Fever is a very common non-specific symptom of many diseases. Often the increased body temperature is due to an infection, which can be quickly corrected. Sometimes, however, fever may also occur in serious illnesses, e.g. B. occur in malignant tumors, as a symptom.
– Dr. Tobias Weigl
Reviewed by medical experts and written according to the best scientific standards
This text has been prepared in accordance with medical literature, current guidelines and studies, and has been reviewed by a medical professional prior to publication.
In this video Dr. Tobias Weigl "What fever is", "How fever develops" and also "How to reduce fever".
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What is fever? How does the heat regulation in our body work??
So fever is not a disease, but a symptom. One could also call fever a natural protective reaction of our body against pathogens and infections. Because by raising the body temperature, the body mobilizes its defenses and acts independently against pathogens. This is because these same pathogens, mostly viruses or bacteria, multiply worse at an elevated temperature than at normal. However, particularly high fevers can severely restrict certain bodily functions and are in any case a great strain on our organism.
But what is considered too high or elevated? The following table can help to understand the individual temperatures as well as their classification.
Fever classification
| 36,5 – 37,4 °C | Normal temperature |
| 37,5 – 38,0 °C | Subfebrile temperature |
| 38,1 – 38,5°C | Light fever |
| 38,6 – 39,0 °C | Moderate fever |
| 39,1 – 39,9 °C | High fever |
| 40,0 – 42,0 °C | Very high fever |
The hypothalamus, a part of our diencephalon, is responsible for regulating body temperature. It is responsible for keeping the temperature in the heart, kidneys, brain and liver as constant as possible, and controls the production and release of heat for this purpose. As a rule, the target temperature is around 37°C.
If there is now an infection or another form of inflammation in the body, the target value changes upwards, so that the hypothalamus makes an adjustment and the body finally heats up.
How the body regulates its temperature
This happens by increasing the metabolism or by additional muscle work. Depending on the severity of the infection, this can lead to the well-known chills. In addition, the body lowers the release of heat by contracting blood vessels in the periphery, that is, the area away from the center of the body. Less heat escapes through the skin.
Substances that increase the set point of body temperature are called Pyrogens called fever (from gr. pyros Fire’ and gr. gennan ‘produce’). They can be caused not only by external factors (e.g. as components of viruses or bacteria) find their way into the body. They can also arise in the body, as a reaction to an infection. Certain bacteria or viruses can stimulate immune cells to produce the substances that trigger the fever.
The three stages of fever
From a medical perspective, fever is divided into the following three stages:
- Fever increment (so called. ‘Stage increment‘): Adults react with chills at this stage. In susceptible infants or young children, a febrile convulsion may occur during this stage, which hardly exceeds a duration of 15 minutes. Older children get chilly limbs, shivering and circulatory centralization occurs. The latter describes the restriction of blood flow to the vascular areas distant from the center of the body, e.g., the vasculature. Muscles, skin or kidneys. On the other hand, the blood flow to the brain and heart improves.
- Fever height (so called. ‘Fastigium‘): High fever is associated with the risk of so-called febrile delirium (from lat. delirare ‘to be insane’) accompanied by. This type of delirium occurs mainly during prolonged high body temperatures and is characterized by clouding of consciousness, delusions, hallucinations, anxious agitation and motor restlessness.
- Drop in fever (sog. ‘Stage decrementi‘): In this stage the fever disappears, either slowly over several days or rapidly over a period of hours. Typical for this stage are sweating and loss of fluids, and possibly circulatory dysregulation if the fever is broken too quickly.
The different courses of fever
For the sake of completeness, the various forms of fever should be briefly mentioned at this point. In the past much importance was attached to these. However, due to the therapeutic measures available and regularly used today, the different forms of progression are only rarely observed.
Forms of the course of the fever
| Continua febris | Temperature over several days above 39 °C, fluctuations less than 1 °C | Epidemic spotted fever, brucellosis |
| Relapsing fever | Stronger fluctuations, always above normal temperature | sinusitis (sog. ‘sinusitis’), urinary tract infections |
| Intermittent fever | High temperatures and fever-free periods alternating during the course of a day, fluctuations of more than 1.5 °C | Blood poisoning (so called. ‘sepsis’), pleurisy (sog. ‘pleurisy’) |
| Recurrent fever | Fever episodes over several days alternating with 2-15 days of absence of fever | Malaria, Lyme disease, cholecystitis (sog. ‘cholecystitis’) |
| Undulant fever | Temperature course is wave-like, phases with high fever and fever-free intervals over several days | Hodgkin’s disease, tumors |
| Biphasic fever | Curve with two peaks, similar to the humps of a camel | measles, meningococcal sepsis |
The causes of fever
Now that the physical processes involved in fever have been clarified, we can turn our attention to its causes. However, these are so numerous and varied that a list of the possible underlying diseases would go beyond the scope of this article. In the following some illnesses are therefore listed, which are accompanied by fever as a non-specific general symptom and belong to the more frequent Causes include.
