Cause

The cause of chronic pain is not clear. When you have an injury or illness, certain nerves send pain signals to your brain. With chronic pain, these pain signals continue for weeks, months, or even years after you recover. Chronic pain can develop after a major injury or illness, such as a back injury or shingles, or it can develop without a known cause. It is also possible that certain brain chemicals that usually suppress pain may not work properly.

Pain can affect:

• Muscles, bones, and joints. It also affects the ligaments and tendons. This pain can happen from injuries or muscle strain. Health problems like osteoarthritis, rheumatoid arthritis, and fibromyalgia also can cause it.
• Nerves and the nervous system. This type of pain happens because of pressure on nerves or damage to them from an injury or a health problem. Sometimes pain occurs when something goes wrong with the central nervous system. Diabetes, shingles, and sciatica are examples of health problems that cause nerve pain.
• Organs. Pain in your organs occurs because of injuries, infections, or health problems such as inflammatory bowel disease, irritable bowel syndrome, pelvic pain, and stomach ulcers.

You can have more than one kind of pain at the same time. For example, fibromyalgia can cause pain in muscles and nerves.