The temperature of the human body measured under the armpits averages 36.5 degrees Celsius. Studies on a large number of healthy individuals have shown that normal temperature can range from 36 degrees to more than 37 degrees Celsius. Man, along with all other mammals and birds, belongs to the group of warm-blooded living beings. Due to the constant temperature, it does not depend on changes in the temperature of the environment in which it lives. In winter he can withstand very low temperatures, and in summer more than 50 degrees Celsius in the shade, while keeping his body heat unchanged.

The main "conductor" who is responsible for the constancy of body temperature is in the part of the brain called the hypothalamus. The operation of this heat control center can be compared to a thermostat, ie a device that automatically regulates and maintains a constant temperature in appliances, machines, apartments. On a similar principle, only much more complicated, works the "thermostat in the brain" of man. When the temperature in the body rises, the "thermostat" sends commands over a number of nerves to reduce heat generation and increase heat release from the body. If the temperature in the body drops, the orders from the center will be the opposite, ie it will reduce the release of heat and increase the production of heat in the body.

Heat in the body is created by burning food in the cells of organs and tissues. At rest, most heat is created by the work of organs such as the liver (20 percent of total heat), the brain, the heart. The greatest amount of heat will be created by the work of the muscles when they are in action. The heat generated by the blood circulation is evenly distributed throughout the body. Heat is constantly produced, but also constantly lost from the surface of the body in the environment. When the amount of heat generated in the body is equal to the amount of heat the body loses, then there is heat balance in the body. If an increased amount of heat is generated in the body, eg due to increased muscle work, the "thermostat in the brain" immediately takes action: blood vessels in the skin dilate (this makes the face red); the influx of blood coming to the surface of the body increases. In order for as much blood as possible to pass through the skin, the heart works harder and faster. The importance of blood vessels for heat regulation can be easily compared to heating pipes, and the skin of the body with the surface of the radiator through which heat is lost by radiation to an environment where the temperature is lower. If the heat generation in the body is even greater, then the heat loss by radiation is not enough. In that case, the "thermostat" gives the order for increased sweating. Evaporation of sweat significantly increases heat loss from the body.

Measurement of body temperature is most often performed by placing a thermometer under the armpit. Before use, the thermometer should be "shaken" and the mercury level checked. Measuring temperature in the colon is more reliable than measuring under the armpit. This method of measurement is used for inflammatory changes in the abdominal cavity, and so the temperature of young children is measured. The value of the temperature thus measured is half (0.5) degrees Celsius higher than the temperature measured under the armpit. If the temperature thus measured is greater than one degree with respect to the axillary temperature, there is a possibility of inflammation in the abdomen or it is the result of poor measurement technique. In the oral cavity, temperature is measured only in adults. In our country, this method of measurement is very rare. Before measuring, the thermometer must be thoroughly cleaned, disinfected with alcohol, dried and only then used. The thermometer is placed under the tongue. While the thermometer is in the mouth, you only breathe through the nose, because breathing through the mouth cools down, so the result of the measurement would not be accurate. The values ​​of the temperature thus obtained average 37.2 degrees Celsius.

Elevated body temperature is also called fever. Fever is not a disease. Like pain and dizziness, it is just a sign, a symptom of various diseases. A small increase in body temperature can be considered normal; the temperature rises regularly during strenuous physical exertion: hard physical work, participation in strenuous sports; it increases by 1 to 2 degrees Celsius, and can be considerably more, especially if measured in the colon. Mental excitement can be caused by very high temperatures. An increase in body temperature in many diseases works favorably because it leads to faster production of antibodies, the bodies that the body creates to fight the cause of the disease. Elevated body temperature, caused intentionally, is used in the treatment of many diseases. The positive effect of elevated body temperature also depends on the duration. Too high a temperature can in itself become dangerous for the body. Already at a temperature of 41 degrees Celsius, the cells of one's own body begin to be destroyed. A temperature of 42 degrees can be tolerated by a person for only a few hours, and even higher temperatures in just a few minutes.

Newborns and infants in the first months of life are very sensitive to changes in ambient temperature. Cooling and overheating of the body is much more common than in older children and adults. The causes of high temperatures do not have to be infections, which is what parents are most afraid of. Fearing that the child will be cold, worried parents overheat the premises, dress him too warmly, put thermophores in the bed, and as the child cannot regulate his temperature like an adult, heat builds up in the body. Body temperature rises because in the first month of life the sweat glands do not yet secrete sweat. Therefore, the newborn does not sweat despite the high body temperature, and we know that excess heat in high ambient temperatures can be reduced in the body only by evaporating sweat, and if some cooling procedures are not applied urgently, the baby will die.

It is completely wrong to think that fever must be immediately reduced to a normal temperature. Elevated temperature is just one defensive reaction of the body. Complete and sudden normalization of temperature also reduces the body's defenses. Various procedures should be used to calm down too high a temperature only when there is a danger that, regardless of the disease that caused it, it will start destroying one's own body. A man who has a fever should not be on a diet that will starve him; he should eat easily digestible food in smaller quantities and more frequent meals. Food must be rich in vitamins and proteins.

Conditions of very high temperature must be detected quickly and treated as soon as possible. Knowing first aid is extraordinarily important because life-saving measures often save lives. Any increase in body temperature, measured under the armpits, in a value above 41 degrees Celsius, is called a state of very high temperature or hyperpyrexia. Once the body temperature exceeds 41.7 degrees Celsius, the "thermostat" in the body stops functioning, the temperature regulation is totally disturbed, sweating stops, the body temperature is constantly rising. Only rapid cooling can prevent death. When the body temperature drops below the critical limit once, the "thermostat" works again and the body regulates its own heat.

When the creation of heat in the body is less than its loss, the body cools down and the temperature drops. If the skin is exposed to a prolonged effect of low temperature, the blood flow in the skin is reduced to such an extent that any nutrition of the skin is disturbed or almost stopped; there is limited skin damage, frostbite. Frostbite most often occurs on prominent and exposed parts of the body such as the nose, ears, fingers. Some people have a normal temperature below 36 degrees Celsius, but such a low temperature is a sign of many diseases. The temperature is lowered when starving, after prolonged diarrhea and vomiting, after prolonged diving, especially in children. Decreased temperature is also accompanied by long-term, chronic diseases, such as diabetes, anemia, brain tumor, cerebral hemorrhage, decreased thyroid function. Acute drunkenness also lowers the temperature, as well as poisoning by phenol, sleeping pills, phosphorus, atropine.