escape. When the danger passed, the stress response would abate. However, when the stress response is chronically triggered, such as during childhood maltreatment and compromised attachment, key biological systems become altered and dysregulated. Chronic stress is linked not only to many mental health problems, such as anxiety and depression, but also to numerous physical health problems, including heart disease, ulcers, and asthma.

3 Components of the Stress Response


There are three interrelated components of the human stress response: catecholamines, HPA axis, and immune system response.

  1. Catecholamines – These include epinephrine, norepinephrine, and dopamine, which are released by the sympathetic nervous system in response to threat.
  2. The hypothalamic–pituitary–adrenal (HPA) axis – This system responds with a cascade of stress biochemicals. The hypothalamus releases corticotropin-releasing hormone (CRH), which triggers the pituitary to release adrenocorticotropic hormone (ACTH), finally causing the adrenal glands to activate the flow of cortisol, raising the blood glucose level to respond to threat.
  3. The immune system – This is part of the third portion of the stress response. Elevated levels of stress hormones depress immune function. Under normal conditions, the immune system releases proinflammatory cytokines, which increase inflammation to help the body heal wounds and fight infection. Severe and chronic stress causes inflammation levels to be abnormally high, resulting in vulnerability to physical problems and disease.


Research on Psychoneuroimmunology (PNI), which focuses on the mind-body connection, has found that people who suffer trauma have higher rates of serious illnesses than the general population.

The Adverse Childhood Experiences (ACE) study found that adults who experienced trauma and disrupted attachment as children—including physical and sexual abuse, and parental mental illness, substance abuse, and criminal behavior—had higher rates of cancer, heart disease, bronchitis, diabetes, stroke, and gastrointestinal disorders, than non-traumatized adults.

Similar outcomes have been found in other studies: women maltreated as children had a nine-fold increase in heart disease; 60 percent of women treated for gastrointestinal illness had an abuse history; significantly higher rates of chronic pain, chronic fatigue syndrome, and fibromyalgia occurred when there was a history of trauma and PTSD diagnoses.

This article is part of our Biology Series in which we take a closer look at mind-body-emotion connections. Learn more about the full series here.