Fever: causes and treatment

Fever: causes and treatment

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What to do if you have a fever?

It can be assumed that everyone has had a fever in the course of their life, although the causes and the severity can vary greatly. First of all, fever is a defense reaction from the body. The increased temperature supports the immune system in fighting pathogens. In adults, a body temperature of up to 39 degrees Celsius is more likely to promote healing. However, since fever is a symptom of a large number of illnesses and can also indicate serious illnesses in some cases, a doctor should be consulted if the temperature remains high or if there are additional symptoms.

Fever - the most important in a nutshell

Fever is not an independent disease. It is a defense mechanism that our bodies use to react to viruses and bacteria that can no longer reproduce so well at higher body temperatures. Fever is therefore an important part of natural defense. Often no antipyretic measures are necessary. Nevertheless, an elevated body temperature should always be kept in mind and should be checked with a doctor if it rises too high or does not go away on its own within a few days. Here is a brief overview of the symptoms:

  • definition: From a body temperature of 38.2 degrees Celsius, one speaks of fever. Fever describes an increase in body temperature caused by the organism, which supports the body's own healing process as a defense reaction.
  • Concomitant symptoms: Excessive sweating, thirst, glassy eyes, dry skin, coated tongue, chills, loss of appetite, nausea and vomiting, constipation, faster breathing, inner restlessness, confusion, impaired consciousness, sometimes febrile seizures in children.
  • causes: Since fever is one of the body's defense reactions, numerous symptoms can trigger the symptom, for example: infectious diseases, inflammation, poisoning, reaction to medicines, tumor diseases, rheumatological and chronic diseases, hormonal disorders, allergies, thromboses, heat strikes, hepatitis and many more.
  • Therapies: In adults, fever below 39 degrees Celsius does not necessarily have to be treated. If the body temperature rises further, hand-warm calf wraps or antipyretic medication can be used. Further therapeutic measures are based on the medical diagnosis.
  • Naturopathy: In addition to the tried and tested calf wraps, homeopathic remedies such as aconite, belladonna, ferrum phosphoricum, Gelsemium and Schüßler salts are used. Medicinal plants are chamomile, coltsfoot, elder and ribwort.

When should you go to the doctor with a fever?

In many cases, a body temperature of up to 39 degrees Celsius in adults does not need to be treated by a doctor. On the contrary: The elevated temperature helps the body to fight the responsible pathogens. But when does a fever need to see a doctor? Children are given different recommendations here than adults. The following guidelines are recommended by the Federal Center for Health Education (BzgA) and the Professional Association of German Internists (BDI) and are a general rule of thumb when a doctor should be consulted for fever:

  • In infants (0 to 3 months): When a newborn has a body temperature above 38 degrees Celsius. Even beforehand, when it looks limp overall, no longer wants to drink or skin discolouration occurs.
  • Infants up to two years old: If the fever - measured in the buttocks - is over 39 degrees Celsius and lasts longer than two days.
  • Younger children over 2 years: If the fever - measured in the buttocks - is over 39 degrees Celsius and lasts longer than three days. If there is no improvement despite antipyretic measures. When additional symptoms such as headache, diarrhea, vomiting, abdominal pain, rashes, shortness of breath or a stiff neck appear.
  • With all children: With indifference, abnormal reactions, persistent exhaustion despite falling body temperature, when the child does not want to drink, when febrile seizures appear or when there is concern for the child's well-being for some reason.
  • In adults: If fever persists above 39 degrees Celsius for three days, if it occurs repeatedly, if the fever rises above 40 degrees Celsius, if you feel very weak or if other symptoms appear.
  • Important: If in doubt, you should always listen to your own gut feeling and see a doctor as soon as you feel you need one.

What happens in the body when there is a fever?

The body has numerous possibilities to raise its temperature or to keep it better. For example, the heat dissipation can be reduced by reducing blood flow or contracting the blood vessels in the skin. The extremities may also be less supplied with blood in order to stabilize the core body temperature. However, what is more important with regard to fever is the acceleration of the metabolism, which leads to an increase in body temperature. This manifests itself, for example, in an increased heartbeat rate. The frequency per degree Celsius of the temperature rise increases by around ten heartbeats per minute. High temperatures can therefore be associated with a real racing heart. The breathing rate also increases noticeably as the metabolism accelerates. Another extreme form of the body's own heat production is rhythmic muscle contraction, known as chills.

