How positive, tolerable, and toxic stress impact the developing brain.

Three types of stress response

Stress is one of the factors that shapes brain architecture in a developing child, but not all stress is the same. Whether it strengthens or weakens brain architecture has to do with the intensity of the stress, its duration, and whether supportive caregivers are present in the child’s life. 


Not all stress is bad. Small challenges that create “positive stress”—like meeting new people or starting the first day of school—are healthy for development because they help prepare young brains and bodies for the larger challenges they will meet in the future.


More serious events, like a natural disaster or losing a loved one, aren’t good for us. But if supportive caregivers are around to buffer the child’s stress response, these situations won’t do lasting damage to the brain. That’s called "tolerable stress." 


The last kind of stress experience is called “toxic stress” because it weakens brain architecture and can disrupt healthy development. Toxic stress occurs when no supportive caregivers are around to buffer a child’s response to repeated negative experiences. Things that cause toxic stress may include abuse, neglect, parental addiction or mental illness, violence in or outside the home, and chaotic environments. Young children whose brain development has been disrupted by toxic stress are at a much higher risk for later physical and mental health problems, including developing a mental illness such as depression, anxiety, or addiction.


Toxic stress can harm the brain at any point in development, but when it occurs early and affects foundational circuits, the impacts can be even more profound. Because toxic stress can affect lifelong learning, social abilities, and health outcomes, it’s important to intervene early.  

Research in Alberta shows that the most common triggers of toxic stress in children are:

  • Parental mental illness
  • Parental substance abuse
  • Parental abandonment or divorce
  • Emotional abuse
  • Sexual abuse  
  • Physical abuse
  • Witnessing domestic violence
  • Emotional neglect
  • A family member in prison
  • Physical neglect


There are two important ways to intervene on behalf of children experiencing toxic stress. First, adults can help soothe children who are upset, calm their emotions, and help their stress response system come back to normal levels. Second, adults can help teach children healthy coping skills to deal with stress later on.

The second kind of intervention involves prevention: targeting the source of toxic stress so that it doesn’t continue. This approach involves helping the caregivers. An intervention for a parentsuch as support to leave an abusive relationship or receiving quality addiction treatmentis also an intervention for the child, who will no longer experience the stressful effects of witnessing abuse or parental addiction.

Evidence suggests the most effective interventions support caregivers and children both individually and through activities they work on together to strengthen their relationship. 

The Science of Stress

The stress response begins and ends in the brain. When we perceive a threat in our environment, the brain releases a cascade of stress hormones such as adrenalin and cortisol that prepare us for a “fight or flight” response. These hormones quicken the heartbeat, shut down non-essential biological systems, shunt available energy to our muscles, alter our metabolism, and focus the mind on the immediate threat. Cortisol is also involved in shutting down the stress response: once the threat is gone, cortisol signals the brain’s stress circuits to shut down the production of hormones.

When stress hormones remain elevated over long periods of time, they produce wear and tear on the brain and certain biological systems, which are not designed to operate under constantly stressful conditions. In addition, cortisol in high concentrations is in itself damaging to biological tissues and can affect the stability of new brain circuits as they are forming. If cortisol levels remain high for long periods of time, the brain and body make adaptations to try to achieve balance in the system. This effect, which is called allostasis, can affect how our stress system regulates the stress response: the brain becomes less sensitive to the effects of cortisol such that it becomes harder to shut down our stress response system over time. Allostatic load refers to the degree to which our brains and bodies try to adapt to chronically high stress hormones; a high allostatic load is associated with vulnerability to health problems later in life.

Supportive environments for children are key, both to reduce their exposure to toxic stress and to create buffers of support to make stressful life events more tolerable.

Community Support: Pay Now or Pay Later

Trying to build new skills on a foundation of unstable brain circuits requires more work and is less effective than establishing strong brain architecture from birth. Although our brains retain the capacity to change and adapt even as we age, remedial education, clinical treatment, and other professional interventions are more costly, take more time, and produce less desirable outcomes than getting it right the first time through the provision of nurturing, protective relationships and appropriate learning experiences earlier in life. Better life outcomes could be achieved by decreasing the number and severity of adverse childhood experiences and by strengthening the relationships that protect young children from the harmful effects of toxic stress. It is important to remember that, when needed, providing services and supports for a caregiver in need isn't just an intervention for the benefit of that individual—it's an intervention for families and communities as well.

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