How common is chronic pain?

More than 50 million Americans experience chronic pain that interferes with daily activities, according to the American Pain Foundation.

How does pain function?

Pain is a function of the nervous system, which is made up of nerve cells and fibers that send and receive messages in the form of electrical currents and chemical interactions.

The body may respond to messages that translate into pain in several ways. Nerve cells in the spinal cord may release chemicals that intensify pain, affecting the strength of the pain signal that reaches the brain. This is a process called wind-up or sensitization. The brain may block pain messages from traveling to higher parts of the brain or it may send nerve signals that release natural painkillers that diminish pain messages.

Other substances in the body cause the opposite reaction. A protein called substance P stimulates nerve endings at the site of the injury and spinal cord. This increases pain messages and worsens the pain sensation.

Do all people experience pain in the same way?

No. Sex and age appear to play a role. Research indicates that men and women respond differently to pain. Women are believed to seek aid more quickly, are more likely to use a variety of support resources to deal with pain and recover more quickly. The sex hormones estrogen (in women) and testosterone (in men) help account for the difference.

Then there's the gate control theory of pain, developed in the 1960s by psychologist Ronald Melzack and anatomist Patrick Wall. Under the theory, pain is "gated" or framed by past experience. Because of this, individuals who have undergone different experiences experience pain in different ways.