Different methods for fever measurement

First of all, a body temperature is usually measured with the help of a clinical thermometer, whereby different parts of the body are particularly well suited for a temperature measurement. For example, the body temperature can be read under the tongue (sublingual), in the anus (rectal), in the ear (auricular) or in the armpit (axillary). The most precise results in relation to the actual body core temperature are provided by the rectal measurement, but it is also relatively cumbersome compared to the auricular measurement. Because the temperature in the ear can be read using an ear thermometer within less than ten seconds, while the rectal measurement usually takes significantly longer and is perceived as unpleasant by many patients.

What should be considered when measuring fever?

The deviations between measurements at different parts of the body can amount to up to half a degree Celsius. If a temperature above 38 degrees Celsius is determined during rectal measurement, this is considered a fever. A temperature above 41.1 degrees Celsius (measured rectally) falls under the medical name hyperpyrexia. Since the body temperature naturally varies during the day, several measurements should ideally be carried out at intervals. It should be borne in mind that the body temperature is significantly lower at night than during the day, that physical exertion can lead to a temperature rise of up to two degrees Celsius and that the body temperature reaches its highest level in the afternoon. In addition, women show fluctuations in body temperature of around half a degree Celsius depending on their menstrual cycle.

Concomitant symptoms

The shift in temperature regulation often leads to further symptoms in fever patients. The reduced blood flow to the extremities can lead to cold feet and hands. The skin sometimes appears marbled bluish due to the reduced blood flow. If pressure is briefly applied to the skin with the finger, it takes around two seconds before the whitish impression disappears. Here, doctors speak of a reduced capillary refill. Other general accompanying symptoms that can occur regardless of the underlying disease are:

  • Loss of appetite,
  • A headache,
  • Body aches,
  • Fatigue,
  • Impairment due to a lack of fluids (dehydration) when not drinking enough,
  • Sweating,
  • dry and hot skin,
  • shining eyes,
  • Tongue covering,
  • Chills,
  • Nausea and vomiting,
  • Constipation,
  • inner unrest,
  • Confusion,
  • Impaired consciousness.

Different forms of fever

Fever can occur in the form of recurring temperature peaks during the day (intermittent fever), persist over a longer period of time or as a type of fever that lasts for a few days, disappears and then recurs (alternating fever). The so-called double-peak fever, in which after a temporary increase in body temperature there is a drop in temperature for a few days and then an even more drastic increase in body temperature, is typical evidence of a viral disease. Children up to the age of six may experience so-called febrile convulsions on the train of the fever, which are associated with a loss of consciousness and sudden muscle cramps - similar to an epileptic attack.

Special forms of fever

Ultimately, numerous other special forms of fever can be identified, which are not infrequently named after their conspicuous accompanying symptoms, such as the so-called typhus fever (fever accompanied by an itchy rash) or hemorrhagic fever (fever accompanied by bleeding). Other forms of fever are named according to their triggers, such as o'nyong nyong fever or dengue fever, each caused by a virus of the same name.

High fever can be dangerous

If a body temperature of over 40 degrees Celsius is reached, this can be quite dangerous, especially for adults. Children, however, are more likely to show such a high fever without further health effects from the rise in temperature. But in adults, a body temperature above 40 degrees Celsius is usually a sign of an extremely serious infection. Due to the self-regulation of the organism using various hormones, neurotransmitters and certain other messenger substances, the body temperature rarely rises above 41 degrees Celsius. However, if this limit is exceeded, the cell proteins threaten to denature and the organism reacts with the so-called heat shock response to protect itself. If the temperature rises further, the affected patients run the risk of potentially fatal cardiovascular failure.

How does fever help the body?

The support function in combating pathogens is also based in part on the mechanism of the heat shock response, but primarily in the direction of the pathogen. For example, bacteria respond with a heat shock response to the rise in temperature, which in turn makes it easier for the immune system to fight the intruders. The processes involved are extremely complex and have not yet been conclusively clarified. What is certain, however, is that fever promotes healing and, in the worst case, antipyretic measures can even have a counterproductive effect.


