Pain is an unpleasant feeling that is conveyed to the brain by sensory neurons. The discomfort signals actual or potential injury to the body.

However, pain is more than a sensation, or the physical awareness of pain; it also includes perception, the subjective interpretation of the discomfort.

Perception gives information on the pain’s location, intensity, and something about its nature. The various conscious and unconscious responses to both sensations and perception, including the emotional response, add further definition to the overall concept of pain.


Pain arises from any number of situations. Injury is a major cause, but pain may also arise from a wide variety of illnesses. It may accompany a psychological condition, such as depression, or may even occur in the absence of a recognizable trigger.

Acute pain

Acute pain often results from ordinary tissue damage, such as a skin burn or broken bone. Acute pain can also be associated with headaches or muscle cramps. This type of pain usually goes away as the injury heals or the cause of the pain (stimulus) is removed.

To understand acute pain, it is necessary to understand the nerves that support it. Nerve cells, or neurons, perform many functions in the body. Although their general purpose, providing an interface between the brain and the body, remains constant, their capabilities vary widely. Certain types of neurons are capable of transmitting a pain signal to the brain.

As a group, these pain-sensing neurons are called nociceptors, and virtually every surface and organ of the body is wired with them. The central part of these cells is located in the spine, and they send threadlike projections to every part of the body. Nociceptors are classified according to the stimulus that prompts them to transmit a pain signal.

Thermoreceptive nociceptors are stimulated by temperatures that are potentially tissue damaging. Mechanoreceptive nociceptors respond to a pressure stimulus that may cause injury.

Polymodal nociceptors are the most sensitive and can respond to temperature and pressure. Polymodal nociceptors also respond to chemicals released by the cells in the area from which the pain originates.

Nerve cell endings, or receptors, are at the front end of pain sensation. A stimulus at this part of the nociceptor unleashes a cascade of neurotransmitters (chemicals that transmit information within the nervous system) in the spine. Each neurotransmitter has a purpose. For example, substance P relays the pain message to nerves leading to the spinal cord and brain.

These neurotransmitters may also stimulate nerves leading back to the site of the injury. This response prompts cells in the injured area to release chemicals that not only trigger an immune response, but also influence the intensity and duration of the pain.

Chronic and abnormal pain

Chronic pain refers to pain that persists after an acute injury heals, cancer pain, pain related to a persistent or degenerative disease, and long-term pain from an unidentifiable cause.

It is estimated that one in three people in the United States will experience chronic pain at some point in their lives. Of these people, approximately 50 million are either partially or completely disabled.

Chronic pain may be caused by the body’s response to acute pain. In the presence of continued stimulation of nociceptors, changes occur within the nervous system. Changes at the molecular level are dramatic and may include alterations in genetic transcription of neurotransmitters and receptors.

These changes may also occur in the absence of an identifiable cause; one of the frustrating aspects of chronic pain is that the stimulus may be unknown. For example, the stimulus cannot be identified in as many as 85% of individuals suffering lower back pain.

Other types of abnormal pain include allodynia, hyperalgesia, and phantom limb pain. These types of pain often arise from some damage to the nervous system (neuropathic). Allodynia refers to a feeling of pain in response to a normally harmless stimulus.

For example, some individuals who have suffered nerve damage as a result of viral infection experience unbearable pain from just the light weight of their clothing. Hyperalgesia is somewhat related to allodynia in that the response to a painful stimulus is extreme.

In this case, a mild pain stimulus, such as a pin prick, causes a maximum pain response. Phantom limb pain occurs after a limb is amputated; although an individual may be missing the limb, the nervous system continues to perceive pain originating from the area.

Causes and symptoms

Baby in pain
Baby in pain

Pain is the most common symptom of injury and disease, and descriptions can range in intensity from a mere ache to unbearable agony. Nociceptors have the ability to convey information to the brain that indicates the location, nature, and intensity of the pain.

For example, stepping on a nail sends an information-packed message to the brain: the foot has experienced a puncture wound that hurts a lot.

