Virtually every one of us feels pain, perhaps some more than others, but what is it, what causes it and why do different people react differently to it?

Simply, pain is a result of a stimulus to our nerves, which conduct an electrical impulse to our brain. The receptors in our skin and organs, responsible for picking up painful stimuli are called nociceptors and are specific to different types of pain, such as cutting, pricking, temperature or pressure. The signals are electrical impulses, which are set along the nerve fibres at approximately 200 miles per hour. When the brain receives and interprets the signals, it then sends out messages to the appropriate part(s) of the body, for example to move the hand away from the heat source. Effectively pain is a signal to STOP so that further damage can be avoided.

It is at this stage that psychological effects are felt. For example, with the first incidence of pain, a person could start to feel anxious, stressed or even fearful. If the pain is not removed the response can build to a stage where the individual can suffer poor sleep, decreased appetite, and there may be a feeling of helplessness. In turn this results in a lower pain threshold, causing the original pain stimulus to result in increased perception of pain. This cycle is often referred to as the vicious circle of pain (see attached diagram Vicious circle of pain (1)) and it is for this reason that pain relief is recommended by health care professionals.

Defining and describing pain
With over 1,300 nerve endings per square inch in our hands and 100 billion neurons in the brain, it is not surprising we all feel pain to some extent. The difficulty comes when trying to define pain. Given that pain is in part a psychological sensation, every individual's reaction to pain varies.

There are two main ways a health care professional will describe pain:

• Acute, which is a short-term pain. The pain is often severe and generally occurs when the body is trying to warn you of an injury, e.g. burn, sprained ankle or toothache.
• Chronic, which is long term pain. This pain occurs everyday and can be caused by conditions such as arthritis and back pain.

In addition to this there are many everyday words that are used to describe pain - throbbing, dull, deep (chronic pain) or stabbing, sharp, burning, sore (acute pain). In fact the McGill pain questionnaire, which was designed to help measure patients' subjective pain experience, uses over 87 words. Pain is without doubt one of the most individual of sensations.

Notes for editors
References:
(1) E-mail correspondence with Dr Chudler 11-04-2000

For further information please contact:

Karen Kelshaw
Consumer Health Information Centre
tel: 020 7421 9314
fax: 020 7421 9317
email: karen.kelshaw@pagb.co.uk

Pam Prentice
Doctor Patient Partnership
tel: 020 7383 6144
out of office hours: 0780 3399826
email: pprentice@bma.org.uk

Marianne Smith
Doctor Patient Partnership
tel 020 7383 6828
fax: 020 7383 6966
email: msmith@bma.org.u