Viral and bacterial infections are particularly common causes of fever. Here, the possible triggers range from flu viruses and bacteria, such as streptococci and pneumococci, to exotic pathogens such as the dengue virus or the unicellular parasites from the genus Plasmodium, which cause malaria. In addition, other types of inflammatory reactions in the organism, such as vascular inflammation (vasculitis), also sometimes lead to a fever. Furthermore, certain tumors (for example, Hodgkin's disease) can trigger an increase in body temperature. Trauma injuries, such as after an accident, are also occasionally associated with fever.

Common fever causes in children

The most common fever-causing infectious diseases in Germany include, for example, the typical childhood diseases such as measles, rubella and chickenpox. Pseudo croup, which describes a mostly viral inflammation of the upper respiratory tract, which is associated with cough, hoarseness and shortness of breath, should also be considered as a possible cause of the fever in infants and young children. Cough associated with persistent elevated body temperatures should be a reason to visit a doctor in both children and adults, as pneumonia could be behind the symptoms.

Common fever causes in adults

Infectious diseases common to adults that cause fever include flu infections, influenza, tonsillitis, wheezy glandular fever and classic gastrointestinal infections caused by viruses (e.g. rotaviruses or noroviruses), bacteria (e.g. Salmonella, Escherichia coli or Campylobacter) and in rare cases by so-called protozoa (single cells such as amoebas). Inflammation of the kidney pelvis can also be mentioned as a more common cause of the increased body temperature. More serious underlying diseases, which fortunately occur less frequently, are the potentially life-threatening meningitis and myocardial inflammation.

Rheumatic fever

A special form of bacterial fever is the so-called rheumatic fever (reactive arthritis), caused by a streptococcal infection or the result of such an infection. Streptococci in themselves lead to infectious diseases such as scarlet fever, tonsillitis or otitis media. After the actual infection, the antibodies formed can turn against your own body and cause damage to the connective tissue, organs, joints, nervous system or brain.

Rheumatic fever is part of this process. Weeks after the actual infection, those affected suffer from high body temperatures as well as swollen, overheated and painful joints. Symptoms similar to rheumatic fever sometimes lead to a gout attack, whereby gout is based on a malfunction of the metabolism, which leads to the deposition of uric acid crystals in the joints. In an acute attack of gout, the fever is the result of the ongoing inflammatory processes.

Fever from poisoning

Poisoning, for example from fungal toxins, can also be accompanied by fever. In principle, the so-called polymer fever, which is caused by the toxic decomposition products of Teflon, can also be assigned to the poisoning. Excessive heating of the Teflon leads to breakdown into toxic fluorine compounds, which cause flu-like symptoms when inhaled. Furthermore, drugs or their side effects can also cause fever. The symptoms usually appear around a week after taking the medication. Drug fever is known, for example, for numerous antibiotics, antifungals (medicines for fungal infections) and chemotherapy drugs. In theory, however, a corresponding response from the organism can occur with almost all medicinal products.

Autoimmune and inherited diseases

In rare cases, fever can also be observed in the context of autoimmune diseases such as collagenosis, which affects the connective tissue and blood vessels. The fever can also be due to an inherited disease. These so-called inheritable fever syndromes include familial Mediterranean fever (FMF), hyper-IgD syndrome (HIDS) and so-called tumor necrosis factor receptor 1-associated periodic syndrome (TRAPS). As a common feature, the fever syndromes have recurrent fever phases, which are associated with signs of inflammation in the blood.

Fever of unknown cause

If the fever occurs without obvious causes, it lasts more than three weeks with measured temperatures above 38.3 degrees Celsius and the standard treatments are unsuccessful, doctors speak of a fever of unknown cause. This fever is often based on undetected infections, tumor diseases or rheumatic diseases. Fever with unknown causes is divided into four different types:

  • Classic fever of unknown cause,
  • Nosocomial fever of unknown cause,
  • Neutropenic fever of unknown cause,
  • Fever of unknown cause in people with HIV.

Classic fever of unknown cause

This type of fever is characterized by a fever lasting more than three weeks. Infections, malignant tumors or connective tissue diseases such as rheumatic diseases or collagenosis are often responsible. Diseases of the blood vessels are also conceivable.

Nosocomial fever of unknown cause

This category includes patients who develop a long-lasting fever after hospitalization. Common causes are pulmonary embolism, intestinal infections with the bacterium Clostridium difficile or phlebitis, in which the germs have spread through the bloodstream. In addition, reactions to medication can be considered. Patients who develop nasal inflammation (sinusitis) as a result of nasogastric tube feeding can also develop such a fever.