Infections caused by bacteria, viruses and fungi
As already mentioned at the beginning, fever is a response of our body to infections as well as their pathogens. The body tries to get rid of pathogens by raising the temperature, thus remodeling the environment in which pathogens normally thrive best – at normal body temperature. Thus go bspw. typical respiratory infections, such as a cold or bronchitis, are accompanied by a mild fever and headache, while the true flu (so-called "cold") is accompanied by a mild fever and headache. ‘Influenza‘) especially suddenly begins with high fever as well as sore throat.
Malignant diseases
In medicine, malignant generally refers to diseases that progress in their development in such a way that they have a devastating effect on the entire organism. Especially in the field of oncology – the science that deals with cancer – the term has become established. In this context, fever is a fairly common symptom of malignant diseases and can occur as an initial symptom, but also only after chemotherapy has been administered.
Trauma
Trauma is the medical term for physical damage caused by external influences, as a result of which tissue structures are destroyed or restricted. Examples are bruises (so called. ‘Hematome‘) or bone fractures (sog. ‘Fractures‘). The latter are more often accompanied by fever, especially in children.
Autoimmune diseases
Autoimmune diseases are all diseases in which the immune system attacks the body’s own structures. Fever is then often considered the first sign.
To the less frequent possible causes include u. a.:
Neuroendocrine disorders
Neuroendocrine disorders are roughly disorders that affect the secretion of messenger substances from the nervous tissue. This includes z. B. the hyperthyroidism (so called. ‘Hyperthyroidism‘). A possible complication that can arise from this interference is the so called "hard drive". Thyrotoxic crisis. This is accompanied by a high fever.
Dehydration
In the case of dehydration, i.e. the insufficient supply of water to the body, the so-called thirst fever can occur, mainly in infancy. This arises as a result of too little water or. with an excess of salt in the body. The latter occurs mainly as a so-called saline hyperthermia after too much salt intake or. to severe water loss. The fever is usually higher in the morning than in the evening because of the nocturnal drinking break.
Autoinflammatory diseases
These diseases are inflammatory reactions that seem to occur on their own and are not triggered by any pathogens. Responsible for the occurrence is the immune system, which triggers inflammatory reactions as a defense mechanism, although no pathogens are present.
An example of an autoinflammatory disorder is the Familial Mediterranean fever, which is more common in the eastern Mediterranean region. This is a hereditary condition that is usually diagnosed before the age of 30. Age of life begins. One speaks also of a periodic fever syndrome, since the illness is characterized by recurring fever attacks as well as pain.
fever as a result of drug or medicine consumption
A fever can also be the result of medication or drug consumption. The way in which the fever develops is then varied. It results either as anaphylactic shock as a result of an allergic reaction, is the result of a congenital hypersensitivity (so-called. ‘Ideosyncrasy‘), a substance-related or pharmacological reaction, or occurs due to a change in thermoregulation.
The resulting ‘drug fever’ is difficult to predict. While allergic reactions can cause a temperature rise after only hours of ingestion, bspw. antibiotics do not produce fever until after about 5-6 days. Drugs that affect the heart and blood vessels sometimes cause a rise in temperature only after 45 days. The list of agents that cause fever is long and includes penicillins or cephalosporins.
Among drugs, the amphetamine derivative MDMA, better known as ecstasy, should be mentioned in particular at this point. This intoxicating drug can cause massive hyperthermia by decreasing heat dissipation, constricting skin vessels, and increasing heat production. As a result, the body’s own protein coagulates, causing irreversible, i.e irreversible causes muscle damage.
Diseases of the central nervous system (CNS) affecting the heat center
This occurs e.g. in the case of craniocerebral injuries, as a result of which a so-called Central fever may occur. This fever occurs when the thermoregulatory center is damaged. Often, antipyretic agents do not have any effect in this context.
Fever of unclear origin (FUO)
Last but not least, the so-called Fever of unclear cause (short: FUO, from engl. ‘fever of unknown origin’) to mention. This is present when a temperature of more than 38 °C (38.5 °C in children) is measured over a period of at least 8 days without a cause being identified. Because even with today’s diagnostic standards, a cause for the fever cannot always be determined.
