The human body responds to stress with a powerful fight-or-flight reaction. Hormone surge through the body, causing the heart to pump faster and sending extra supplies of energy into the bloodstream. For much of human history, this emergency response system was useful: It enabled people to survive immediate physical threats, like an attack from a wild animal. But today, the stress in most people's lives comes from the more psychological and seemingly endless pressures of modern life. Daily challenges like a long commute or a difficult boss can turn on the stress hormones -- and because these conditions don't go away, the hormones don't shut off. Instead of helping you survive, this kind of stress response can actually make you sick.
Chronic stress can harm the body in several ways. The stress hormone cortisol, for instance, has been linked to an increase in fat around organs, known as visceral fat. The accumulation of visceral fat is dangerous, since these fat cells actively secrete hormones that can disrupt the functioning of the liver, pancreas and brain, causing problems such as insulin resistance, inflammation and metabolic syndrome. Chronic exposure to other stress hormones can also weaken the immune system and even change the structure of chromosomes.