The chills, goosebumps, the feeling of shivering and the verdict of the falling thermometer: no doubt, you have a fever! Only, why do we have a fever when we are sick? We tell you everything about this body thermo-regulation mechanism.

Summary

Fever, a signal triggered by our brain

How is fever started?

Physiological defense mechanisms

Is fever useful for fighting infections?

Recommendations to follow if you have a fever

When should you consult?

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The thermometer is the flagship instrument of our first aid kits. The one who will answer, in less than a minute, this fateful question: "Are we sick ... or not?". This is often the first question that our general practitioner asks us in consultation: "Do you have a fever?". The fact is that fever is a relentless symptom like knee pain… For doctors and for us! The sign that we are… sick!

Fever, a signal triggered by our brain

So why do we have a fever when we are sick? The case is played on a gland located in our brain: the hypothalamus. " It is a kind of thermostat which will regulate the temperature of our body ", explains Professor Jean-Paul Stahl, head of the infectious diseases department of the Grenoble University Hospital . Normally, this " hypothalamic thermostat" keeps the body temperature at an equilibrium point around 37 ° C. " Between 37 and 37.5 degrees is fluctuating, " says Professor Jean-Paul Stahl. "This temperature can vary throughout the day: it will be lower in the morning and higher in the evening. Body temperature can also fluctuate depending on hormonal status, especially in women, or thyroid hormones . "Physiological variations, up to a point.

How is fever started?

Beyond 38 ° C, we can indeed speak of fever, or "pyrexia". This is the term used in medical jargon to refer to this rise in our body temperature above normal. It is the sign that we are "sick" and thus that our organism is fighting a foreign body…. " Fever is a reaction to an attack, whatever it is ... Most often, it is an attack of an infectious nature: a bacterium or virus ... It is the consequence of an activation of our immune system ", explains Professor Jean-Paul Stahl.

When a pathogen enters our body, the defense cells detect it and will then produce so-called pyrogenic substances, that is to say capable of raising the temperature of our body: these are "cytokines" . These famous cytokines will alert the hypothalamus, this gland located in our brain. The message is clear: it is a question of increasing the level of the " hypothalamic thermostat ". The objective? Produce more body heat to help the immune system fight the attacker.

Physiological defense mechanisms

Then follows a series of physiological adaptations orchestrated by the hypothalamus and aimed at increasing the heat of our body. The gland will send a message to our muscles: " Contract yourself to produce more energy and therefore heat! ". Now you understand better why you also have aches when you have a fever…

The hypothalamus will also orchestrate vasoconstriction. This physiological mechanism corresponds to a decrease in the size of the blood vessels at the extremities of the body. The blood circulation is then reduced to lose less heat through the skin.

Our hairs can also come into play: they straighten up to protect us from the cold. It is the famous "piloerection" better known under the name of "goosebumps" ... " All these phenomena are physiological defense mechanisms ", traces Professor Jean-Paul Stahl. The chills, the impression of shivering (due to the contraction of our muscles) when we are feverish ... Nothing to be alarmed about ... Quite the contrary! This is a sign that our immune system is working at full capacity ...

Is fever useful for fighting infections?

Does the increase in body temperature really harm bacteria or viruses? Nothing is proven… It is above all the sign that the immune system is activated, more than a defense mechanism in its own right.

However, fever has the advantage of being an easy symptom to detect. " It is a warning signal which means" I am not doing well: find out why! "It is also the best marker of the progression of an infection ", underlines Professor Jean-Paul Stahl, chief from the infectious diseases department of the Grenoble University Hospital. " Thus, as long as the fever is well tolerated, other symptoms have not been identified and a medical diagnosis has not been established, it is not recommended to use anti-pyretics (note drugs used in treatment of fever). "This allows not to falsify the diagnosis and to follow the evolution of the disease. Because if the increase in our body temperature above 38 degrees is a sign that we are sick, its return to normal will mean recovery!

Recommendations to follow if you have a fever

DON'T WORRY AS SOON AS YOU NOTICE A HIGH FEVER (IN AN ADULT)

High fever does not have to mean serious illness! " Certain viral diseases give high fevers and are not serious so far ... When other more serious diseases are characterized by a low fever ", details Professor Jean-Paul Stahl.

OTHER SYMPTOMS TO WATCH FOR

" Fever is a reaction to a mild or severe attack. It is the presence of other symptoms that should alert: Is the heart working as it should? And breathing? What is the state of consciousness ... are these other symptoms, which are less obvious to identify and which are the most important and should lead to consulting a doctor ", underlines Professor Jean-Paul.

When should you consult?

When the temperature exceeds 40 ° C .

If you have other more worrying symptoms : heart problems (rhythm disturbances), breathing problems, altered state of consciousness…

Beyond three consecutive days of fever .

These recommendations are valid for adults in good physical health. A very special attention should be given to young children aged 0 to 5 years old and the elderly for whom a consultation for fever, even moderate, is highly recommended.