Video excursion: Hyperthyroidism
In the case of hyperthyroidism (so called. ‘Hyperthyroidism’), a so-called thyrotoxic crisis can occur as a complication, which u. a. accompanied by fever. But what exactly is hyperthyroidism?? Why do you get one of these and what other symptoms indicate a disease?? These and other questions are answered by pain therapist Dr. Tobias Weigl in the following contribution and discusses in addition the special form with the name Graves’ disease, with which it concerns an autoimmune disease.
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Symptoms: What are the symptoms of fever??
With fever first naturally a temperature increase above the target value before. However, it often goes with more Associated symptoms accompanied by. These include:
- General feeling of illness
- Loss of appetite
- Joint and limb pain
- Bright light and loud noises are perceived as unpleasant
- Feeling of thirst
- Sweating
- Shiny eyes
- Dry and clogged tongue
Complications, which can arise with fever are meanwhile:
- Increased heart rate (sog. ‘Tachycardia‘)
- Accelerated respiration (so-called. ‘Tachypnea‘)
- Circulatory dysregulation including dizziness, lightheadedness, unconsciousness, pallor, sweating, nausea and ringing in the ears
- Decrease of blood pressure (so called. ‘Hypotension‘)
- Epileptic seizures
Survey: Causes of fever
Progressive forms of fever
| Continua febris | Temperature above 39 °C for several days, fluctuations less than 1 °C | Epidemic spotted fever, brucellosis |
| Relapsing fever | Stronger fluctuations, always above the normal temperature | Sinusitis (so called ‘pleurisy’). ‘sinusitis’), urinary tract infections |
| Intermittent fever | High temperatures and fever-free phases alternating in the course of a day, fluctuations of more than 1.5 °C | Blood poisoning (so called. ‘sepsis’), pleurisy (so-called. ‘pleurisy’) |
| Recurrent fever | Fever episodes over several days alternating with 2-15 days without fever | Malaria, Lyme disease, gall bladder inflammation (sog. ‘cholecystitis’) |
| Undulant fever | Temperature course in waves, phases with high fever and fever-free intervals over several days | Hodgkin’s disease, tumors |
| Biphasic fever | Progressive curve with two peaks, similar to the humps of a camel | Measles, meningococcal sepsis |
What does the doctor do? Part 1: Diagnosis
Patients with fever are first questioned in detail in the so-called anamnesis conversation, i.e. the conversation between doctor and patient. The time and the circumstances under which the fever became noticeable will be discussed. If it occurred at home or during a hospital stay?
Furthermore, the question about a stay abroad, especially in the tropics, is especially important. The fever could be the result of an illness resulting from contact with other people or animals, or the consequence of an insect bite or animal bite. In this context the doctor will also inquire about the vaccination status. Furthermore, medications taken that may have triggered the fever are asked about. Other accompanying symptoms are also discussed.
If, in addition to the fever, a patient suffers from z. B. If the patient also has chills, this already allows conclusions to be drawn about the cause of the fever. For chills can cause u. a. associated with blood poisoning (so-called. ‘SepsisThe following conditions can be treated with antibiotics: a bacterial infection of the heart valves, a bacterial pneumonia, meningococcal meningitis, erysipelas, malaria, inflammation of the renal pelvis, Weil’s disease, and allergic reactions to medicines. a.
Different examinations provide clarity about the cause
The next step is physical examination, during which the doctor will take a closer look at the throat, nose and ears. If a rash is present, he will also inspect the skin more closely. He will also palpate the lymph nodes in the neck and listen to the heart and lungs with a stethoscope. Last but not least, an examination of the abdomen and a palpation of the kidneys are then performed.
Often, the steps taken up to this point do not yet allow a definite diagnosis, which is why Laboratory tests be carried out. This can help z. B. A rapid urine test can detect bacteria that cause a urinary tract infection, which in turn can be responsible for the fever. In addition, the blood can also be examined. From this, the doctor takes liver and kidney values, electrolytes, proteins, coagulation values, antibody formation, etc., which can support the diagnosis.
If this step also does not allow conclusions to be drawn about the cause of the fever, doctors have many other methods at their disposal to determine any triggering factors. These include u. a. a tuberculosis test, an ultrasound of the heart and abdomen, an X-ray of the lungs, stool samples, CT (computer tomography) and MRI (magnetic resonance imaging), endoscopic examinations and many more.
