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It's that time of year where I've started to hear it repeated that running cold water over your wrists is a way to rapidly cool down.

The theory goes that blood is close to the surface in this area so the constant flow of heat on one side and cold water on the other side will cause rapid cooling.

I had a cursory glance on Google Scholar but failed to find anything relevant, however, I did find this newspaper article, citing Dr Michael de Podesta at the National Physical Laboratory in Britain:

Another trick Flower suggests is running cold water over your wrists. ‘There are lots of little blood vessels on your wrist and these will keep the blood cool,’ he adds.

But it's not a very substantive source. Any ideas?

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  • Rapidly, compared to just sweating, I suppose.
    – user11643
    May 29, 2017 at 0:14
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    The wrists are so-called pulse points, points where larger than normal volumes of blood travel very close to the surface of the skin. The logic behind this is that cooling the wrists cools the blood, which in turn cools the body. It does seem a bit 19th century medicine / folklore tale.
    – David Hammen
    May 29, 2017 at 7:21
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    What would likely be good about that spot is that it's easy to access, not too intrusive to run water over, and would have pretty good blood-flow through it. I'd think running cool water all over your body or spreading out the contact would still be just as successful as trying to focus the cooling on one point. Heat transfer is proportional to area and thinness, so even if you have to go through thicker skin, the increase in area would probably have net advantage.
    – JMac
    May 29, 2017 at 12:01

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I have a hard time seeing how this can be very effective. You would need a high blood flow, and the arteries in the hands are not supplying very much. It is for me hard to find good averaged data, I can only find as part of some pathology, but still different google-fu answers on "blood flow through radial artery" show up as <50 ml/min. I did find this eventually, it is a mathematical model of blood flow which says the rate to hands through the radial artery is along the lines of 0.6 cm/s which makes 36ml/min. It is a truly minute amount of blood - it would take several days to pass your blood volume once through both radial arteries.

For me the main nail in this coffin is the fact that in addition to the minute amount, we know that exposure to cold induces vasoconstriction in the hands so the tiny trickle will become a negligible drop now and then if you cool your hands as well as your wrists ( - which is a reasonable assumed result of applying cold water near the radial artery)

You would be better off cooling down the big movers arteries and surface of the gut, the groin, the neck, the head - but I can see how that is an inconvenience. Those of us that inherited nothing from our fathers, not even hair - have it easier. Just submerge the scalp entirely, very recommended against heat.

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