Pain can be caused by many injuries, conditions and diseases. Pain may also be caused by infection. For example, encephalitis (abnormal swelling or inflammation of the brain) is usually caused by viral infection.

Acute pain is most often caused by disease, infection, inflammation or trauma to tissues and is usually easy to diagnose. Causes of acute pain include:

• Injuries. These include sprains, strains, bruises, tears, dislocations and fractures. These commonly occur while playing sports, at home, in the workplace or while driving. Some people who have had a spinal cord injury develop a condition called central pain syndrome. They can experience intense pain ranging from tingling to burning.

• Burns. Depending on the injury, pain caused by burns can be excruciating. Patients can still experience pain at the location of the burn even after it has healed.
  
  
• Infection. Invasion of the body by a pathogen such as a virus, bacterium or fungus. Infections are often the cause of acute inflammatory conditions such as appendicitis. Some infectious diseases, including Lyme disease and meningitis, can cause chronic problems.
  
  
• Surgery. Control of pain associated with surgery includes presurgical preparation and monitoring of the patient before, during and after the procedure.

The cause of chronic pain is not always evident. It can result from an acute condition that has not resolved within the expected recovery time, such as a fracture that has not healed properly or a wound that has become infected. However, in many cases it is caused by degenerative, rheumatic or autoimmune conditions, such as:

• Arthritis. Millions of Americans have arthritic conditions such as osteoarthritis, rheumatoid arthritis, ankylosing spondylitis and gout. These conditions are characterized by pain in joints and sometimes other parts of the body, such as the skin or eyes.

• Repetitive stress injuries. Conditions that result from repeated motions performed during work or other activities. Some examples are tendinitis, bursitis and tennis elbow. Carpal tunnel syndrome has long been though to be due at least partly to repetitive strain, but recent research implicates genetics and other factors.
  
  
• Fibromyalgia. A chronic pain illness characterized by musculoskeletal aches, pain and stiffness, soft tissue tenderness, general fatigue and sleep disturbances. 
  
  
• Myofascial pain syndrome. A condition characterized by chronic pain in the muscle tissues.
  
  
• Chronic fatigue syndrome. A disorder marked by exhaustion, pain and other symptoms.
  
  
• Systemic lupus erythematosus. An autoimmune disease that can affect many parts of the body, including the skin, joints and kidneys.