Stress is a natural response to danger. All animals exhibit stress. It is manifested as the hormone cortisol in the bloodstream. Cortisol shuts down non-essential operations so that the animal can escape the danger. One of them is digestion, another is the immune system. Once the animal is safe, the body comes back to balance.
The problem is with chronic stress. In humans it is the chronic social stress. The digestion is impaired, the immune system is impaired.
