Many explain the need to wear a hat in the cold season by the fact that most heat leaves through the head. We decided to check if such a fear is confirmed by scientific data.
Counts, What majority heat from human bodies Leaving It is through headso so important In cold Weather wear hat. About this write V Blogs, social networks And Media. Place such information and official institutions, for example, "Center for Public Health and Medical Prevention»Of the Sverdlovsk region and South Ural State Agrarian University. Explain This is usually because heat always rises up.
Heat transfer is a physical process of transmitting thermal energy from a more hot body to less hot. If we talk about living organisms, their ability to maintain their body temperature even at a different external temperature called Thermoregulation. Thermoregulation center located In the hypothalamus. This section of the brain controls the most important organs for thermoregulation - the adrenal glands and the thyroid gland. Those, in turn, produce hormones that accelerate the metabolism, and thus intensifies heat formation.
In general, human heat transfer depends From a number of factors - physical (form and size of the body) and physiological (blood flow, sweating, exposure). Let's figure out each of them.
Heat is faster Lost Large in surface area. With a flat, but large surface, heat leaves much faster than with voluminous, for example, spherical. Since the head has a spherical shape (figures with the smallest ratio of surface area to volume), heat transfer will not be as intense as in the case of more flat parts of the human body, such as brushes or feet.
The blood supply to the head is indeed extremely active, so even a small 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 with the help of dopplerography studied how the blood flow in these vessels changes during hypo- and hyperthermia. When cooling, which was reached, placing the subjects in water with a temperature of +21.5 ° C, the blood flow of the face and head of volunteers almost did not change, but in water the temperature of +35 ° C increased significantly-three to nine times. From the point of view of changes in the velocity of blood flow, depending on the temperature of the feet and the brush, the most Quickly reacting, respectively, rapidly heat and quickly cool.
The next parameter is sweating. With the help of evaporation of sweat from the skin, the body cools. More In total, the ducts of the sweat glands are located on the inside of the hands, but with an increase in temperature, the most of the sweat is produced on the forehead. However, due to the small area of the forehead (on the rest of the head of the sweat glands there are much smaller), the evaporation of sweat from the head It is Only 10% of the total.
Finally, the hair is quite effectively held by heat, as it isolate the surface of the head from heat transfer. Of course, not all heads are covered with hair and not any hairstyle effectively protects against the cold - so, thick and curly hair that create a larger volume will retain the warmth of the head more efficiently than short -cut and straight. There is no exact data on the number of people without hair on the head in the world, since medical and statistical resources are only interested in the calculation of those who have lost their hair due to genetic, age and other factors and do not take into account those who simply prefer such a hairstyle. However It is knownWhat is precisely with baldness, almost 43% of the male population of the Czech Republic and Spain, 41% of Germany and 39% of the United States are faced.
Thus, according to the sum of physical and physiological parameters, the head should be one of those places of the human body that is the least susceptible to heat loss. Rachel Vrimiman and Aaron Carroll from the University of Indiana University in Indianapolis I figured it out, where did the myth of the greatest loss of heat through the head come from. In the 1950s, the American military conducted experiments on survival in the Arctic conditions. Volunteer soldiers wore special Arctic costumes, but for some reason they did not give their hats. The head cooled the most, as a result of which the experimenters made such a conclusion. Moreover, the results of their research hit And in the 1970 Army in the US Army in the section “Survival in cold weather”: “Always keep your head covered. From 40% to 45% of heat is lost through an unprotected head, even more through an unprotected neck, wrists and ankles. ” Vrimiman and Caroll Commented This myth: “In fact, the coating of one part of the body has the same effect as the coating of any other. If the experiment were conducted with people dressed only in swimming trunks, they would have lost no more than 10% of the body's body through their heads. ”
The number 10% is confirmed by scientific experiments. Thea Praetorius From the University of Manitobe in Canada I immersed Volunteers in cold water (+17 ° C). They were either completely dressed in a waterproof costume and plunged with their heads, or wore a similar suit, but with their head open, and then they were loaded so that the head remained on the surface. It should be noted that all of them differed not only with endurance, but also with good hair. There was no bald in the experiment. It turned out that those who plunged under water in a waterproof suit lost two times less heat than those who, in the same suits without a head, kept on the surface. At the same time, a small heat loss came on the head - only 7-10% of the total. These data are well consistent with the fact that the area of the head It is About 9% of the area of the whole body.
Thus, the myth that the greatest heat loss is through an uncovered head was born due to the not entirely correct experiments of the American military. Basically, each part of the body loses heat in proportion to its area. Feet and brushes are a little larger-due to the features of the structure and blood circulation. The head accounts for about 10% of the total heat loss of the body. 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, hoping that heat losses of 10% can be neglected.
Image on the cover: Image by Ri butov from Pixabay
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