OK, we’ve always heard that you should always wear some sort of head covering when it’s cold out since “50% of our body heat lost is through our head”.
I remember hearing somewhere that the study that originally provided the 50% number was an old (1950s era) military study that was based on erroneous data, and that the real number was nowhere near that.
A Google search turns up many absolute citations of 30%, 40% and 50%, and this one: http://www.msu.edu/user/manns/myths.html (myth #18) seems to at least partially confirm the “50% is BS” theory. None of these sites, however, cite any sort of actual study, just a blind allegiance to whichever number they picked out of the sky.
So anyhoo, does anyone know of a study done by a reputable source, and if so, can you provide a citation?
Don’t know why this is bugging me so much, but I read someone in a scuba newsgroup toeing the “50% heat loss” party line and I’d like to know for sure. Or as sure as I can get…
No scientific answer here, but anecdotally, I stopped being miserable waiting for buses in the Chicago winter when I learned to wear a hat. It seems to have the effect (for me) of just making me feel warmer in general, and not just the top of my head.
I remember reading that the “If your feet are cold, put on a hat” theorem was being challenged by somebody. The original idea was that not only a lot of heat was radiated by your bare head, but that the body’s “thermostat” was located in the back of the head and neck.
While there may be contrary information out there somewhere, I continue to put on a hat when my enormous feet are cold. I hate having cold ears.
Again, no scientific answer here, but worth considering is that the head, notably including the brain, has a considerable blood supply; in cold conditions, blood vessels in other parts of the body constrict to reduce flow and conserve heat; the brain doesn’t - it keeps on going (the alternative would be loss of consciousness).
On top of that, the head is also relatively poorly insulated. Between the brain and the atmosphere, there’s a few membranes and a thin layer of bone and skin, but no thick layer of fat or significant muscle like on the rest of the body.
Fortunately, there’s a lot of hair, but many people have cut most of it away (or it’s fallen out due to age). Short hair isn’t a great insulator when it’s windy, and if hair gets wet it’ll act as a big heat sink, thieving energy from your head.
Preliminary conclusion: Your brain is a haemodynamic monster and it is chewing up a proportionally gigantic amount of your bodies resources. That said, (and on preview, contrary to wolfstu’s post), your skin, galea aponurotica, bone, epidural space, superior sagittal sinus, dura matter, subdural space, arachnoid, subarachnoid space, and pia mater actually provide pretty good insulation (those come not from my brain but a post of “The Brain” on my wall showing everything that comes between cortex and air).
Not sure what to say about the “human thermal plume,” but intuitively, heat rises, and if the plume is going upwards it makes sense that it’s going to take some from the top of your head with it.
Surely the % will depend on how well insulated the rest of your body is, otherwise the 50% claim would imply that you would be just as warm standing at the bus stop naked except for a fur lined hat as you would be well clothed but bare headed, which sounds absurd to me. That being the case all quoted % figures are questionable as they all make assumptions about your other clothing.
The rate of heat transfer between two substance is determined by the difference in temperature between them. So all else being equal, a warmer body loses heat faster than a cooler body.
Surprisingly, there doesn’t seem to be a lot of thermal imaging porn on the internet yet. I mean, they have midget clown porn, but no infrared nudie pics? How am I supposed to… ah… do research?
As for the “Completely naked except for a furry hat!” comment… you’d be surprised.
