I cut the inside of my finger on a piece of smooth metal foil, but felt nothing. The first I realised I had done it was when I started leaving patches of blood on things. The cut was quite deep and took a while to staunch, so why was it completely painless? I’ve had similar cuts on sharp objects before and mostly they’ve been very painful, but every so often some cuts don’t seem to hurt at all.
• I’m an anaesthetist, and I “cut” my patients’ hands every day when I insert an , usually into the back of their hand or wrist. Patients expect it to hurt, as do I, so I warn them. Sometimes afterwards the patient will ask if I have done it yet, and exclaim that I must be good, as it didn’t hurt a bit.
I accept this praise modestly, because I know skin sensation is perceived via discrete receptors with free nerve endings used for detecting pain. If I choose an area that happens not to contain pain receptors, the patient may feel the needle pressure but no pain.
Advertisement
John Davies, Consultant Anaesthetist, Lancaster, UK
• It depends on how cleanly the nerves are severed. For example, the edges of the tins and lids left by a tin opener are rougher than those of metal foil, and tear the nerve endings. It is this tearing of the pain receptors that also makes paper cuts so sore, because the edges of even the shiniest paper are rough at the microscopic scale. Any contamination of the wound with acidic or salty liquid from the tin contents, or with microscopic debris lodged in the offending edge or on the skin, will further irritate the nerves.
“Tearing of pain receptors makes paper cuts so sore – even shiny paper is rough at the microscopic scale”
Another factor is the number and density of pain receptors on the part of the skin that is cut. Fingers have a very high density of nerve endings, including those for touch and temperature, but even across a given finger tip these are not uniformly distributed. An otherwise identical cut will be more painful if it occurs at a spot where they are more densely packed and more endings get damaged.
There is a circadian – or daily – rhythm in pain threshold. Generally, the least pain is experienced in early to mid-afternoon, with more experienced in the morning and at bedtime. Individuals differ in their tolerance of pain, and there is evidence that people adopt similar coping mechanisms to their parents.
Other factors can also influence someone’s perceived pain at a given time, through complex interactions between chemical neurotransmitters, hormones and the way in which nerves are hard-wired. Inspecting or applying pressure to the injury, good health and physical fitness, and being immersed in an activity help reduce pain. Negative moods and sleep deprivation, in contrast, tend to worsen it.
About a year ago I had carpal tunnel surgery on my hand, which involved dividing and parting the overlying tissues to access the carpal ligament where the palm joins the wrist. Having expected discomfort as the anaesthetic wore off, I was surprised by the absence of pain. The procedure was carried out by a top surgeon using finest grade instruments. I was even advised to return to my passion for piano quickly to maintain motility of the tendons, and I know at least one person who, after carpal tunnel release on both hands, was back at work the next day.
Len Winokur, Leeds, UK