Summary about the fever

Fever is a physiological response of the body, characterized by a temporary increase in body temperature.
We really talk about fever from a temperature of 37.5 °C: fever is a symptom and not a disease and in itself can be caused by several factors or diseases.
We measure fever with a thermometer, in the case of children we prefer a rectal thermometer, as this is more accurate. Taking an oral temperature is also possible, particularly in older children and adults, in the case of young children it is more complicated. Another relatively accurate way for children over 2 years old is the ear thermometer (in the ear). The temperature at armpit level is less accurate.

Fever is usually accompanied by chills due to the production of heat by the body due to the increase in the “thermostat” in the brain: other symptoms commonly associated with fever are muscle aches, fatigue or headaches.

The fever and its symptoms almost always disappear spontaneously without the need to see a doctor. In some cases, however, a specialist is needed. Be aware that a high fever is more of a problem in children than in adults.

To reduce fever there are several medicines called febrifuges or antipyretics (for example: paracetamol, acetylsalicylic acid or ibuprofen).

We recommend the use of antipyretics only if the fever exceeds 38.5°C, except for medical exceptions, of course.

In case of fever, it is important for the patient to rest in a warm place to limit energy loss. Also, avoid alcohol and drink plenty of fluids to offset dehydration caused by the fever.


Fever is a physiological response of the body and is characterized by an increase in body temperature.

Usual body temperature generally ranges from 36°C to 37.2°C.

In case of infection, inflammation or certain diseases, the body temperature can increase above the value considered normal, this is a defense reaction of the organism against the aggressors.

We speak of fever from a temperature of 37.5°C, considering more or less (±) 0.4°C of individual variability in body temperature and also possible changes throughout the day (lowest in the morning, higher at night). It is estimated that the temperature is lower in the morning, around 6:00 am and the highest occurs at night, approximately at 6:00 pm.

This variation occurs due to the production of cortisol, a hormone secreted especially in the early hours of the morning, which has potent anti-inflammatory activity and thus reduces body temperature, for example, after an infection. It is estimated that the temperature is lowest around 06:00 in the morning and highest at night, especially between 18:00 and 20:00. It is necessary to know that the body temperature varies from one organ or region of the body to another.
Body temperature also depends on other factors such as age, physical activity, the season (eg winter compared to summer), digestion or the menstrual cycle in women.

Fever is really a symptom and not a disease. In general, however, fever is associated with other symptoms (headache, aches and pains). In many cases fever is a defense mechanism of the body, raising the body temperature to prevent the proliferation of microorganisms that can then cause an infection. This is why it is important to use antipyretics when the fever is high (above 38.5°C) because fever has its own rationale at the physiological level.

History of fever in medicine
The German physician Karl Wunderlich was the first to present fever as a symptom and not as a disease. In 1868, after extensive research, he defined the normal temperature of the human body, placing it between 37 and 37.5°C.

Questioning Karl Wunderlich’s Theories
Mr. Wunderlich was questioned by modern medicine approximately 150 years after its publication. Some scientists estimate that there is too much temperature difference between individuals to define a precise fever threshold starting at 37.0°C or 37.5°C.
Furthermore, a study carried out by researchers at Stanford University (California, USA) concluded that in 2020 the average body temperature was not about 37°C, but about 36.4°C (or about 97, 5° F), i.e. significantly lower than previously thought. Humans are taller, fatter and live longer than they did in the 1860s, which researchers say may explain this drop. To reach these conclusions, scientists analyzed body temperature data over a period of 157 years, taking into account 189,338 people and 677,423 temperature measurements.1 . This study published January 7, 2020 in the scientific journal eLife2 observed that over the years the average body temperature tended to decrease.

You should know that the hypothalamus, in the brain, regulates the body’s temperature.
Core temperature is defined as the measurement in the pulmonary artery. It is estimated that measuring the temperature in the rectum (anus) reflects the core temperature very well3.

fever and flu

A Canadian study published in 2014 showed that in cases of influenza the administration of an antipyretic (to reduce fever) increased the number of deaths by 1 to 5%. A fever, without being too high, helps the body fight the flu virus. If the temperature is lowered, the virus can easily multiply. The risk of using antipyretics is relevant due to the fact that the patient feels cured and is still contagious, which favors the emergence of flu epidemics.


Fever can be caused by a number of factors (such as exogenous pyrogens, that is, elements outside the body capable of causing fever) or disease.

