Why don't we eat when we have a fever?

Self-help with a fever

fever(Pyrexia) got a bad rap. This is understandable: a fever indicates a physical state of emergency and is not exactly pleasant. Regardless of this, fever also has positive effects: It can be assumed that fever stimulates the body's defenses and supports self-healing powers.

Variable body temperature

While the Skin temperature of man z. B. can be very different depending on the ambient temperature, is the Core body temperature fairly constant in the region of about 37 ° C. This is ensured by the temperature center in the brain, which, comparable to the thermostat of a heating system, specifies the “target temperature”.

However, certain fluctuations are normal. The body temperature is lowest in the morning and reaches its maximum in the late afternoon. In adults, normal body temperature fluctuates by about one degree during the day. Everyone has a slightly different “operating temperature”: 36.0 ° C in the morning are therefore just as normal, depending on the “type”, as 38.0 ° C in the late afternoon (these temperatures reflect the value measured in the anus, i.e. rectally , temperatures in the mouth are around 0.5 ° C lower). The daily rhythm is only less pronounced in small children - the normal body temperature here only fluctuates by around 0.5 ° C.

In women, there are additional temperature fluctuations: In the second half of the cycle (after ovulation), the body temperature increases by around 0.3 ° C. The regular measurement of the temperature can be used for contraception (basal temperature method).

Many people assume a rigid normal body temperature of mostly 37 ° C and diagnose themselves as having "under-temperature" if they measure less. Such a “sub-temperature” is harmless. The fluctuations in the course of the day are also very individual and also depend on the measurement location. Here's how medical textbooks state as normal:

  • Axillary (armpit): 34.7 ° C-37.5 ° C
  • Oral (mouth): 35.5 ° C-37.5 ° C
  • Rectal (anus): 36.6 ° C-38.0 ° C
  • Auricular (in the ear, i.e. on the eardrum): 35.8 ° C-38.0 ° C

When does a fever start? Usually an increase in the rectally measured body temperature to 38.5 ° C or more is called a fever. In the gray area between 38.0 ° C and 38.5 ° C, some doctors also speak of increased or subfebrile temperature. In infants and toddlers, the "fever limit" is lower; temperatures above 38 ° C are to be regarded as a fever.

What causes a fever?

Fever is triggered by messenger substances in the immune system, which are always released when the body is struggling with inflammation. Such inflammations are usually caused by infectious agents (viruses, bacteria, fungi, parasites), but sometimes also by autoimmune processes or other defense processes, for example in the case of cancer or after operations. Fever also rarely develops in allergic reactions, as a side effect of medication or in the case of an overactive thyroid.

The temperature setpoint in the brain is raised by inflammation processes. The body is now trying to achieve the new “target” - cool skin, freezing and trembling to the point of chills are the well-known signs of this rise in fever.

This is to be distinguished from fever Overheating (Hyperthermia) due to excessive heat supply from outside: This can occur with heat exhaustion or sunstroke, or with some - very rare - diseases of the metabolism in the muscles. With the latter, also as malignant hyperthermia In the case of hereditary problems, the metabolism in the muscles derails after the administration of certain anesthetics. As a result, the muscles generate a lot of heat - the body temperature can then rise to over 44 ° C.

Consequences of the fever

As a result of the fever, the metabolism is increased. As a result, the body consumes more oxygen and converts more water. At the same time, the brain cells become more irritable. B. through more active dreams to daydreams and hallucinations, the so-called Fever delir. The increased irritability of the brain can lead to seizures in epileptics. Benign febrile seizures can occur in children under 5 years of age.

Even if we sometimes worry about "burning up" in a fever - in contrast to overheating, dangerous or even fatal overheating or permanent damage practically does not occur with an infection-related fever. The fever caused by inflammation practically never rises above 41.5 ° C - higher temperatures are only found in some very rare diseases (e.g. Reye's syndrome, severe brain inflammation and tetanus).

