Wonk! Rub, Rub, Rub...

I’m stepping off the bus the other day and, once again, bump the doorframe with my forehead.

I shrug it off for 30 seconds or so, with my best cat-like “I meant to do that expression” and finally resort to rubbing it a few times to get it to stop hurting. It does.

The question is, therefore, why does rubbing something make it stop hurting?

It increases circulation, moving damaged cells away from the injury site and moving fresh blood and other fluids to the site. This is most useful in places like the forehead, shins, elbow, etc. where circulation is minimal.

Trinopus

I’m not convinced that rubbing the spot where you bonked your head will make it stop hurting sooner. I think it’s merely an automatic reaction. Try this: get a stopwatch, bonk your head, rub and time to see how long it takes for the pain to diminish. Bonk your head again, in a slightly different spot, time how long it takes the pain to diminish without rubbing. Repeat for several trials. :slight_smile:

Some types of pain, such as muscular soreness resulting from fatigue, do diminish faster with rubbing the affected area since it helps releases the lactic acid, which is the cause of the soreness.
So there is a reason we have this automatic reaction to pain, it just doesn’t apply in all cases.

I spent about 1 minute looking on google for a cite, but I couldn’t find one. I’ll look later just to be sure.

I’ve understood rubbing to help because the nerves can carry only a limited amount of information. In other words, it is a bandwidth issue. Rubbing fills some of the bandwidth with something other than “pain”.

I heard this suggestion also, I think it was called the “Gateway Hypothesis” suggesting that the spinal cord acts as a gate that only allows a certain amount of information through it.

I’m sure that there is a limit to the amount of sensory input you can process at once. That’s why a certain amount of pain will make your pass out. I don’t see most bumps on the head to get close to that threshold though so I don’t buy the theory that rubbing helps unless it causes enough sensory overload to make you faint.

I think rather than blocking the pain stimuli by over loading the pathways, that rubbing works by distracting you from concentrating on the pain. This is just my hypothesis. A test would be to next time you bang your head, try rubbing your elbow instead, and see if that helps.

Medical school answer; I have no cite other than lecture materials, but if anyone is so inclined I may be able to conjure a study of some sort.

Pain sensation is carried on a nerve type called a C-fiber. Tactile sensation is carried on A-fibers. The Gateway Hypothesis hypothesizes that there is a feedback loop in the spinal column from the A-fibers to the C-fibers. So rubbing the injured area increases the tactile nerve stimulation which in turn negatively feedbacks on the pain fibers decreasing the intensity of the pain. It wouldn’t decrease the duration of the pain per se though.

Rubbing a separate area wouldn’t work because there is no feedback loop between the elbow A-fibers and the forehead C-fibers