Stress is often described as a feeling of being overwhelmed, worried or run-down. Stress can affect people of all ages, genders and circumstances and can lead to both physical and psychological health issues. By definition, stress is any uncomfortable "emotional experience accompanied by predictable biochemical, physiological and behavioral changes." Some stress can be beneficial at times, producing a boost that provides the drive and energy to help people get through situations like exams or work deadlines. However, an extreme amount of stress can have health consequences and adversely affect the immune, cardiovascular, neuroendocrine and central nervous systems.