The higher the worse?

It is often assumed that the higher the fever, the more dangerous an illness is. This is true for some diseases: For example, a high fever in the case of a urinary tract infection often indicates that the renal pelvis or the kidney tissue are involved. On the other hand: some relatively harmless colds are accompanied by a high fever, while other, far more dangerous infections (e.g. some forms of meningitis) lead to a comparatively mild fever. Infections that take a very serious course, such as sepsis (blood poisoning), are sometimes even associated with normal or low temperatures.

Fever - Useful or Harmful?

It has been known for a long time that parts of the immune system work faster at elevated temperatures. So z. B. in fever produces more antibodies. The aggressiveness of some pathogens (the Virulence) at higher temperatures.

The following experiment also suggests a possible benefit of the fever: When lizards are artificially infected (for example by injecting pathogens into their bodies), they instinctively seek out sunny places - the cold-blooded animals increase their body temperature by several degrees as a result. If one prevents some of the animals from leaving the shade, they show a higher mortality than those that could move to sunny places. At least in the case of reptiles, “fever” clearly has a disease-fighting function.

In addition, experiments with the flu (influenza) show: the duration of the illness is on average three days shorter if an antipyretic treatment is dispensed with. It is not certain whether this also applies to other infectious diseases.

We assume that the body does not demand the additional work associated with the fever in vain and that fever generally supports the immune system. In most cases, it is not the fever that is threatening, but the illness that the body fights with a fever!

When to the doctor

The condition of the fever is more decisive than the level of the fever. The rules apply here:

  • Heavily pregnant, weakened or sick people should see a doctor at an early stage.
  • If it is unclear what is causing the fever or if symptoms are worrying (such as bleeding from the skin), you should see a doctor.
  • This also applies to recurring fever or if fever recurs after a fever-free period of a few days or even despite treatment.
  • A doctor should also be consulted in the event of fever-related complications - such as fever delirium or dehydration.
  • Infants under six months of age with a fever (i.e., body temperature greater than 38.0 ° C) should be evaluated by a pediatrician. Older infants should see a pediatrician at temperatures over 38.5 ° C and toddlers at over 39 ° C if no cause, such as a cold, can be determined.

What to do if you have a fever

Because we assume that fever supports the healing process, we do not recommend lowering the fever in every case. In many cases, simple measures can provide relief and help the body cope better with the increased temperature:

  • Rest breaks: whether only on the couch or as strict bed rest.
  • Clothing: Airy, breathable cotton clothing and a jacket that can be put on or taken off as required.
  • Food: Light food relieves the circulation, e.g. B. steamed vegetables or a light soup.
  • Fluid: For every degree of temperature increase, the body needs an additional liter of fluid per day. So: always grab a glass of water, tea or diluted fruit juices are also suitable. Often warm or hot drinks are preferred when the fever rises (one “feels cold”), otherwise cool (but not ice-cold) drinks are the right choice. You will drink enough if you urinate about as much as you would on healthy days.

Because older people in particular sleep a lot with a fever, the risk of dehydration is increased. Here you often have to remind yourself to drink or give something to drink at regular intervals when you are awake - the affection associated with this is also good for you.

When to lower the fever?

If the fever is too stressful for the body, lowering the fever is indicated. This applies if:

  • The feverish can no longer keep up with drinking and dehydration is to be feared.
  • The feverish patient has a delirium of fever, i.e. is hallucinated and disoriented.
  • The feverish person is already weakened, e.g. B. from a heart failure or a chronic lung disease such as emphysema.
  • You have epilepsy (it is best to ask your doctor here).
  • You “really suffer” or have pain, such as a headache. A fever medication (which is also a pain reliever) can then e.g. B. help to better sleep.
  • The feverish person does not want to or cannot report sick (e.g. on a business trip) or the family needs further care.

How to lower the fever?

It often helps to dress more easily or just cover up thinly.

