There are two types of pain, nociceptive pain and neuropathic pain. Nociceptive pain occurs when the peripheral nerve receptors that sense actual or potential tissue damage (nociceptors) are stimulated by an unpleasant sensation (noxious stimulus). Trauma and injury are common examples of noxious stimuli.

Nociceptive pain can be somatic or visceral. Somatic pain is usually constant and concentrated in one location of the body. It is sometimes described as sharp, aching, throbbing or gnawing. Visceral pain is usually not concentrated in one area and is often described as deep, aching or squeezing pain.

Neuropathic pain is caused by damage to the peripheral or central nervous system. It is often described as burning, electric, tingling or shooting.

Pain may also be described as acute or chronic. Acute pain is triggered by tissue damage from trauma, illness, injury or surgery. Acute pain may be mild or severe. It may pass quickly or last for months. Acute pain is usually localized to one area of the body, and its cause is usually easy to identify.

Chronic pain is long-term pain due to degenerative changes (e.g., osteoarthritis, degenerative disc disease), another chronic condition or pain that persists after the normal course of recovery of an illness or injury. It may remain constant or may come and go. The definition of some conditions includes a time frame, such as pain lasting at least three months for fibromyalgia or six months for chronic fatigue syndrome. Unlike acute pain, the cause of chronic pain is often difficult to diagnose. In some cases, chronic pain may occur without any indication of injury (e.g., fibromyalgia).

Pain can occur throughout the body:

• Headaches affect millions of people. The most common types of headaches include tension headaches (sometimes described as a tight band around the head) migraines (characterized by throbbing pain and other symptoms such as nausea) and cluster headaches (characterized by excruciating, piercing pain on one side of the head).
  
  
• Orofacial pain, dental pain, TMJ disorder, eye pain and ear pain are other types of head pain.
  
  
• Neck pain can result from trauma such as whiplash, improper posture and ergonomics or infectious diseases such as meningitis or encephalitis.

• Back pain is among the most common medical conditions in the United States and other developed nations. Its many causes include strain or sprain, sciatica, osteoporosis, scoliosis, pinched nerves, herniated disc, degenerative disc disease, spinal stenosis and ankylosing spondylitis.

• Shoulder pain often stems from osteoarthritis, tendinitis, bursitis, dislocation, separation, torn rotator cufftorn rotator cuff or frozen shoulder.
  
  
• Elbow, wrist and arm pain has many possible causes, including fractures, rheumatoid arthritis, carpal tunnel syndromecarpal tunnel syndrome, tennis elbow and golfer elbow.
  
  
• Chest pain can be due to many disorders ranging from heartburn to heart conditions to costochondritis to asthma to esophageal spasms.
  
  
• Abdominal pain can result from indigestion, ulcers, appendicitis, kidney stones or other problems involving internal organs.
  
  
• Pelvic pain includes sexual pain and testicular and scrotal pain.
  
  
• Leg pain, knee pain and foot pain have many possible causes including overuse, traumatic injury, gout and other types of arthritis, gait disturbances, diabetic neuropathy, complex regional pain syndrome and plantar fasciitis.
  
  
• Joint pain is not synonymous with arthritis. It can also be due to conditions including fibromyalgia, lupus, chronic fatigue syndrome, polymyalgia rheumatica, sarcoidosis, myofascial pain syndrome, sickle cell anemia and Lyme disease.