Stress and Your Brain: Working Towards Wellbeing

The National Institute of Mental Health defines stress as simply “the brain’s response to any demand.” Given that definition, not all stress is bad. It is simply a response. How harmful it ultimately depends on its intensity, duration and treatment.
 
Stress takes a variety of forms. Some stress happens as the result of a single, short-term event — having an argument with a loved one, for example. Other stress happens due to recurring conditions, such as managing a long-term illness or a demanding job. When recurring conditions cause stress that is both intense and sustained over a long period of time, it can be referred to as “chronic” or “toxic” stress. While all stress triggers physiological reactions, chronic stress is specifically problematic because of the significant harm it can do to the functioning of the body and the brain.
https://www.tuw.edu/health/how-stress-affects-the-brain/