Neutropenic fever of unknown cause

This type of fever can occur in people who have too few white blood cells in their blood. Specifically: Show fewer than 500 neutrophil granulocytes per cubic millimeter of blood. Bacteria, fungi or viruses are often responsible for this symptom. A typical feature of this type of fever is that in many cases the organs are not infected. Instead, the pathogens are found in the blood, with no apparent cause as to how they got there.

Fever of unknown cause in people with HIV

This type of fever occurs in connection with an acute or existing HIV virus infection. This is mostly caused by pathogens that usually do not cause disease in healthy people (e.g. cytomegalovirus, Pneumocystis jeroveci, Mycobacterium avium-intracellulare). Rare tumors such as Kaposi's sarcoma or lymph gland cancer can also be responsible for this fever.


Given the multitude of causes that can cause fever, the diagnosis can be extremely difficult, especially if there are no other accompanying symptoms to help diagnose it. After a thorough medical history, various examinations are carried out to narrow down the cause of the fever.

What does the doctor?

Once the temperature increase has been clearly determined, further examinations follow to determine the cause of the fever. These range from a physical examination with wiretapping and palpation of possibly diseased organs to the taking of blood samples up to examinations using imaging methods such as ultrasound, computer tomography or magnetic resonance tomography.

Many causes are identified in the laboratory

Blood tests in particular often play a special role in determining the triggers. Under certain circumstances, the pathogens can be identified directly in the course of a microscopic analysis of the blood, can be bred from the blood, leave traces of their genetic material in the blood or can be detected using the respective antibodies. Laboratory tests of urine can also provide important information about the causes. Endoscopic examinations (for example gastroscopy, colonoscopy) may be provided as further diagnostic methods. In case of doubt, a tissue sample (biopsy) can also be taken.

Accompanying symptoms provide clues to the cause

Based on the duration, there may be additional indications of the cause of the increased body temperature. After a day or two of fever, it is usually not possible to make a statement about the possible triggers, but the longer the fever persists, the more reliable conclusions can be drawn from the evaluation of the so-called fever curve. In addition, after a few days there are usually typical accompanying symptoms, which enable very precise diagnoses even without a more extensive examination. Ultimately, the duration of the fever and the accompanying symptoms provide decisive information about the diagnosis. Here are a few examples:

  • Sore throat: Typical indication of tonsillitis.
  • skin rash: If skin rashes appear from the fourth day of fever, it could be a measles disease.
  • Stiff neck: A stiff neck in combination with fever is a warning sign of possible meningitis.
  • Chest pain: If fever patients suffer from chest pain or heartache, this may be due to an inflammation of the heart.

Medical Definition - What is Fever?

Fever describes an increase in body temperature caused by the organism. This is triggered in the so-called heat regulation center of the brain and is a defense reaction of the body. Fever is not an independent disease, but a symptom that the body uses in response to the underlying cause. Doctors only speak of fever when a rectally measured temperature of 38.2 degrees Celsius is reached. Even under normal conditions, body heat is affected by fluctuations. This counts for the individual body regions as well as for the course of the day. Armpit measurements are considered inaccurate and should be avoided if possible. From a temperature of more than 40 degrees Celsius, the high body temperature in adults can be dangerous - from 42.6 degrees Celsius it is usually fatal.

Do not confuse:

Fever should not be confused with increased body temperature due to external heat or an overheating of the organism during physical exertion. Here, the body temperature also appears to be increased, but the setpoint of the body temperature is unchanged.

How does the body trigger a fever?

Fever refers to a relatively wide range of increased body temperatures, although the consequences for the organism can vary widely. The basis of the fever is an increase in the target value of the body temperature in the center of the temperature regulation in the brain (more precisely: in the hypothalamus). Certain endogenous messengers, the so-called endogenous pyrogens, play an important role here. These lead to a shift in the regulatory balance of body temperature. In interaction with other hormones or messenger substances, the pyrogens inhibit heat sensitivity in the brain, which stimulates the body to generate more heat. The actual temperature is perceived lower than it is, and the organism tries to counteract it.
[GList slug = ”10 home remedies for fever”]


Fever is a natural defense reaction of the organism, which actually does not require any treatment. Rather, the cause of the increased body temperature should be determined and treated. To this day, however, it is quite common in medical practice to use antipyretic measures when a critical core body temperature is exceeded (around 40 degrees Celsius in adults), although it is known that the reduction may slow down the healing process or prolong the disease.