– Infectious agents such as viruses, bacteria, protozoa or fungi (which cause diseases such as: cold , flu , meningitis , avian flu, sore throat , gastroenteritis , measles , malaria , rubella ), coronavirus Covid-19 .

Infections are the main cause of fever.

– Foreign bodies (allergens, transplant)

– Cancer cells

– Change in an organ or tissue (infarction)

– Medicines or drugs such as: antibiotics, allopurinol , phenytoin, antiarrhythmics, amphetamines, cocaine, atropine or chemotherapy.
When drugs are the cause of fever, we call it drug fever (FM).

– Certain diseases such as  lupus

– Heat exhaustion or advanced sunburn

– Intense physical exercise

– The menstrual cycle in the case of women

– Inflammatory diseases such as rheumatoid arthritis

– Immunizations such as vaccination

Biochemical mechanism
The body cells responsible for the immune defense come into contact with these pyrogens and then release substances called cytokines, responsible for the onset of fever.


It must first be pointed out that fever is often a symptom (and not a disease) of a characteristic problem of the body which may be associated with symptoms other than fever such as, for example, muscle or bone pain, headache, fatigue or pain.

The fever is, usually in its onset, accompanied by chills because of the production of heat by the body.

The fever mechanism can be compared to a thermostat installed in a house to signal and regulate the temperature.

In fact, when the fever increases (for example, at the beginning of cooling) the organism emits substances that increase the temperature of the “thermostat” of the brain.

Thus, the body understands that the normal temperature is higher than 37°C, for example, 39°C. This is why we can feel chills at the early onset of fever because the body is cold (as it is below the value of the brain’s “thermostat”) and therefore reacts by gradually increasing the body temperature to the value of 39°C (to this example).

Conversely, when the fever drops (for example, after taking medication) we sweat and feel hot, because the thermostat goes back to 37°C, but the body temperature is 39°C, we have to remove the sweat and this heat. In this case, to accelerate the reduction of the fever, a cold bath is justifiable and advisable. Attention, even so, the cold bath is increasingly not recommended for children due to the risk of seizures (see good advice).

The fever usually disappears after a few days.


Diagnostics (temperature measurement)

Rectum (anus) measurement

We measure fever with a thermometer, preferably with a rectal thermometer (through the rectum or anus), at least in children, because it is the most accurate.

Measurement under the tongue (in the mouth)
Taking the temperature by mouth (also known as sublingual measurement) is also possible, especially in older children and adults, it is more complicated in young children.

Ear measurement
Another relatively accurate way for children over 2 years old, some sources speak of 18 months, is the auricular (ear) thermometer. Before 18 or 24 months, the ear canal is too narrow for such a measurement.
However, there are critical studies regarding measuring the temperature in the ear.
Despite this, especially in Switzerland, more and more pediatricians and general practitioners are measuring the temperature with an ear thermometer in both children and adults. This method is less invasive and intimidating than measuring rectally and is more accurate than measuring under the tongue or in the armpit.
Your pharmacist can help you select and correctly use an ear thermometer.

Taking a temperature in the armpit
Taking a temperature in the armpit (also known as axillary measurement) is less accurate, some specialists recommend that in this case the temperature taking should last 4 minutes.

Taking core temperature
This measurement, the true temperature measurement, can take place in a hospital or clinic. The measurement can be performed mainly at the level of the distal esophagus, bladder or nasopharynx.

Also read below under Tips for how to properly measure fever.


In most cases, the fever and its associated symptoms resolve spontaneously, without causing any complications and therefore without the need for treatment by a healthcare professional. However, consult a doctor in cases of:

– Fever greater than 40°C

– Fever associated with diarrhea and vomiting

– Fever lasts for several days without abating

– Fever above 39°C in people at risk (for example: children or elderly people with health problems, people with heart or breathing problems)

Attention, non-exhaustive list, for any suspicious symptoms, consult a doctor.

In young children, febrile seizures may occur. An infectious disease is often the source of the problem that occurs in the brain, as a response to the rapid rise in body temperature. According to the Mayo Clinic , the vast majority of febrile seizures do not cause any long-term effects. The reference American institution ( Mayo Clinic ) recommends, in case of febrile convulsions in children, to position the body lying on its side. You will also need to remove any sharp objects from around the child and loosen his clothing.

It is important to know that most febrile seizures end without intervention. After the seizure, it is important to consult a doctor to find out the origin of these attacks. The Mayo Clinic (Mayo Clinic) recommends calling an ambulance if the seizures last more than 10 minutes or if the child has repeated seizures.

