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In praise of balaclavas: facial heat loss makes fingers cold

April 9th, 2011

Okay, this update isn’t exactly seasonal in the northern hemisphere — but winter will be back in another six months, so tuck this away for future reference. Researchers at the U.S. Army Research Institute of Environmental Medicine (Thermal and Mountain Medicine Division) did a neat little study in the European Journal of Applied Physiology looking at the effect of heat loss through the face.

Basically, 10 volunteers each spent two 60-minute sessions standing in a cold chamber (-15 C) facing into a 3 m/s wind (wind chill equivalent to -20 C). In one session, they wore a balaclava and goggles; in the other session, their face was bare (the balaclava was still on, but pulled down to expose the face, and the goggles were removed. Your face tries to stay as warm as possible, meaning that blood vessels there don’t constrict much even when it gets cold — so there’s the potential to lose large amounts of heat. In addition, there are some direct cues: for example, facial cold exposure triggers the trigeminal nerve, which causes blood vessels to extremities to constrict.

All of this means your fingers and toes are more likely to get cold. And that is, indeed, what they found:

finger temperature with balaclava

The other part of the test was that the subjects had to take their gloves off (while still wearing thin gloves) at multiple points during the test to perform dexterity tests (the Purdue Pegboard and the Minnesota Rate of Manipulation, for what it’s worth). Surprisingly, there were no differences between the trials. Apparently your hands get cold so quickly as soon as you take the mittens off that you no longer get any benefit from having been fractionally warmer a moment earlier.

So the takeaway here: if you get cold hands during winter exercise, keeping your face covered could make a difference. And there’s a bonus insight. Ever since I was a kid, I remember people saying things like “Wear a hat, because the body loses X percent of its heat through your head,” where X was always some enormous number like 90. I’ve always wondered what the actual numbers are. Here’s a passage from the introduction to this paper:

Froese and Burton (1957) provide an example of whole-body cold exposure (-4°C, 2.2 m/s wind) where about half of the resting heat production would be lost from a bare head if the rest of the body was well insulated (5 clo). They (Froese and Burton 1957) estimated that the addition of relatively little insulation (2.4 clo) on the head would restore heat balance, although a higher amount (3.5 clo) would be required if the face remained exposed to cold. If thermal face protection can restore heat balance, extremity cooling would also likely be limited.

So there you go. For that particular set of circumstances, about half of the heat your body produces is lost from the head (including the face). Of course, if you start moving, or if the rest of your body isn’t that warmly dressed, or if the temperature or wind conditions change, then the conclusions change. But still, 50% gives us a ballpark estimate. Neat.

And one final aside: the “standard amount of insulation required to keep a resting person warm in a windless room at 70 °F (21.1 °C) is equal to one ‘clo‘.”