There is widespread misconception regarding heat loss through one’s head. You have probably heard one or more of these myths:
- If your feet are cold, cover your head.
- You can lose up to 75% of your body heat through your head alone.
Although 13-16% of the blood volume is in the head at any given time it is a very exposed structure. The problem is that the head is only about 10% of the body surface area. Thus, the head would have to lose about 40 times as much heat per square inch or centimeter compared to the rest of the body to make the above estimate of heat loss true.
Wilderness Medicine[1] took volunteers, wired them to monitor their core temperatures. They discovered humans lose heat through any exposed part of the body and the amount of heat humans lose depends on the amount of exposed surface area. The rate of heat loss is relatively the same for any exposed part of the body not simply the head. You do not lose heat significantly faster through the scalp than any other portion of the body with the same surface area. The idea that we lose heat faster throughout scalp because of the constant blood supply to the brain is simply a myth.
Wilderness Medicine reports the cerebral blood flow is constant; blood flow to the brain does not change as the demand for oxygen is constant. As a result, when you look at total heat loss, the head accounts for about 7% of the heat lost. The cerebral blood flow does, however, vary based on cardiac output – the harder your heart beats, the greater the blood flow to the brain. When you begin to exercise you increase the blood flow to the brain and increase the percentage of heat loss through the head to about 50% of total body heat loss. But as a person continues to exercise, the muscles demand more oxygen which increases blood flow. To ensure thermoregulation and maintain normal core temperature (exercises increases body heat), the skin vasodilates which increases blood flow to the skin to cool the blood. The net result is a decrease in the total blood flow to the brain and a decrease in percentage of total body heat lost through the head to about 10%. Once sweating begins, the percent lost through the scalp returns to 7%.
Research at the Army Research in Environmental Medicine labs showed that there was a temporary increase in heat loss through the scalp that returned to the baseline of 7% as the subjects continued to exercise.
CNN published a set of 10 health myths[2] including heat loss through one’s head: “You Lose 75 Percent of Your Body Heat Through Your Head”. CNN reports the truth is: “This adage was probably based on an infant’s head size, which is a much greater percentage of the total body than an adult head”. That’s why it’s important to make sure an infant’s head remains covered in cold weather. (This also explains those ubiquitous newborn caps at the hospital.) But for an adult, the figure is more like 10 percent. And keep in mind that heat escapes from any exposed area (feet, arms, hands), so putting on a hat is no more important than slipping on gloves.
It is still a good idea to put on a hat if your feet are cold. But what is BUSTED is that there is nothing peculiar or unique about the head. The idea that we lose heat faster throughout scalp, because of the constant blood supply to the brain, is simply a myth.
Layering for your head
The practice of layering is commonly used to keep our torso warm and extended to our feet and hands with over-boots and choppers over mittens. But the head is one extremity that often gets ignored. In severe cold it is useful to combine hats, neck gaiters, scarves and hoods to keep your head and neck warm.
There are several styles of head coverings. Options include a togue-beanie-watch cap, neck gaiter or buff, down hats, balaclavas, face masks, an insulated cap with ear flaps and scarves.
On all these hats, I personally avoid any kind of windblock or waterproof-breathable membranes which limit their breathability and versatility. I prefer to layer extra head coverings as needed, but maintain breathability.
You can stuff damp glove liners into the top of a more spacious hat, and your body heat will dry them out.
Togue, beanie or watch cap
A togue-beanie-watch cap made from fleece or wool hats is good choices. Watch caps or similar close-fitting designs make putting your hood up an easy task. A variation of the togue is a Sherpa or snowboarder’s hat which has flaps that extend down to the cheeks.
Neck gaiter
The fleece neck gaiter or buff option uses soft, double-layered brushed acrylic fleece to trap air to keep neck warm. It can be made into a hat shape that can open further for venting if needed. Fleece dries quickly; insulates even when wet and can provide valuable warmth.
Down or synthetic puffy hat
I never used a puffy hat but for hanging around the campsite or sleeping, some people swear by them. A popular option is the Black Rock down hat. The Black Rock Hat is made with ultralight ripstop fabric, 900 fill goose down, and lined with soft wicking dryline so it molds to your head and stays comfortably in place. The hat is very light – .9 ounces. This is an 1-½ ounces less than the lightest weight fleece hat. It balls up to just a bit larger that a golf ball, so it takes up almost no space. The hat could be just a little longer, as it did tends to ride up a little with movement. Be advised, when you are active you put out a lot of heat and a puffy hat will suffer the same problem as a puffy jackets: moisture build up, with the long term effect that sweat and salts all compromise the loft. Still these hats are light and warm.
Balaclava
A balaclava looks like an executioner’s hood and provides full coverage for your head. These leave either your face exposed (which is good for ventilation) or have just an eye slit (which is warmer, but can collect moisture from your breath). Either way, make sure you buy one that’s long enough so the bottom edge will meet your jacket collar to ward off drafts. You can layer a balaclava with a fleece or wool hat or a hood for extra warmth.
Face Mask
Usually made of neoprene or fleece, this provides crucial protection for your face, which – as it spends all day breaking trail through the wind – is vulnerable to frostbite.
A cap with ear flaps
These hats are usually fleece lined with a baseball cap style brim and long ear flaps. Since I routinely wear glasses the brim is useful not only for shade but also to help keep snow and moisture off my glasses. It has to be a serious wind blast to make me employ the hook and loop closure.
I have a Columbia Kazoo Hat. I usually wear the ear flaps loose as the hat fits securely. The long ear flaps keep my ears and neck warm even in a strong wind. The feature I like the most is the ability to temperature control. Unlike a beanie or watch cap the hat can be adjusted to provide more ventilation. As things warm up the ear flaps can be fastened across the back of the hat and gradually raised towards the top of the hat exposing my neck and head as it morphs into a baseball cap. The hat easily packs in a coat pocket, and it is surprisingly light weight for being so warm. I got my hat at the local sporting goods store but a web search revealed a variety of sources with cost ranging from $12-15. A variation is a trapper’s or bomber hats as worn by Marge from the movie Fargo, The bomber hat is warm – perhaps too warm to wear during aerobic activity.
Silk Bandana
I read this tip in an article by Cliff Jacobson. He routinely brings a large silk scarf on his northern canoe expeditions. I found a large silk bandana to be a versatile item to take winter camping. A silk bandana is not as absorbent as a cotton bandana, but it is a lot stronger, dries faster, rinses out easier and it does not absorb stains the same way. It scrunches up into a smaller package and silk is 1/3rd the weight. It is superior to cotton for retaining warmth and keeping you dry. It feels smoother against the skin, and is generally more breathable.
I have used it primarily as a neck warmer when I am sleeping. When coaching Boy Scouts I encourage them to never bury their head in a sleeping bag during the night, but the light covering of a silk bandana can be used as a face covering. The bandana can be fashioned into a hat, a hood, an emergency sling, an ear warmer, a first phase water filter or any number of items. On a dog sledding trip in single digit temperatures I used it as a face mask to prevent frost bite on my cheeks.
[1] http://wildernessmedicinenewsletter.wordpress.com/2007/02/14/heat-loss-through-the-head-and-hypothermia/
[2] http://www.cnn.com/2010/HEALTH/08/31/rs.12.health.myths/index.html
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