Stress is what you feel when you have to handle more than you are used to. When you are stressed, your body responds as though you are in danger. It makes hormones that speed up your heart, make you breathe faster, and give you a burst of energy. This is called the fight-or-flight stress response.

Some stress is normal and even useful. Stress can help if you need to work hard or react quickly. For example, it can help you win a race or finish an important job on time.
 
But if stress happens too often or lasts too long, it can have bad effects. It can be linked to headaches, an upset stomach, back pain, and trouble sleeping. It can weaken your immune system, making it harder to fight off disease. If you already have a health problem, stress may make it worse. It can make you moody, tense, or depressed. Your relationships may suffer, and you may not do well at work or school.

WebMD. (2009, April 22). Retrieved from http://www.webmd.com/balance/stress-management/stress-management-topic-overview