Stress is your body’s response to a demanding situation. Your brain causes hormones to flood your system. These increase your heart rate, regulate your blood pressure, expand or constrict the capacity of your lungs, and tense your muscles. Before you are fully aware of what is happening, your body is primed for action. When a stressful episode is over, your body comes off “high alert” and returns to normal.

Stress is a natural response that enables you to deal with challenging or dangerous situations. The stress response begins in your brain. Beneficial stress enables you to act or react quickly. A certain amount of stress can also help you to reach your goals or to perform better, perhaps during an exam, a job interview, or a sporting event.

However, prolonged, extreme, or chronic stress can harm you. When your body is repeatedly or constantly on “high alert,” you may begin to suffer physically, emotionally, and mentally. Your behavior, including the way you treat others, may change. Chronic stress can also lead to substance abuse and other unhealthy means of coping. It may even spiral into depression, burnout, or thoughts of suicide.

While stress may not affect everyone in the same way, it can contribute to a wide range of diseases. And it can affect nearly every part of the body.