Fever - What the Symptom Means

38 degrees Celsius or more on the clinical thermometer indicates a fever. Mostly, but not always, infections are to blame. Sometimes the trigger remains unclear. More about causes, diagnosis, therapy

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In principle, a fever is a sensible response from the body

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Fever: Generally useful

Fever has many causes. As a typical symptom of an infection, it often signals that the immune system is currently increasingly dealing with a pathogen or inflammatory factor. In the process, the body produces a large number of antibodies.

Some of these, called pyrogens, cause a fever. Important defense reactions are accelerated at higher temperatures. In this respect, fever is, in principle, a sensible reaction of the body.

Fever - the most important things at a glance

  • Definition: A body temperature of 38.2 ° C * is considered a fever. There is often talk of fever from 38 ° C. If the fever persists for more than three weeks, but the cause is unknown, it is a fever of unknown origin.

    (* measured rectally (in the bottom))

    Body temperature - values ​​for orientation *

  • Normal: 36.5 ° C to 37.4 ° C (Children: 36.5 ° C to 37.5 ° C)
  • Elevated: 37.5 ° C to 38.1 ° C (Children: 37.6 ° C to 38.4 ° C)
  • Fever: over 38.2 ° C (children: from 38.5 ° C; infants <three months: from 38 ° C)
  • High fever: from 39 ° C
  • Extremely high fever (hyperpyrexia): over 40 ° C
  • When to the doctor The following applies to infants up to three months of age: if the body temperature is above 38 ° C, consult a pediatrician to be on the safe side. Parents should take a toddler under the age of two to the doctor if they have a fever for more than a day.

    Older children and adults should see and treat a doctor if the temperature is greater than 39 ° C or if the temperature lasts for more than two days or occurs repeatedly. How urgent the visit to the doctor is always depends on the individual case, on the symptoms and how you feel overall.

  • What to do? At temperatures above 39 ° C (there is no hard and fast rule) one can try to lower the fever for a short time, especially if it is very debilitating, with calf compresses or with the drug paracetamol.

    ! Important: Do not use calf compresses if you are cold or cold, or if your hands and feet are cold. Leave joints free. The temperature is allowed to drop by about one degree. More information in the section: "Fever - Tips and Therapy" below.

What body temperature is normal at all?

A normal body temperature - around 37 ° C inside the body - is the simple-sounding result of a complicated set of rules. The body's heat production and dissipation play a decisive role in this.

Within certain limits, he can keep his core temperature constant regardless of the ambient temperature. This is important for the constantly running metabolic processes.

You have to know: The heat regulation center in the brain works in a similar way to a thermostat. It controls body temperature around the clock. If certain factors adjust the setpoint of the thermostat, the body adjusts the temperature.

The normal body temperature is subject to a certain range. For one thing, it fluctuates over the course of the day. On the other hand, there are individual differences.

It is lowest in the second half of the night and in the morning, and highest in the evening. Physical work heats up, but so does a large meal or stress. Either way, we work up a lot of sweat, but the sweat pool cools us down again after a while.

In women of fertile age, the body temperature rises by around 0.5 ° C after ovulation in the middle of the cycle and remains at this level until the next menstrual period.

Some diseases show a typical temperature curve (examples)

© W & B / Felix Schneider


© W & B / Felix Schneider

Type of fever continuous: high, usually around 39 ° C or higher, slight fluctuations, often lasts for several days. Occurs, for example, with infections with various viruses.

© W & B / Felix Schneider

Intermittent fever type: the fluctuations are more than 1 ° C, the lowest temperature reaches normal values. Can occur, among other things, with tuberculosis. Often with tuberculosis there is only an increased body temperature, which can last longer than three weeks (according to the definition, an initially unclear fever).

© W & B / Felix Schneider

Periodic fever type, here: fever every three days: first day fever, two days fever-free, third day fever again. Characteristic of a (mostly mild) form of malaria called Tertiana.

© W & B / Felix Schneider

Periodic fever type, for example every fourth day: Such a fever curve indicates quartana malaria. Sometimes there is also a fever-free phase between the periods of fever.


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The inner glow: how does a fever develop?

Pathogens and inflammatory substances in the body can cause our internal thermostat in the brain to raise the setpoint of the body temperature. The body has several options for implementing this: It throttles the heat dissipation through the skin. Therefore it is initially dry, pale and cold.

At the same time it gives us the feeling of freezing and makes the muscles tremble. The chills increase heat production. We are happy to help and wrap ourselves up in warmth-giving textiles.

Even the liver becomes active by increasing the metabolism so that more internal heat is generated. Gradually the skin glows, the cheeks are red, the pulse and breathing pick up.

When defrosting is the order of the day, the skin gives off more heat again, it is reddened, damp or bathed in sweat. In addition, there is great thirst, especially if you have not consumed enough fluids beforehand. Even after the fever has passed, some may still feel weak or have little appetite for a while.

When is a fever dangerous?

