Everyone has experienced pain at some time or other. A cut, a sports injury, childbirth, surgery, or kidney stones all can produce varying degrees of pain. In these cases, the pain has a known cause and resolves when the cause is no longer there. This type of pain is acute pain. Acute pain performs a function – it warns the body of a problem or injury.

Chronic pain, which is pain lasting months or recurring over years, is much different. The pain itself rarely continues to perform any useful function. Chronic pain can be quite disabling, often preventing people from working and enjoying life. It can lead to people feeling isolated, angry, frustrated, and guilty.

Many medical conditions or injuries can cause chronic pain. Some people will continue to experience pain long after recovering from an initial injury, such as a back injury. Other chronic pain is caused by chronic diseases such as arthritis or cancer, or by a lesion that does not heal. Some people have pain that does not have an identifiable cause. This is not to say that the pain is not real. Whatever the cause, chronic pain is real and should be treated.

The following conditions may be associated with chronic pain:

• cancer
• fibromyalgia
• spinal injury
• headaches
• back injury
• arthritis
• nerve inflammation or damage

Sometimes pain can be felt in a part of the body that is no longer there. This is called phantom limb pain, which develops as a result of amputation. When pain in one part of the body is felt in another part of the body, it is called referred pain.

The internal organs are not very responsive to pain; instead, pain in these areas may be felt more as a diffuse pain (i.e., pain spread over a large area), which is not easy to localize.

Acute pain results when a disease or injury sends a signal to special sensory nerve endings called nociceptors. Nociceptors are located in the skin, as well as in other structures including blood vessels and tendons. Pain signals travel from the nociceptors, through the sensory nerves, and up the spinal cord to the thalamus in the brain. The signal is then sent to the cerebral cortex, the part of the brain that processes thought.

On the way to the brain, natural body chemicals can change the pain signal. Substance P makes the pain signal stronger. Endorphins make it weaker. Pain is not actually felt until the message or signals get to the brain. Chronic pain can originate at many points in the above pathway.

In some cases, chronic pain may arise from injury to the nerves in our body. This type of pain is called neuropathic pain and is often the result of direct injury or disease of the nerves. Neuropathic pain is different from acute, nociceptive pain – people often complain of burning or radiating pain rather than dull, aching pain.

The cerebral cortex and the limbic system, which are the brain areas controlling emotion, process pain signals. How much pain is felt depends on a number of factors. Factors that increase how badly pain is felt include the following:

• previous bad experiences with pain
• insomnia
• anxiety
• depression

Anxiety can make pain much worse. Not knowing the cause of pain makes people anxious. The pain often seems less severe once they have a diagnosis of their medical condition. Worry about the seriousness of their condition can often also increase the severity of the pain.

Living with chronic pain can create a vicious cycle of anxiety, dependence on other people, and sleep deprivation. Chronic pain can make it unpleasant for people to live their daily life normally; it saps their energy and often negatively affects employment.

People suffering from chronic pain might stop social activities because of the pain. They might feel dependent on other people to help with daily tasks such as shopping. Sleeping can be difficult for someone who is in pain, or worried about being in pain. Constant pain and/or sleep deprivation can lead to depression or worsen existing mood disorders. Chronic pain may also cause a decrease in libido and appetite, as well as weight loss.

Pain that lasts 3 months or longer, or pain persisting over 1 month after an injury resolves is considered chronic pain.

Although it can be hard to describe pain exactly, your doctor needs to know how it feels and where it's coming from, what aggravates the pain, how it impacts your daily life, and what makes it better. Doctors often use pain scales to help rate the intensity of the pain and imaging tests to find out more about its possible causes.