Body temperature

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Last Medical Review: April 1, 2020
Medically Reviewed by Dr. Elisabeth Vincent Hamelin
Normal Body Temperature (April 1, 2020)

The body temperature is different in different people. Your age, how you feel and what time of day it can affect what body temperature you have. The body can both heat and emit heat. It is needed for you to be able to keep your body temperature at an even level.

The body temperature varies

The internal body temperature of both children and adults is usually between 36 and 37.8 degrees. The temperature varies from person to person. The temperature of the skin can be both higher and lower depending on how cold or warm it is in the environment.

Reasons why your internal body temperature changes

The temperature can also vary depending on different things:

  • The time of day. At night, the temperature often drops. In the afternoon the temperature is always a little higher than in the morning.
  • Age. Older people who have dementia or are in need of help in everyday life may have lower body temperature than others.
  • Physical activity. Physical exertion raises the temperature. For example, in sports or play.
  • You who are ovulating may have about half a degree higher body temperature from ovulation to menstruation. After the menopause, the temperature drops slightly.
  • When you are pregnant, your body temperature is higher.
  • For example, in hyperthyroidism, body temperature increases slowly for several weeks as thyroid hormone thyroxine production increases. Diseases can also cause you to have a fever.
  • Stress and anxiety increase metabolism in the body. It causes the body temperature to rise.

The body temperature is controlled by the brain

The body temperature is controlled by the center of temperature found in the brain. In the skin and further into the body there are nerves that feel heat and cold. They are called sensory bodies. The sensory bodies provide information to the temperature center in the brain about what temperature the body has. The temperature center then controls the body temperature with the help of the nervous system and the hormone system.

The body can change its temperature, partly because the body generates heat and partly because the body gives off heat.

The body generates heat when the body temperature becomes too low

The liver, muscles and brain help to generate heat as your body rests. Sometimes your body temperature can get too low and you get cold and freeze. Then the body must generate more heat.

The movements of the muscles generate heat

One way for the body to generate heat is to increase the activity of the muscles. It happens when you freeze. Then the muscles become tense and small movements occur. It’s called you shudder. This causes the body to generate more heat.

Movement increases body temperature

The body can also generate heat by moving. For example, you can run a distance or move your arms back and forth quickly. The blood is warmed as it flows through the working muscles.

Increased metabolism

Body heat can also increase by increasing metabolism. This means that the processes in the body go faster. This causes heat to be generated. For example, hormones from the thyroid gland may increase metabolism.

Young children especially have fat that forms heat

Young children have a special kind of fat. It’s called brown fat. Brown fat generates large amounts of heat. Brown fat cells contain especially many mitochondria. The task of mitochondria is to generate energy for the body’s processes. Therefore, more heat is generated in brown fat than in normal fat cells.

The body saves heat by reducing blood circulation in the skin

At low body temperature, blood circulation in the skin decreases. Then the body emits less heat and the skin fades as it does not contain as much blood.

The body emits heat when the body temperature becomes too high

The body constantly emits heat. It is to avoid overheating. At rest, the body’s temperature would rise by about one degree per hour if all the heat generated by the body would remain. With movement, the temperature would rise even more.

The most important way for the body to release heat is to change the skin’s temperature.

The body releases heat by increasing the blood circulation in the skin

The blood vessels in the skin dilate as you warm up. The blood is directed to the skin. Then the skin becomes red and warm. The blood is cooled if the temperature surrounding the body is lower. Cooling happens faster if you fan something.

You give off heat when you sweat

There are many sweat glands in the skin. They activate when you get warm. Then the sweat glands secrete a fluid on the skin surface. The liquid consists of water and salt. Then the water evaporates. It cools the blood flowing into the blood vessels of the skin.

When the body gets too hot

Sometimes you can get too hot, for example if you are playing hard in hot weather or sitting in a car without air conditioning when it is hot outside. It can cause you to get heat stroke. Children are more sensitive to heat than adults.

You need more fluid when it’s hot. Be aware if you are kissing less than usual, as this is a sign that you need to get more fluid in you.

When the body gets too cold

The body can be damaged if you become too cold. This can happen if you are exposed to low temperatures or chilly and humid environments for an extended period of time. Sometimes, when someone is drowning or if a person is found unconscious outdoors, the body temperature can be so low that it seems that the person is dead. Then the activity of the heart is very slow. Breathing is also slow. There is a high risk that the heart rhythm becomes irregular due to the low temperature, and at a really low temperature the heart stops completely.

Cooling can be used in some operations

Cooling can sometimes be used in some brain or heart operations. As a result, the tissues use less oxygen. The blood supply to the organ being operated can then be interrupted a little longer than otherwise without any damage.

Fever

Fever means that the body temperature is higher than it usually is. It is the body’s response to infections caused by viruses or bacteria. You shiver and freeze as the temperature rises. You get sweaty when the fever goes down again.

How high your body temperature becomes in case of fever can vary depending on your body temperature when you are healthy. A clear measure of fever is that you feel ill in combination with your body temperature increasing at least a degree from your normal body temperature.

What determines if you are ill is how you feel

The most important thing is not really the temperature. What determines if you are ill is how you feel otherwise. Especially older people and newborns can have serious infections without getting higher body temperature. You can also have a higher body temperature than you usually do without being ill.

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