Pain is a feeling set off in the nervous system. Acute pain lets you know that you may be injured or have a problem you need to take care of. Chronic pain is different. The pain signals go on for weeks, months, or even years. The original cause may have been an injury or infection. There may be an ongoing cause of pain, such as arthritis or cancer. But in some cases there is no clear cause.
Click here for more information. http://www.nlm.nih.gov/medlineplus/chronicpain.html