Stress is a complex concept that has both mental and physiological components. Though most forms of stress are psychological, they trigger a variety of physiological changes. These changes include ones in the immune function, indicating a link between the stress and immune system.Stress-related cases have grown phenomenally over the last couple of decades. Psychiatrists believe that the growth has been about a thousand times in the last ten years. Medically, stress is defined as a perturbation of the body’s internal equilibrium.