Pain perception also varies depending on the location of the pain. The kinds of stimuli that cause a pain response on the skin include pricking, cutting, crushing, burning, and freezing. These same stimuli would not generate much of a response in the intestine. Intestinal pain arises from stimuli such as swelling, inflammation, and distension.


Pain is considered in conjunction with other symptoms and individual experiences. An observable injury, such as a broken bone, may be a clear indicator of the type of pain a person is suffering.

Determining the specific cause of internal pain is more difficult. Other symptoms, such as fever or nausea, help narrow down the possibilities. In some cases, such as lower back pain, a specific cause may not be identifiable.

Diagnosis of the disease causing a specific pain is further complicated by the fact that pain can be referred to (felt at) a skin site that does not seem to be connected to the site of the pain’s origin. For example, pain arising from fluid accumulating at the base of the lung may be referred to the shoulder.

Since pain is a subjective experience, it may be very difficult to communicate its exact quality and intensity to other people. There are no diagnostic tests that can determine the quality or intensity of an individual’s pain.

Therefore, a medical examination will include a lot of questions about where the pain is located, its intensity, and its nature. Questions are also directed at what kinds of things increase or relieve the pain, how long it has lasted, and whether there are any variations in it. An individual may be asked to use a pain scale to describe the pain.

One such scale assigns a number to the pain intensity. For example, 0 may indicate no pain, and 10 may indicate the worst pain the person could imagine. Scales are modified for infants and children to accommodate their level of comprehension.


Both physical and psychological aspects of pain can be dealt with through alternative treatment. Some of the most popular treatment options include herbal therapies, nutritional therapies, homeopathy, acupressure and acupuncture, massage, chiropractic, guided imagery, and relaxation techniques, such as yoga, hypnosis, and meditation. Hydrotherapy can also be very beneficial for pain relief.

Herbal therapies

Mild natural painkillers are used as herbal remedies for pain. They should only be used for mild to moderate chronic pain. However, unlike prescription drugs, they are not addictive and do not dull the senses.

In addition, they can help heal the nervous system as well as relieving pain. The following herbal remedies have been known to provide pain relief:
  • Capsaisin: is found naturally in cayenne pepper. (Its cream or gel form may be able to relieve some arthritic pain.)
  • Bromelain: reduce inflammation.
  • Curcumin: reduces inflammation.
  • Kava kava: helps relax the body.
  • Pine-bark and grape-seed extracts: reduces inflammation.
  • Pain-relief tea: is composed of white willow bark, chamomile, skullcap, valerian root and licorice root. (This herbal preparation may be effective in relieving normal aches and pain. However, persons with high blood pressure or those allergic to aspirin should avoid using this preparation.)
Nutritional therapy

Diet and nutrition can play important roles in controlling chronic pain. Patients with chronic pain some times find relief just by eating healthy foods and by adding nutritional supplements with pain-killing properties. A diet high in fiber and complex carbohydrates is recommended.

Because inflammation is often caused by allergic reactions, patients should eliminate allergic foods from their diets. They should also avoid foods high in fats or margarine, red meat, dairy products, shell-fish, alcohol, and coffee.

In addition, they may consider taking one of the following nutritional supplements: flaxseed oil, bromelain, calcium taken with magnesium, vitamin C taken with bioflavonoids, and glucosamine.

Glucosamine sulfate is one of the best natural remedies available for arthritic pain. Studies have shown that it effectively reduces pain and improves joint movement in 80% of arthritic patients. It works by healing and regenerating new connective tissues damaged by the inflammatory process.

It may also increase the level of endorphins, the body’s natural painkillers, and reduces inflammation in most arthritic patients. Recently, researchers also confirmed what thousands of people with arthritis have known for a long time — that cod liver oil eases the pain of arthritis.

A new study says that the omega-3 fatty acids in cod liver oil break down joint cartilage, slowing destruction of the joints and easing pain. This has been good news for arthritis sufferers who can not tolerate the prescription drugs available for arthritis treatment.


Depending on a patient’s specific condition, a homeopathic physician may prescribe one of the following medications for pain management:
  • Arnica: for treatment of acute pain after an injury.
  • Hypericum: for treatment of pain in nerves, fingers or toes after injury or surgery.
  • Ledum: for treatment of pain associated with black-and-blue bruises and puncture wounds.

