Many explain the need to wear a hat in the cold season by the fact that most of the heat goes through the head. We decided to check whether this fear is supported by scientific data.
Counts, What majority heat from human body leaves precisely through head, so it's like that important in the cold weather wear hat. About this write V blogs, social networks And Media. Official institutions also post such information, for example “Center for Public Health and Medical Prevention» Sverdlovsk region and South Ural State Agrarian University. Explain This is usually because heat always rises.
Heat transfer is the physical process of transferring thermal energy from a hotter body to a cooler one. If we talk about living organisms, their ability to maintain their body temperature even at different ambient temperatures called thermoregulation. Thermoregulation center located in the hypothalamus. This part of the brain controls the most important organs for thermoregulation - the adrenal glands and the thyroid gland. They, in turn, produce hormones that accelerate metabolism, and thus increase heat generation.
In general, human heat exchange depends from a number of factors - physical (body shape and size) and physiological (blood flow, sweating, hair growth). Let's deal with each of them.
Heat faster lose large in surface area. Heat leaves a flat but large surface much faster than a volumetric surface, such as a spherical one. Since the head is spherical (the shape with the smallest surface area to volume ratio), heat transfer will not be as intense as with flatter parts of the human body, such as the hands or feet.
The blood supply to the head is indeed extremely active, so even a minor injury in this area entails significant bleeding. However, the vessels of the head and face are not very pronounced react to increase and decrease in temperature. In 1993, Canadian scientists used Doppler sonography to study how blood flow in these vessels changes during hypo- and hyperthermia. During cooling, which was achieved by placing the subjects in water at a temperature of +21.5 °C, the blood flow to the face and head of the volunteers remained almost unchanged, but in water at a temperature of +35 °C, the blood flow speed increased significantly - three to nine times. From the point of view of changes in blood flow speed depending on temperature, the feet and hands turned out to be the most quickly reacting, respectively, quickly heating up and quickly cooling down.
The next parameter is sweating. The body cools down by evaporating sweat from the skin. More The total number of sweat gland ducts is located on the inside of the hands, but as the temperature rises, the most sweat is produced on the forehead. However, due to the small area of the forehead (there are significantly fewer sweat glands on the rest of the head), the evaporation of sweat from the head amounts to only 10% of the total.
Finally, hair retains heat quite effectively, as it insulates the surface of the head from heat transfer. Of course, not all heads are covered with hair and not every hairstyle effectively protects from the cold - for example, thick and curly hair, which creates more volume, will retain the heat of the head much more effectively than short-cut and straight hair. There is no exact data on the number of people without hair on their heads in the world, since medical and statistical resources are only interested in counting those who have lost their hair due to genetic, age-related and other factors and do not take into account those who simply prefer this hairstyle. However known, that almost 43% of the male population of the Czech Republic and Spain, 41% of Germany and 39% of the USA experience baldness.
Thus, based on the sum of physical and physiological parameters, the head should be one of those places in the human body that is least susceptible to heat loss. Rachel Vreeman and Aaron Carroll of Indiana University Health Services in Indianapolis figured it out, where the myth about the greatest loss of heat through the head came from. In the 1950s, the US military conducted experiments on survival in Arctic conditions. The volunteer soldiers wore special arctic suits, but for some reason they were not given hats. The head cooled the most, as a result of which the experimenters came to this conclusion. Moreover, the results of their research hit and in the 1970 US Army Survival Manual under “Cold Weather Survival”: “Always keep your head covered. Between 40% and 45% of heat is lost through an unprotected head, and even more through an unprotected neck, wrists and ankles.” Vreeman and Carroll comment this myth: “In fact, covering one part of the body has the same effect as covering any other. If the experiment were carried out on people wearing only swimming trunks, they would lose no more than 10% of their body heat through their heads.”
The number 10% is confirmed by scientific experiments. Thea Pretorius from the University of Manitoba in Canada immersed volunteers in cold water (+17 °C). They either wore a full waterproof suit and submerged their heads, or wore a similar suit but with their heads exposed, and were then submerged with their heads on the surface. It should be noted that all of them were distinguished not only by endurance, but also by good hair. There were no bald people in the experiment. It turned out that those who plunged underwater in a waterproof suit lost half as much heat as those who, wearing the same headless suits, stayed on the surface. At the same time, there was a small heat loss on the head - only 7–10% of the total. These data are in good agreement with the fact that the head area amounts to approximately 9% of the total body area.
Thus, the myth that the greatest heat loss occurs through an uncovered head was born due to not entirely correct experiments by the American military. Basically, each part of the body loses heat in proportion to its area. The feet and hands are slightly more susceptible to severe heat loss due to their structure and blood circulation. The head accounts for approximately 10% of the body’s total heat loss. At the same time, this is by no means a reason to walk in severe frosts without a hat, but in warm shoes and woolen mittens, calculating that heat loss of 10% can be neglected.
Cover image: Image by Ri Butov from Pixabay
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