If the core body temperature reaches values ​​above 41 degrees Celsius, however, the impending health impairments may be more serious than an extension of the course of the disease. In addition to the treatment of the underlying disease, the immediate treatment of the fever can also make sense here.

Medicines for fever

Numerous medications, so-called antipyretics such as acetylsalicylic acid, ibuprofen or paracetamol, are available to lower the body temperature. So-called fever suppositories are administered more often, especially in children. Willow bark is also used as an active ingredient in naturopathy. The salicin contained has an antipyretic effect in the organism.

Non-drug measures

In addition to the medicinal approaches to lowering the fever, various accompanying measures, such as calf wraps, are recommended to help dissipate heat. If the body temperature is extremely high, cooling with ice packs can also be used for emergency care. By resting in the groin area, the body core temperature is quickly lowered. Accompanying patients should generally pay attention to the fluid intake, since their fluid requirement is significantly increased.

The cause determines the appropriate therapy

The selection of the appropriate antipyretic treatment is also to be seen depending on the causes of the disease, for example, against life-threatening blood poisoning (sepsis) with other means than against less dangerous infections. It is also important to check whether the antipyretic therapy is necessary at all. For example, lowering the level of medication in case of a rather harmless runny nose or a cold (flu infection) usually makes no sense.

Bed rest with fever?

Those affected are generally advised not to expose themselves to any particular physical stress. However, bed rest is only required for certain clinical pictures. If the fever goes down, the body releases more heat through the skin in order to reach the now lower setpoint of the body core temperature. The superficial blood vessels widen, the skin appears reddened and those affected start to sweat more.


As discussed in the previous sections, fever is part of the immune response to different threats. The defense strategy has prevailed in evolution over thousands of years and can also be observed in most animals. Their meaning is therefore out of the question and treatment is generally not required from a naturopathic point of view. Here too, however, the restriction mentioned above applies that lowering the fever can make sense if there are impending serious consequences of the increased body temperature. If the patient feels extremely uncomfortable and weakened, a therapeutic lowering of the fever should also be considered under consideration of a possible delay in the course of the disease.

Naturopathic support for fever diseases

Naturopathy also uses homeopathic remedies (e.g. aconite, belladonna, ferrum phosphoricum, gelsemium) and Schuessler salts (no. 3 Ferrum phosphoricum, no. 5 potassium phosphoricum) - in addition to the previously mentioned home remedies for fever (calf wraps, ice water bags), to lower body temperature. Furthermore, there are various medicinal plants or herbal active ingredients for lowering fever and treating the causes of the fever. Examples include chamomile flowers, the leaves of coltsfoot, extracts of elderflower and ribwort herb. Orthomolecular medicine (OM), in which high-dose vitamins are said to alleviate symptoms, is sometimes used to treat fever in naturopathic therapy. Basically, however, natural medicine - like conventional medicine - is less about fever than about its causes. (fp, vb; updated on October 9, 2018)

Author and source information

This text corresponds to the specifications of the medical literature, medical guidelines and current studies and has been checked by medical doctors.

Dipl. Geogr. Fabian Peters


  • Michael Weiß et al .: "My child has a fever", German Society for Pediatric and Adolescent Medicine e. V. (DGKJ), (accessed August 13, 2019), DGKJ
  • Internists on the net: What is fever?, Professional Association of German Internists e.V., (accessed August 13, 2019), BDI
  • Pediatricians online: Fieber, professional association of pediatricians e. (BVKJ), (accessed August 13, 2019), BVKJ
  • WJ Heinz et al .: Diagnosis and empirical treatment of fever of unknown origin (FUO) in adult neutropenic patients: guidelines of the Infectious Diseases Working Party (AGIHO) of the German Society of Hematology and Medical Oncology (DGHO), (accessed August 13. 2019), PubMed
  • Federal Center for Health Education (BZgA): Fever in babies and children, (accessed August 13, 2019), BZgA
  • Allan R. Tunkel: Fever in Adults, MSD Manual, (accessed August 13, 2019), MSD

ICD codes for this disease: R50ICD codes are internationally valid encodings for medical diagnoses. You can find e.g. in doctor's letters or on disability certificates.

Video: Fever in Adults The Urgency Room an educational care video (July 2022).


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