Fact Box
Fever
- Subdivision into six classes, from normal temperature (36.5 – 37.4 °C) to very high fever (40.0 – 42.0 °C)
- Fever generally progresses in three stages: fever rise, fever height and fever fall
- Causes are varied; from infections to malignant diseases (z. B. cancer) to autoimmune diseases
Symptom
- Temperature rise above target value
Accompanying symptoms
- General feeling of illness
- Loss of appetite
- joint and limb pain
- Bright light and loud noises are perceived as unpleasant
- Feeling of thirst
- Sweating
- Shiny eyes
- Dry and clogged tongue
What the doctor does? Part 2: Treatment
In general, fever is treated less for the symptom itself than for the actual symptoms fever-inducing underlying disease. This means that bspw. a bacterial infection is treated with antibiotics, which usually reduces the fever.
It becomes problematic when it is not known what caused the fever, i.e., a fever of unclear origin (FUO for short) is present. Does the physician take in this connection bspw. indicate that the fever may be caused by a. If a patient’s condition can be traced back to a reaction to medication, he will first arrange for all non-essential medication to be discontinued. Afterwards, of course, he will continue to examine and question you in detail. Additional laboratory tests may also be required. The focus of treatment is then on the most probable cause.
What can I do myself?
Symptomatic treatment of fever is possible, but not always necessary. As mentioned at the outset, a fever is basically the body’s own defensive reaction, directed against any pathogens. In general, it can be said that a fever up to 39 °C against this background does not actually require any treatment. If the measured temperature is between 39°C and 40°C, you can try to control the fever on your own with paracetamol or calf wraps.
Last but not least, always make sure that the body is given enough fluids. Because the need is increased when there is a fever. A rule of thumb is: for every degree of temperature rise above normal (approx. 37 °C), the body needs about 0.5-1 liters of water per day in addition to the normal recommended drinking amount of 1.5-2.5 liters.
Frequent patient questions
My child has a fever – When should I go to the doctor??
Dr. T. WeiglIn general, a doctor should be consulted when the temperature reaches 39°C. In about 90 percent of cases, this can identify the cause and treat accordingly. A visit to the doctor is also recommended if the fever lasts longer than a day, if it persists despite suppositories and calf wraps, or if there are accompanying symptoms such as diarrhea, abdominal pain, vomiting or skin rash, febrile convulsions, and persistent impairment despite fever-reducing measures.
What is anaphylactic shock??
Dr. T. WeiglAnaphylactic shock is a sudden allergic reaction that, although rare, can cause multiple organ systems to collapse and can be life-threatening. Every year, about 1-3 out of 1 million people die from anaphylactic shock. The term shock is used in this context because it is the extreme form of an anaphylactic reaction, which is usually accompanied by sudden allergy symptoms and affects several organs.
The most common triggers of such a reaction are foods, insect bites and medications. The symptoms include reddening of the skin, itching and swelling of the mouth and throat in almost 90 percent of cases. In addition, skin irritation, breathing difficulties, disturbances of the cardiovascular and digestive systems and a significant drop in blood pressure may occur. Since allergic emergencies of this kind also occur more frequently in a clinical facility, these are equipped with appropriate emergency kits. If a shock occurs outside such a facility, a supply of the allergen should be stopped in emergencies. This means, for example, removing a bee sting or stopping the administration of medication.
The most important drug that is then used is adrenaline. Because this reduces discomfort to the heart, skin and respiratory tract. Patients with an emergency kit should ideally always have an emergency kit on hand, which u. a. Adrenalin for self-injection, an antihistamine as well as a glucocorticoid are included.
Emergency measures in the event of anaphylactic shock
Among the important immediate relief measures for anaphylactic shock:
- Keep calm and do not leave the affected person alone
- Apply emergency kit (if available)
- Make an emergency call to 112
- Position the affected person correctly (in case of dizziness, head and upper body flat and legs elevated; in case of respiratory distress, sitting; in case of unconsciousness, stable lateral position)
- Cool swellings
- Keep airways clear
What exactly is paracetamol?
Dr. T. WeiglParacetamol is a classic painkiller, antipyretic and flu medication and therefore plays an important role in colds, flu and fever. It is used in the context of pain therapy, especially for pain in the joints, legs, lower back, knees. It has hardly any negative effects on the gastrointestinal tract, but unlike the painkillers ibuprofen or diclofenac, it also has no anti-inflammatory (so-called. ‘Antiphlogistic‘) Effect. Nevertheless, the same applies here: No effect without side effect. For prolonged use can cause kidney damage in rare cases and an overdose can bring liver damage with it.
For more information on acetaminophen, see my post below, in which I address the drug and discuss side effects and incorrect dosages.
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