Wet compresses such as leg compresses or washing can also dissipate heat, and the same applies to a lukewarm bath.

However, the effect of such "external cooling" differs from case to case and depends primarily on the fever stage Rise in fever low (what you notice in cold hands and cold feet) - cold compresses placed on the skin cannot “pick up” any heat, so they are almost ineffective. External applications only make sense if you “glow”. The wraps must not be too cold, otherwise the skin circulation is reduced from the outside (cold causes the blood vessels to constrict) - the body's heat cannot then be dissipated to the outside either.

Special text: Medicines to lower fever

Measures of naturopathy

Traditional phytotherapy names the herbal active ingredient with an antipyretic effect Willow bark (Bark of the white willow Salix) - the salicylates contained in it act like "natural aspirin": Heat a teaspoon of bark with ¼ liter of cold water very slowly to a boil, then let it steep for five minutes, strain and drink in sips.

A sweaty effect becomes Elderflower and Linden blossom attributed to. Those who believe in vitamin C are better advised to take natural sources such as tropical fruits, cherry juice, and beetroot juice, which are good for mixing with water, than vitamin supplements.

Highly dosed vitamin C is recommended again and again in the case of fever to increase the immune system, but a positive effect cannot be scientifically proven, at least in the case of colds.

Measure a fever

General information about fever

Do you “have to” measure the temperature with every cold? Not necessarily. For one thing, most of us can tell when we have a fever even without taking a measurement. Second, the height of the fever is not a good measure of how severe an illness is. Nevertheless, the measurement can sometimes help in assessing the course of the disease, for example

  • If the doctor recommends the measurement - e.g. B. to be able to better assess the "impact" of a therapy.
  • In children under three years of age. On the one hand, illnesses are often more difficult to detect here, on the other hand, febrile children without clear signs of illness should always be presented to the doctor.
  • Before going to the doctor or calling him for advice. It is often helpful for the doctor to know whether a certain clinical picture runs with a fever or without it.

How to measure

If you decide to check the temperature, "feeling" is only partially sufficient: As the fever rises, the blood vessels in the skin constrict and therefore let less heat penetrate the skin. When the fever drops, the opposite happens - you lie on your hands so often wrong.

Various thermometers are available today for more precise measurements. The most accurate measurement method is the rectal measurement, i.e. the measurement in the buttocks (Rectal temperature). This type of measurement best reflects the internal temperature of the body (core body temperature).

But also in the armpit (axillary measurement) or under the tongue (sublingual measurement) the temperature can be measured with sufficient reliability. However, you then have to add about half a degree to the measured temperature in order to obtain a value that is comparable to the rectal temperature. The easiest, but also the most expensive and unfortunately not always 100% reliable, is the measurement in the ear (auricular measurement).

Since the body temperature can rise by up to 1 ° C due to physical exertion, it is best to rest for half an hour before taking a fever. Clothing that is too warm can also increase the temperature - especially in small children - by up to 0.5 ° C.

This is how it works:

  • Rectal: Make the tip of the thermometer slippery with a little petroleum jelly, another skin cream or just a little tap water and carefully insert it so that at least the measuring cone is securely in the anus.
  • Under the tongue: Park the thermometer tip quietly under the tongue for several minutes with your mouth closed (preferably on the side under the edge of the tongue).
  • In the armpit: clamp the thermometer tip in the armpit from the front, hold still. The measurement under the armpit takes the longest of all measurement types - up to 10 minutes. Alternatively, you can measure in the bar.
  • In the ear: Put the measuring sleeve on the measuring head (does not apply to every model). Hold the measuring head gently in the ear canal - the measuring head should sit tightly without pressing or hurting (it is best to pull the auricle upwards at an angle). The measurement is started by pressing the measurement button.


Dr. med. Herbert Renz-Polster in: Gesundheit heute, edited by Dr. med. Arne Schäffler. Trias, Stuttgart, 3rd edition (2014). | last changed on at 10:14