Losing heat through your head - a myth ?

[Shewie]

I caught the tail end of this on the news today ...

http://www.dailymail.co.uk/health/a...head-Discover-barefaced-truth-hats-myths.html

 

[Treemonk]

I think the message was that it wasn't 50% like your granny used to say - more like 10%. But lets not forget, 10% is still quite a significant fraction.

 

[HillBill]

Actually its more like 30% on average, less if your hair is thick more if thin/shaved/bald so it varies to the extremes of 50%/10% . Remember heat rises, even in your body. Stop it escaping and its trapped within let it out and it'l keep on going.

This is from the article

Writing in the British Medical Journal, they found no evidence that more heat escapes from the head than any other part of the body.

True enough, when your naked. Why then do your hands warm up if you put a hat on?

 

[Mesquite]

Remember heat rises, even in your body. Stop it escaping and its trapped within let it out and it'l keep on going.

I was told it's not to do with the fact that heat rises but the fact you have major blood vessels feeding the head which means the heat is lost through the blood cooling down. Hence scarf and hat are the best combination for keeping warmth in

Also the article does say that the main reason for loosing heat more through your head is simply the head is left exposed the most

 

[HillBill]

I was told it's not to do with the fact that heat rises but the fact you have major blood vessels feeding the head which means the heat is lost through the blood cooling down. Hence scarf and hat are the best combination for keeping warmth in

The blood takes heat from the core as it moves to the head, if that heat is allowed to escape then your body has to compensate for that by trying to produce more heat by shivering. Unless you are physically exerting yourself to generate the heat, the cycle will continue. That is why your extremeties ie hands and feet get cold first because the body will try to replace the heat lost from its core by partly shutting down the flow to those and keep it around the vital organs where its most needed.Wearing a hat and scarf greatly reduces the effort your body has to put out to keep warm. By drawing heat from the extremeties and pumping it first to the core and then to the head means that heat still rises in the body just by a different method. Its pumped up there rather than just rising like heat from a radiator for example.

 

[Hoodoo]

The blood takes heat from the core as it moves to the head, if that heat is allowed to escape then your body has to compensate for that by trying to produce more heat by shivering. Unless you are physically exerting yourself to generate the heat, the cycle will continue. That is why your extremeties ie hands and feet get cold first because the body will try to replace the heat lost from its core by partly shutting down the flow to those and keep it around the vital organs where its most needed.Wearing a hat and scarf greatly reduces the effort your body has to put out to keep warm. By drawing heat from the extremeties and pumping it first to the core and then to the head means that heat still rises in the body just by a different method. Its pumped up there rather than just rising like heat from a radiator for example.

When it's cold, vasoconstriction occurs in the extremeties to minimize heat loss. But because the brain requires oxygen to function, vasoconstiction does not occur in the vessels that supply the head. Since the head is warmer than the environment (assuming cold weather) there is a steep thermal diffusion gradient favoring heat loss from the head to the environment.

 

[HillBill]

Vasoconstriction. I'll rememeber that, i never knew what the process was called. Thanks.

 

[wicca]

When I remarked to my Doctor that my head always seemed to feel cold he said, "Well you can't heat a vacuum" :bluThinki Wonder what he meant?

 

[jojo]

Wonder what he meant?

I think the cheeky so and so meant he thought you were empty headed It may be true, of course but it's still some cheek :yelrotflm :yelrotflm

Anyway, I like wearing my hat, and that's come out of a newspaper so I am not going to take any notice and continue wearing it and a scarf

Besides, I need an excuse to buy myself another nice new felt hat!

 

[wicca]

He's certainly on the right track To return to the serious side of what HillBill and Voodoo were saying, I found the last time I slept out a wooly hat worn in the sleeping bag seemed to make a huge difference in comfort.

 

[jojo]

I found this article. It seems that heat loss thorough the head can vary from about 7% to up to 50% depending on the level of activity and the weather conditions. I certainly won't stop using something on my head just because of that article. It does not seem to make sense to me to cover your whole body and then leave your head uncovered. If your head/hair gets wet, that would speed up your head loss too.


