Why rub a bump...

January 3, 2006 3:45 PM

If you've just bumped into something quite hard, why does it seem to help if you rub the area very hard...

...wherever it is on your body.

I've always found that even though the pain can be intense while you're rubbing the area, it is much less later on compared to having just left the area alone. Also, there is no bruising which I find there would be if you didn't rub.

So...why rub?

posted by mikeanegus to Health & Fitness (10 answers total)

No one really knows, but for speculation try googling "the gateway theory of pain".
posted by jeb at 4:03 PM on January 3, 2006

i thought it was because the pain and touch receptors cant be active at the same time, probably the gateway theory
posted by GleepGlop at 4:12 PM on January 3, 2006

I'd've guessed that stimulation of blood flow to the area was the aim.
posted by pompomtom at 4:21 PM on January 3, 2006

I figure it reduces the blood flow to minimize internal bleeding.
But it really does work well.
posted by weapons-grade pandemonium at 4:41 PM on January 3, 2006

Actually, I find that if I bump into something quite hard, while there isn't a bruise initially, one tends to develop, but that may be because I tend to bruise easily.

I rub the area and while the bruise turns different shades of black and blue for the first day or two, it eventually fades away--oftentimes sooner than if I hadn't rubbed it. So yeah, I think it has to do with the stimulation of blood flow.
posted by phoenixc at 4:46 PM on January 3, 2006

I always thought it was due to the body releasing endorphins, but I may be wrong.
posted by borkencode at 4:47 PM on January 3, 2006

borkencode/ by giving it more pain, the endorphins would help? Maybe...

My grandmother always told me that it's to dissuade bruising.
posted by Sallysings at 5:26 PM on January 3, 2006

I second borkencode: when you rub your skin the body releases endorphins for various reasons in order to encourage the rubbing.
posted by awesomebrad at 5:28 PM on January 3, 2006

Best answer: Pressure and heat generated by rubbing stimulates pressure and temperature receptors, and the resulting nerve impulses outnumber the pain impulses (generated by inflammation from the bump) and are either transmitted preferentially, or percieved more strongly by the brain than the pain sensation*.

This is my understanding of it, based on what I learnt in a lecture on pain and pain pathways given by a physician from the pain clinic of a major hospital. So, you know, blame them and not me if it's wrong :)

As for bruising, applying pressure to the area -- such as when you rub it -- reduces blood flow, so less will bleed from the damaged blood vessels to cause a bruise. Like when you get a blood test, and they ask you to hold that cotton wool on the puncture area for a minute.

* Whether it's transmitted preferentially, or percieved more strongly, I'm not sure. I should have listened more closely. The net effect is the same though.
posted by teem at 6:24 PM on January 3, 2006

Teem is right. "Deep touch," pain, and temperature, affectionately known as "the little three," travel in the same paths along the spinal cord and brainstem; the theory is that by activating the deep touch nerves, you cancel out some of the pain information.
posted by gramcracker at 10:40 PM on January 3, 2006