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Why You Feel So Hot When You Have a Cold
(Pyrexia - Fever)

By Dr. Peter W. Kujtan, B.Sc., M.D., Ph.D.

Article printed on page 42 in the November 21, 2012 issue of
The Mississauga News under the feature: Health & Beauty, Medicine Matters.
Portrait of Dr. Peter W. Kujtan, supplied 2005
Dr. Peter W. Kujtan

Pyrexia is the medical term for fever. If your body temperature increases to beyond 37.2° C, and you begin to sweat, breathe deeper and feel warmer, that’s when I tell you that you are running a fever.

The commonest cause of fever is the simple cold. This condition is well known to all of us, with the scratchy throat and runny nose. The body thermostat is found in the hypothalamus within the brain. Pyrogens are a group of substances released from inflammatory cells, which have the capability of resetting the hypothalamic thermostat to increase body temperature. Inflammatory cells spring into action when the body is invaded by foreign viruses or bacteria. If I increase your central thermostat by a few degrees, your body will think that it is too cold, and you get that “chilled” feeling.

This explains one of the great myths of colds. Many mothers tell their children that the reason they got a cold is because they went outside poorly dressed and got chilled. In reality, the cold virus is highly contagious and there is a time delay between the virus invading through your nose and developing symptoms. Being out in the cold has nothing to do with contagiousness, it simply exaggerates the chilled feeling.

Pyrogens can be produced by viruses and bacteria or by many cells in our immune system. In this way, fever is a beneficial state in which our immune system seems to function better. Increased body temperature increases our body enzymatic processes and facilitates the quick mobilization of our immune system.

Technically, fever is not due to infection, it tells you that your body is fighting back.

We also see fever with other entities such as cancer. A group of glycoproteins produced by immune cells is called the Tumor Necrosis Factor (TNF), which turns up the thermostat in the hopes of having immune cells mobilize towards cancer cells. It is high fever of over 40° C that we express concern because it may signal an overwhelming of our system. This could result in malfunctioning of cellular machinery leading to febrile seizures in children. This is why we advocate the use of anti-pyrogens such as acetaminophen to control the amount of fever and discomfort.

The common cold is actually caused by hundreds of different and related viruses. Your body will respond to over a hundred different cold causing viruses during an average lifespan. A great many of these cold illnesses will occur in the first part of life. Immunity is thought to be permanent after each bout.

Colds are not caused by a “weakened” immune system. This is a myth. If I take 100 people, put them in a room and spray in a new cold virus, about 90 people will become infected. But 25 of those infected will have their immune system quietly deal with it and show no symptoms at all.

Cold viruses are spread not only in the air, but settle on objects when you cough. They can survive there from minutes to hours. Washing our hands and covering our mouths are still the best defence. Colds rarely keep healthy people from school, work or lending a hand when your team needs to put a few buffalo chips in the net on the frozen pond! So, try and stay healthy this season. And get those skates sharpened!

Related resources:

Fever from Wikipedia.

Fever from MedlinePlus.

What Is Fever (Pyrexia)? What Causes Fever? From Medical News Today (MNT). "Fever, pyrexia or controlled hyperthermia is when a human's body temperature goes above the normal range of 36-37C (98-100F) - it is a common medical sign. As the individual's body temperature goes up, there may be a sensation of cold until the temperature plateaus (stops rising).

An elevated body temperature (fever) is one of the ways our immune system attempts to combat an infection. Usually the rise in body temperature helps the individual resolve an infection. However, sometimes it may rise too high, in which case the fever can be serious and lead to complications."

Fever in Children from NHS.uk. "A fever is a high temperature. As a general rule, in children, a temperature of over 37.5°C is a fever. Most fevers are caused by infections or other illnesses. A fever helps the body to fight infections by stimulating the immune system (the body’s natural defence against infection and illness).

By increasing the body’s temperature, a fever makes it more difficult for the bacteria and viruses that cause infections to survive. Common conditions that can cause fevers include: flu, ear infections, roseola, tonsillitis, kidney or urinary infections, common childhood illnesses, such as measles, mumps, chickenpox and whooping cough."

Fever in Adults: Causes, Treatment, Prevention from eMedicine Health. Medical Author: Charles Patrick Davis, MD, PhD. Chief Medical Editor: Melissa Conrad Stöppler, MD. "Illnesses caused by viruses are among the most frequent causes of fever in adults. Symptoms can include a runny nose, sore throat, cough, hoarseness, and muscle aches. Viruses also may cause diarrhea, vomiting, or an upset stomach.

For the most part, these viral illnesses will improve simply with time. Antibiotics will not treat a virus. Symptoms can be treated using decongestants and anti-fever medications bought over the counter."

What Causes a Fever from Scientific American, by Peter Nalin, Indiana University. "Fever is an elevated temperature of the human body that is substantially beyond the normal range. Normal body temperature fluctuates daily from about one degree below 98.6 degrees Fahrenheit to one degree above that number. Lower body temperatures usually occur before dawn; higher temperatures in the afternoon ...

The presence of a fever is usually related to stimulation of the body's immune response ... Infectious agents are not the only causes of fever ... Amphetamine abuse and alcohol withdrawal can both elicit high temperatures ... And environmental fevers--such as those associated with heat stroke and related illnesses--can also occur.

The hypothalamus, which sits at the base of the brain, acts as the body's thermostat. It is triggered by floating biochemical substances called pyrogens, which flow from sites where the immune system has identified potential trouble to the hypothalamus via the bloodstream ... Children typically get higher and quicker fevers, reflecting the effects of the pyrogens upon an inexperienced immune system.

Should one eat little or nothing while feverish, as the saying "Feed a cold, starve a fever" suggests? Yes. The reasons for this are threefold ... Finally, excessive fever can, on rare occasions, cause seizures, collapse and delirium--all of which may be further complicated by recent eating ..."

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