Acute and Chronic pain

Pain can be described as Acute and Chronic, depending on its duration. Acute pain is of short duration and normally resolves when the body heals itself, for instance after injuries or operations.  Pain can become chronic or long-lasting, this may persist after the body has healed so is often not a useful sensation.

Acute pain is your body's way of saying that something is or might become damaging to you. Acute pain is generally sudden in onset, and lasts a relatively short time. It is often a warning sign so for example if you turn on a tap and put your hands under it, and the water that comes out is painfully hot, you will immediately pull your hands away. The pain warned you that if you continued to keep your hands in the water, they would probably get badly burned. As another example, your shoe may rub against your foot, causing you pain but no injury. If you ignore this warning sign, you can end up with a blister - damaged tissue - as well as pain. Acute pain generally disappears when the injury heals or the illness goes away (either of its own accord, or after successful treatment), or the body can no longer detect the source of the pain (for example, your rubbing shoe).

We know that damaged tissue for example from an injury does not always lead to pain, and the amount of pain doesn't always correspond to the amount of injury (so a paper cut can be very painful, and sometimes people don't notice that they've had a serious injury). This is because the danger sensors in the skin and soft tissues  (nociceptors) send messages to your spine which are then relayed to your head - your brain decides on the basis of other sensation, stress level, knowledge and previous experience whether those signals are dangerous and should be painful, or not.

Sometimes pain can become chronic, or persistent. It is said to be chronic when it is present to at least some degree for long periods of time (typically after 3-6 months).  Chronic pain may remain constant, or it can come and go, like the pain of migraines. It sometimes indicates a long-lasting health problem, which may or may not be serious and may or may not be treatable.  Chronic pain may be due to causes such as wear and tear of joints: this is called nociceptive pain.  Sometimes changes in the nervous system can themselves lead to pain: this is called neuropathic pain.  Indeed, sometimes pain itself can cause changes in the nervous system that lead to an increase in and maintenance of pain sensation (sometimes called 'sensitization' or 'pain wind-up').  Persistent pain can prevent the completion of daily tasks or certain movements and impacts upon all aspects of life including for example ability to concentrate, sleep, lowering ones mood, and decreasing social contact.

One way to understand pain sensitization is in terms of your home burglar alarm: normally the burglar alarm goes off loudly alerting you that someone is breaking into your house; but if a spider chooses to make its web over a detector then insignificant movements by that spider may be interpreted by the burglar alarm as being danger signals thus setting off the alarm. When someone has a nervous system sensitized to pain (the burglar alarm above) then sensations that would normally be interpreted as being harmless are interpreted by their brain as dangerous thus triggering a pain signal. An example of sensitization is having a hot shower when you have a sunburnt neck - normally this would be a nice hot shower, but the sunburn means that the sensation of hot water on your neck is felt as painful so you turn down the temperature and have a tepid shower. Some persistent pain conditions (for example fibromyalgia) seem to be partially due to the central nervous system (the brain and spinal cord) being sensitized to overreact to small danger signals (nociception) from the body, sensations that wouldn't normally cause pain. 

A strange feature of chronic (persistent) pain is that it may persist even after the injury that caused it has healed. So when you see a doctor in Pain clinic they will check you carefully to see if there are any treatable causes of your pain or other painkillers that could be tried. If your pain persists despite these treatments the doctor may refer you for pain management advice as we know that pain tends to affect us in various ways. For example, pain tends to restrict our movements (thus over time soft tissues shrink and movement becomes more painful and difficult), pain also tends to lower ones mood and often makes us withdraw socially. Pain management aims to keep you active, to keep you doing fun things and to promote social contact and thus challenge the downward spiral that may come with chronic pain.