A fever over 40 ° C is an emergency (call the doctor or an emergency doctor, emergency number: 112). One of the dangers of a high or persistent fever is dehydration due to lack of fluids - especially the very young and the elderly are at greater risk. Heart and circulatory problems and the risk of thrombosis (formation of a blood clot that blocks a vein in the leg) may increase.

In addition, there is a risk of dizziness and other disorders of the central nervous system, physical weakness, and the risk of collapse and falls. Conversely, there is also dehydration fever.

! Important: If you have a fever, drink enough fluids, half a liter to a liter more than usual.Healthy people should normally ingest 1.5 to two liters of fluid a day.

Infectious diseases, among others, are life-threatening and come under the term viral hemorrhagic fever, i.e. fever with bleeding. Various virus types that are not native to us are responsible, including the dreaded Ebola and Marburg viruses. Heat stroke is also dangerous.

A doctor should examine a child who has repeatedly had a fever

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Fever: when to see a doctor?

As I said: the temperature control is complicated, with babies it still has to settle in. On the one hand, they react more strongly to high ambient temperatures. On the other hand, very small babies - premature babies and newborns - often do not develop a fever at all when they have an infection. Small children and school children, on the other hand, quickly develop a fever.

For the little ones, the following applies: if the body temperature is 38 ° C or more, briefly consult the pediatrician to be on the safe side. But even if an infant is "only" noticeably sleepy or limp and drinks poorly, the doctor has to see what is going on.

The pediatrician or emergency doctor is also asked, for example, if a febrile child of any age vomits repeatedly, has diarrhea, marked stomach ache, headache, signs of shortness of breath or a febrile seizure.

Febrile seizures mainly occur between the ages of six months and five years. More on this in the chapter "in this post.

Older children and adults should be examined by a doctor if the temperature is above 39 ° C or if the fever lasts for more than two days (older children, adults). If the doctor cannot be reached, call the emergency doctor if the fever is high.

Accompanying signs of illness, their type and strength and how you feel overall are also decisive for whether and how urgently the doctor is asked.

This is urgent, for example, in the case of a skin rash accompanying the fever, it is necessary immediately in the case of neurological disorders such as drowsiness, clouding of consciousness or unconsciousness with (and without!) Fever or convulsions (see also below: Emergency, first aid, febrile convulsions in children).

If you have a fever after a stay abroad, you should also see a doctor immediately.

Main causes of fever

In addition to colds, other infectious diseases can trigger fever. Here is a selection:

  • Especially in children: Purulent tonsillitis caused by bacteria called streptococci or otitis media caused by pneumococci (Streptococcus pneumoniae), of course also the typical so-called childhood diseases and infections with Haemophilus influenzae type b (Hib; against pneumococci, Hib and other important (children's) diseases there are a vaccination protection). Still rare: tuberculosis.

    In adults: urinary tract infections, possibly also with inflammation of the renal pelvis, and pneumonia, for example due to flu viruses, pneumococci, rarely Q fever, tuberculosis, legionellosis.

    The rather rare Epstein-Barr virus infection (also called infectious mononucleosis or Pfeiffer's glandular fever) and toxoplasmosis lead to swollen lymph nodes (and more).

    Transmitted by tick bites: Lyme borreliosis, by scratching injuries in cats: the cat scratch disease (rarely it comes to severe courses with fever).

    Special infections acquired in pathogen endemic areas in Europe, the subtropics or the tropics, including rabies in Asia, for example. Also: the sexually transmitted disease gonorrhea (gonorrhea). Transmitted sexually and through contact with infected blood, for example through injuries or injections: for example hepatitis B, HIV infection.
  • Fever with impaired immune defense
  • Fever caused by a hospital germ, after blood transfusions or due to infections after procedures (for example abscess, necrotizing fasciitis; this is a severe infection with damage to the skin, subcutaneous tissue and fascia (connective tissue)).

Fever (initially often) of unclear cause *

  • Hereditary fevers (so-called autoinflammatory diseases)
  • Autoimmune diseases (collagenosis, rheumatism)
  • Inflammation of blood vessels (vasculitis diseases)
  • Drug fever
  • Tumors (cancer of various organs, the lymphatic system, blood)
  • Hormones & Co.
  • Mental ("habitual") fever

(* The links given here lead to the corresponding chapters in this article)

Measuring a fever in the ear: Most children tolerate this

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Diagnosis of fever

The detailed medical history, the course of the fever, a thorough physical examination, plus, depending on the suspected diagnosis, imaging examinations of internal organs, the ear, nose and throat area or the musculoskeletal and nervous system, plus blood tests: this is how the possible causes can be narrowed down.

Often special antibody tests help on the trail. It can also be possible to detect suspected pathogens under the microscope, to cultivate them from the blood (blood cultures, see chapter "") or to identify their genetic material. Sometimes a test for tuberculosis helps (for example, skin test, also tuberculin test).

Unfortunately, despite all efforts, there is sometimes no cause. If it remains unknown and the fever persists for more than three weeks with values ​​above 38 ° C, it is a fever of unclear origin.