Acupuncture involves inserting needles at various points on the skin of the body. These needles direct chi (life force) to organs or functions of the body.

This therapy possibly works by triggering the release of endorphins, therefore dulling the perception of pain. Acupuncture can effectively reduce most chronic pain. However, it may require up to 10 sessions before results are noticeable.

A 2002 study showed that acupuncture worked well for chronic neck pain and range of motion, but that its long-term effects were limited. It is important that patients request disposable needles to prevent transmission of AIDS, hepatitis, and other infectious diseases.


There are some acupressure techniques that patients can train themselves to do to help relieve pain. Using thumbs or fingers to apply pressure at appropriate acupressure points in the body, a person can release muscular tension in the head, neck or shoulder; calm the nervous system and relieve painful symptoms. Like acupuncture, acupressure probably works by releasing endorphins.


Massage involves using physical manipulation techniques to make various parts of the body, such as muscles, connective tissues, and vertebrae, work together and function properly. This form of therapy may effectively reduce stress and physical pain.


Chiropractors treat patients by manipulating joints and the spine. It is believed that pain, especially back pain, is caused by misalignment of the spine. This form of treatment is most effective in patients with persistent back pain and neck problems. It is also effective in patients with acute, uncomplicated low back pain.

Relaxation therapy

Relaxation techniques include meditation, yoga, guided imagery, biofeedback, and hypnotherapy. When practiced regularly, these techniques have been shown to relax muscles and reduce tension and stress-related pain.

Lifestyle changes

Lifestyles can be changed to include a healthier diet and regular exercise. Regular exercise, aside from relieving stress, has been shown to increase endorphins.


This form of therapy uses hot and cold compresses, whirlpools, saunas, and alternating cold/warm showers or body wraps to reduce the soreness of aching joints, inflamed muscles, chronic muscle strains, and backache. Some of these treatments can be done at home.

Allopathic treatment

There are many drugs aimed at preventing or treating pain. Nonopioid analgesics, narcotic analgesics, corticosteroids, anticonvulsant drugs, and tricyclic antidepressants work by blocking the production, release, or uptake of neurotransmitters.

Nonopioid analgesics are used for treatment of minor pain. They include common over-the-counter medications such as aspirin, acetaminophen (Tylenol), and ibuprofen (Advil).

Narcotic analgesics such as codeine, morphine, and methadone are used for more severe pain, such as cancer pain. These medications are available with a doctor’s prescription.

Initially developed to treat seizures and depression, some anticonvulsants and antidepressants now also have pain-killing applications. Finally, corticosteroid injections directly into or near the nerve that is transmitting the pain signal are reserved for intractable (unrelenting) pain that is not treatable by other medications.

Drugs are not always effective in controlling pain. Surgical methods are used as a last resort if drugs and local anesthetics fail. Electrode implants are the least destructive surgical procedure.

However, this method may not completely control pain and is not used frequently. Other surgical techniques involve destroying or severing the nerve, but the use of this technique is limited by side effects, including unpleasant numbness.

Expected results

Successful pain treatment is highly dependent on successful resolution of the pain’s cause. Acute pain will stop when an injury heals or when an underlying problem is treated successfully. Chronic pain and abnormal pain are more difficult to treat, and it may take longer to find a successful resolution. Some pain is intractable and will require extreme measures for relief.

In 2002, several health care organizations got together to form a panel charged with working on standards for evaluating effectiveness of pain management for patients who suffer from cancer, arthritis, and back pain. The standards will help physicians and others better measure patients’ pain and effectiveness of pain management drugs and techniques.


Pain is generally preventable only to the degree that the cause of the pain is preventable; diseases and injuries are often unavoidable. However, increased pain, pain from surgery and other medical procedures, and continuing pain are preventable through drug treatments and alternative therapies.

For many years, experts thought that arthritis patients should not exercise because it would damage their joints. However, a 2002 report said that regular low-impact exercise such as water aerobics or riding a stationary bicycle can actually help arthritic patients prevent pain.