March, 2008

Barry S. Brown, University Professor of kinesiology in the College of Education and Health Professions, replies:

In general, heat loss is essential to provide thermoregulation and prevent excessive heat build-up in the body to avoid the consequences of heat stroke. However, heat loss in the head is the same as for any exposed body part. The exposed surface area of the body, along with relative humidity and temperature, determines heat loss primarily through evaporation and our head makes up only 10 percent of body surface area. So, at rest, heat loss through the head accounts for only 7-10 percent of total heat dissipation.

The brain is supplied by blood flow through the cerebral and vertebral arteries, which also supply oxygen and heat to the brain. This flow does not change since the oxygen demand to the brain is constant. However, as cardiac output is increased, the blood transported via the cerebral arteries to the brain also is increased. This increase in blood flow to the brain also results in an increase in the percentage of heat loss. As you begin exercise, cerebral blood flow increases due to increased cardiac output and the percentage of heat lost through the head accounts for about 50 percent of total body heat loss. As exercise continues, more oxygen is directed toward muscle and blood flow to this tissue increases. Core temperature has to be maintained and as body heat increases, the skin arterioles expand, or vasodilate, redirecting blood flow to the skin which cools the blood. Hence, total blood flow to the brain is decreased and the percentage of total body heat lost through the head is reduced to about 10 percent. The percent lost through the scalp returns to 7 percent after sweating begins.

One important caveat occurs during hypothermia, or cold exposure. If shivering occurs during hypothermia, 55 percent of the heat loss can occur in the scalp. Therefore, head covering during cold weather is strongly advised.

 

[Scots_Charles_River]

If you measure the surface are of the head/scalp and the importance of the brain compared to say legs, it is worth it. Winter climbing - fire a hat on at the summit makes a big difference. Ears lose a lot of heat due to being thin and a large area.

Nick

 

[HillBill]

So the basic jist is, The daily Mail chats shiite

 

[crazyclimber]

10% or 70%,

fire a hat on at the summit makes a big difference

what he said is right!

Article on the same thing http://news.bbc.co.uk/2/hi/health/7789302.stm

If the experiment had been done with the participants wearing only swimsuits they would not have lost more than 10% of their body heat through their heads, the researchers said.

Makes sense I guess. Wearing a couple layers on a mountain I could quite believe not wearing a hat = 50% heat loss from the head

 

[Rebel]

These articles are syndicated and printed in several newspapers. Often they are a load of codswallop and a contradictory article will come out a few weeks later confirming that Grandma was right all along.

Anyway, whatever the science, I know I feel a lot warmer with a hat on. It makes a big difference to my overall body heat. In cold weather it makes sense to wear one, why have a cold head and ears when you don't need to?

 

[jojo]

The problem with these scientific research is that they sometimes look at a very narrow interpretation of the subject they are investigating, and I don't think they always come up with meaningful answers in the real world.

And the way it's presented by journalists that may or may not have any scientific training can sometimes be misleading to say the least.

Don't cover a large bit of yourself, like your head, get that bit wet and then stand in the wind and see what happen to you.... Hypothermia comes from somewhere.

 

[Shewie]

I must admit I feel a lot warmer with a hat on and it`s nice to be able to pull something down over the old lugs to keep the cold wind out.

 

[The Cumbrian]

I suspect that these tests were made with a thermal imaging camera of a naked subject in lab conditions.

As a less scientific test, how many hatless farmers have you ever met?

 

[BOD]

Exactly.

The relative heat dissipation from parts of the body is irrelevant to an outdoors person.

What is important is heat retention through clothing.

Leave the head bare + the brains need for blood flow = losing body heat.

Someone will not read the article carefully or listen to his mates inaccurate account and decide that they do not need a hat with potentially serious consequences.

Well so what its only Daily Mail readers and their friends

 

[Hoodoo]

The problem with these scientific research is that they sometimes look at a very narrow interpretation of the subject they are investigating, and I don't think they always come up with meaningful answers in the real world.

And the way it's presented by journalists that may or may not have any scientific training can sometimes be misleading to say the least.

Don't cover a large bit of yourself, like your head, get that bit wet and then stand in the wind and see what happen to you.... Hypothermia comes from somewhere.

The vast majority of journalists are scientifically illiterate. I rarerly trust a journalist's interpretation of a research paper. Science News does a good job of reporting on science.