An unpleasant sensation often felt as a result of tissue disease or damage

  • Age, gender, genetics, and lifestyle are not significant factors

Pain is the body’s response to an injury or a disease that results in tissue damage. Pain usually functions as a protective warning mechanism that helps to prevent further damage, although chronic (long-term) pain often seems to serve no useful function. Everyone has experienced pain, but its type and severity depend to some extent on the cause. For example, pain that results from a sports injury may be less severe than that of a similar injury caused by a violent assault. Mood and personality also affect the way we perceive pain. For example, fear or anxiety can make pain worse, while relaxation may help to relieve it to a certain extent.

The brain and spinal cord produce their own painkillers, known as endorphins, in response to pain. Endorphins are natural chemicals that are closely related to morphine and act as highly effective pain relievers for short periods but are less effective for chronic pain.

Most forms of pain can now be controlled as a result of improvements in treatment, and it is rare for someone to have to live with persistent pain.

What are the causes?

When tissue is damaged by trauma, infection, or a problem with its blood supply, specialized nerve endings called pain receptors are stimulated. Electrical signals travel along the nerves and through the spinal cord to the brain, which interprets them as pain. While this is happening, the damaged tissues release chemicals known as prostaglandins, which cause inflammation and swelling. The prostaglandins further stimulate the pain receptors. The skin and other sensitive parts of the body, such as the tongue and the eyes, have a large number of pain receptors and are therefore very sensitive to painful stimuli. The internal organs of the body have fewer pain receptors and are insensitive to most types of injury.

What are the types?

Although each individual may describe the character or the site of pain in a different way, there are some types of pain that usually result from specific problems. For example, throbbing pain is often due to increased blood flow, either as a result of widening of the blood vessels, as may occur in migraine, or because of an increase in blood flow through injured tissues. Severe, shooting pains, such as sciatica, can be caused by pressure or irritation of the nerve at the point where it emerges from the spinal cord. Colicky pain is caused by intermittent stretching and contraction of muscles in the walls of the intestines, or in other parts of the body such as the bile ducts, which lead from the liver to the intestine.

The location of the pain usually acts as a good guide to its source. However, in some cases, overlapping nerve pathways can result in a confused message, causing pain to be felt in a different area of the body from the site where it originates. This type of pain, known as referred pain, occurs when the nerves carrying the sensation of pain merge with other nerves before they reach the brain. For example, hip problems may be felt as knee pain, while problems with a tooth may be felt as earache. Heart problems can cause pain across the chest, into the neck, and in one or both arms. Pain due to problems in the intestines tends to be felt in the centre of the abdomen and is felt locally only when the abdominal wall is affected, as in the late stages of appendicitis.

Sudden (acute), severe pain may be associated with other symptoms, such as pale skin, sweating, nausea or vomiting, rapid pulse, and dilated pupils, and may even result in fainting. Prolonged periods of severe pain that continue for weeks or months may lead to depression, loss of weight as a result of decreased appetite, and disturbed sleep (see Insomnia).

What might be done?

If you experience severe or recurrent unexplained pain you should see your doctor, who may be able to establish the cause of pain after a physical examination. Further investigations, including blood tests and imaging tests such as ultrasound scanning, may be necessary if there is no obvious cause.

Since it is difficult to measure the severity of pain, your doctor may ask how the pain affects your sleep and your ability to cope with daily activities. You may also be asked to describe the severity of the pain on a scale of 1 to 10, using 1 for slight discomfort and 10 for almost unbearable pain.

The most effective remedy for pain is treatment of the underlying cause, if possible. However, pain relief is also important until treatment of the cause takes effect. There are many different ways to relieve pain, including drugs and physical methods. The form of pain relief chosen depends on the cause and type of pain you experience.

Since pain, especially persistent pain, is influenced by other factors, such as personality and levels of stress, treatment has to be tailored to the individual.

Drug treatment

Virtually all short-lived pain and much long-term pain can be relieved by painkillers. When pain is caused partly by local prostaglandin release, treatment with a nonsteroidal anti-inflammatory drug such as ibuprofen often works well because these drugs limit the release of prostaglandins.

Opioid drugs, such as morphine and codeine, act directly on the part of the brain that perceives pain and are usually highly effective. Opioid drugs may be needed to relieve intense pain, such as that following surgery, and the severe pain associated with some cancers (see Pain relief for cancer). The risk of addiction to these drugs is small when they are used for short periods, and dependence is not a cause for concern when they are used in caring for a terminally ill person.

In addition to painkillers, a number of other drugs are prescribed for certain types of pain. These include local anaesthetics and drugs that affect the transmission of nerve impulses, such as antidepressant drugs and anticonvulsant drugs. Pain that is caused by muscle tension may be relieved by small doses of antidepressants. Anticonvulsant drugs are often used to treat pain associated with neuropathies, such as trigeminal neuralgia.

Physical treatment

A wide range of nondrug therapies is available to help to relieve pain, including gentle massage and the use of hot or cold compresses. These treatments both alter blood flow through damaged tissues and stimulate other nerve endings, blocking pain.

Acupuncture may be helpful for some types of pain and may be used to relieve pain after operations or for persistent pain that does not respond to other types of treatment.

If your pain is due to damaged ligaments or muscles, your doctor may offer ultrasound treatment, in which sound waves produce vibrations in the tissues and generate heat. Transcutaneous electrical nerve stimulation (see Pain relief using TENS) uses electric impulses to reduce pain and is sometimes used for lower back pain or during labour.

Nerve endings

Branching nerve endings, as shown here, may respond to tissue damage by sending electrical signals to the brain. These signals are then interpreted as pain.

What is the prognosis?

Almost all pain can be relieved to some degree, even if the underlying cause of the pain cannot be definitively treated. However, persistent pain is often more difficult to control than acute pain.

Treatment: Pain Relief Using TENS


Tension Headaches


Cluster Headaches

Chronic Fatigue Syndrome

From the 2010 revision of the Complete Home Medical Guide © Dorling Kindersley Limited.

The subjects, conditions and treatments covered in this encyclopaedia are for information only and may not be covered by your insurance product should you make a claim.

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