Pain is an unpleasant feeling that is conveyed to the brain by nerves in the body.


Pain arises from any number of situations. Injury is a major cause, but pain may also arise from an illness. It may accompany a psychological condition, such as depression, or may even occur in the absence of a recognizable trigger. 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 sensation and perception, including the emotional response, add further definition to the overall concept of pain.

Acute pain

Acute pain often results from 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 responsible for 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 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 experiences 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 medically identified in as many as 85 percent of individuals suffering from 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 pinprick, 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.


Pain is experienced by all age groups, both sexes, and all races and ethnic groups.

Causes and symptoms

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.

When to call the doctor

Parents should notify their physician or pediatrician if any of the following occurs:

  • The child is in severe pain.
  • The child has pain that lasts for more than three days.
  • Parents have questions or concerns about their child's treatment or condition.
  • The child is in the hospital and the parent thinks he or she is in pain. The sooner the pain is treated, the easier it is to control.


Pain is considered in view of 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 the possibilities. In some cases, such as lower back pain, a specific physiological cause may not be identified. 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 includes 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 has ever experienced. Scales are modified for infants and children to accommodate their level of comprehension.

A subsequent method of evaluating pain in children up to age four years was as of 2004 set to be implemented in 60 hospitals in the Netherlands. The Pain Observation Scale for Young Children, called POCIS, measures pain levels according to children's behavior in seven categories: facial expressions, crying, breathing, torso movements, movements in the arms and fingers and in the legs and toes, and restlessness. Physicians and nurses observe the intensity of these behaviors and calculate a pain severity score ranging from 0 to 7. Researchers from the University of Amsterdam who developed the scale said that existing behavioral pain measures were created for premature neonates or infants and may not be appropriate for older children. Some of those measures are upsetting for children because they require restraint or physical contact by a healthcare professional.

Alternative treatment

Both physical and psychological aspects of pain can be dealt with through alternative treatment. Some of the most popular treatment options include acupressure and acupuncture, massage, chiropractic, and relaxation techniques, such as yoga , hypnosis, and meditation. Herbal therapies are increasingly recognized as viable options; for example, capsaicin, the component that makes cayenne peppers spicy, is used in ointments to relieve the joint pain associated with arthritis. Contrast hydrotherapy can also be very beneficial for pain relief. Lifestyles can be changed to incorporate a healthier diet and regular exercise . Regular exercise, aside from relieving stress, has been shown to increase endorphins, painkillers naturally produced in the body.


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 requires extreme measures for relief.


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.

Parental concerns

If a child has a lot of pain, it is likely that more can be done to help. The first step is for parents to tell the child's doctor or nurse what their concerns are. They can ask what more can be done for the child to control pain. If parents are still concerned about their child's pain control, they can request a meeting with the doctor. Parents should list their concerns as clearly as possible. They should take a constructive approach and seek to form a partnership with the healthcare team in managing the child's pain. For parents who are still not satisfied with what is being done, some type of formal complaint to the hospital may be unavoidable. Pain management is the right of every child. Parents working with health providers are the best advocates for this right. The U.S. Department of Health and Human Services Agency for Health Care Policy and Research has developed guidelines for pain management. These guidelines establish a standard of care that should be followed. Parents can get a copy from the hospital library or directly from the government.


Acute pain —Pain in response to injury or another stimulus that resolves when the injury heals or the stimulus is removed.

Chronic pain —Pain that lasts over a prolonged period and threatens to disrupt daily life.

Neuron —The fundamental nerve cell of the nervous system.

Neurotransmitters —Chemicals in the brain that transmit nerve impulses.

Nociceptor —A nerve cell that is capable of sensing pain and transmitting a pain signal.

Referred pain —Pain that is experienced in one part of the body but originates in another organ or area. The pain is referred because the nerves that supply the damaged organ enter the spine in the same segment as the nerves that supply the area where the pain is felt.

Stimulus —Anything capable of eliciting a response in an organism or a part of that organism.



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American Chronic Pain Association. PO Box 850, Rocklin, CA 95677. Web site:

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Julia Barrett
Ken R. Wells

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