According to the Swiss pharmaceutical journal Astrea Pharmacie (December 2019), 2 to 3% of children aged 6 months to 6 years have febrile seizures one day. According to a Swiss pediatrician interviewed by this magazine, these seizures can resemble an epileptic attack. These febrile seizures usually last 1 to 2 minutes, leading to a brief loss of consciousness, eyes rolling. It is not possible to prevent febrile seizures with, for example, the use of medications such as paracetamol. Even if these crises are very impressive, they do not leave a sequel.


Remember again that it is only when the body temperature is above 38.5°C (unless medically recommended) that medication should be taken.

Antipyretic drugs (which reduce fever) act on the symptom and not the cause of the fever: they are only useful for the fever, but not for accelerating or facilitating the treatment of the infection. Sometimes, therefore, the inappropriate use of antipyretics can affect the ability to treat the underlying bacterial infection.

against fever

To reduce fever, the following febrifuge (antipyretic) molecules are mainly used:

– Paracetamol , 500 mg (adult dosage): is the first choice, especially for children! (For dosage and posology for children, ask your doctor or pharmacist).

In children, it is necessary to focus on oral forms, the rectal form (suppositories) is not recommended, as there may be differences in absorption from one child to another. Ask your pediatrician. In cases of children, take paracetamol based on the dose by weight every 6 hours, 4 times a day, consult your pharmacist or doctor (pediatrician).

Paracetamol in case of fever caused by Covid-19 (Novel Coronavirus)
Anti-inflammatories such as ibuprofen are generally not recommended against infection by the new coronavirus Covid-19 , as they can be an aggravating factor in the infection by Covid-19, such as noted French Health Minister Olivier Véran on his Twitter account on March 14, 2020. The Minister noted that in case of fever, paracetamol should be taken. If a person is already taking anti-inflammatory drugs or if in doubt, they should consult their doctor.

– Acetylsalicylic acid (ASS), 500 mg (adult dosage): avoid administering this medication to children, low risk but possible of developing Reye’s symptoms. This syndrome is rare but often serious, even fatal, because it causes damage to the brain and liver.

It is estimated, therefore, that the use of aspirin in children decreased significantly during the first years.

– Ibuprofen , 200 to 400 mg (adult dosage)


If your fever is caused by an infectious disease like the flu or a cold, here are some tips:

– Keep warm and at rest to save energy (your body needs a lot of energy).

– Eat light foods.

– Drink sugary drinks and mineral-rich foods (broths) to replace lost water and nutrients.

– Drink plenty of fluids (about 2 liters a day) to compensate for dehydration caused by fever. Drink water or herbal teas, for example linden based.

– Avoid taking medication to reduce fever if the temperature is below 38.5°C as the fever can help fight infections (increase the body’s defenses, including increasing the number of lymphocytes to fight infectious agents).

– Taking a bath several degrees below body temperature for about 15 minutes helps reduce fever. In cases of children, many pediatricians advise against bathing, as this can lead to seizures due to the temperature dropping too quickly, talk to your pediatrician.

– Avoid overheating apartments in winter

– Take medicines that contain vitamin C , zinc and/or echinacea , these substances have positive effects on infectious diseases (which can cause fever) and act as immunostimulants. They are useful if the fever is caused by an infectious disease as it can help treat the cause.

– Refrain from smoking and drinking alcohol

– If the cause of the fever is unknown and/or the fever persists for a prolonged period, consult a doctor.

– In case of fever before the age of 3 months, it is absolutely advisable to consult a doctor quickly, for example by going to the emergency room. The aim is to quickly identify a possible infection and start treatment, for example with antibiotics.

Fever measurement tips:
– Measure fever, if possible, with the same device (eg thermometer) and at the same body site. This will allow you to properly compare results, as there may be differences between devices and between body sites. For example, a measurement in the rectum (more accurate) can be different than in the armpit, in some situations the difference between these two measurements can be -3°C (which means that the rectal temperature can indicate, for example, 40 °C and the temperature in the armpit indicates only 37°C).

Sources & References:
The Wall Street Journal ,  Wikipedia.org in English, page about Mr. Wunderlich , Astrea Pharmacie (December 2019), Le Figaro.fr.

Jeanne Kenney
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I’m a stylist trainer, a content creator, and an entrepreneur passion. Virgo sign and Pisces ascendant, I move easily between my dreams, the crazy world I want, and my feet on the ground to carry out my projects.

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