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Fever: Causes, treatment, reduce fever

by Josephine Andrews
Published: Last Updated on 332 views

When you have a fever, your body temperature is higher than normal. With this heating up, the body defends itself against harmful influences such as invading pathogens. But malignant tumors and inflammatory autoimmune diseases also cause fever. Find out here when you have a fever, how exactly it develops, what causes it can have, and what you can do to prevent a fever.

quick overview

  • When do you have a fever? When the body temperature rises above 38 degrees Celsius.
  • Possible accompanying symptoms: dry and hot skin , shiny eyes, chills, loss of appetite, accelerated breathing rate, restlessness, confusion, hallucinations , etc.
  • Causes: very diverse, including infections ( flu , pneumonia, tuberculosis, Covid-19 , tonsillitis, measles , blood poisoning, etc.), accumulations of pus (abscesses), appendicitis , kidney pelvic inflammation, heart valve inflammation, rheumatic diseases, chronic inflammatory bowel diseases, stroke, tumors, etc .
  • When to the doctor? Adults: if you have a high, prolonged or recurring fever. Children: if the fever lasts longer than a day, is accompanied by other symptoms (drowsiness, rash, vomiting, etc.), antipyretic measures do not help, or a febrile convulsion occurs. Babies: at temperatures above 38 degrees Celsius.
  • Treatment: home remedies (drink a lot, calf wraps , lukewarm bath, etc.), antipyretic medication, treatment of the underlying disease

Fever: description

In principle, fever is not a threat: the increase in body core temperature is rather a declaration of war against harmful influences and threats. Certain defense mechanisms run faster in a warmer environment:

For example, when pathogens such as bacteria, parasites or viruses invade the body, the body activates its defense system. Various substances are released in the process, including so-called pyrogens . These are substances (such as cell debris, toxins, etc.) that give the brain the signal to heat up. Pyrogens that trigger fever can also be released during the work of the immune system against malignant tumors (cancer) and in autoimmune diseases.

Hyperthermia (overheating) should be distinguished from fever . The body temperature is also increased, but not by pyrogens. The best-known example of hyperthermia is heat stroke or sunstroke – a very warm environment leads to a dysregulation of the heat center in the brain. Antipyretics do not help against hyperthermia.

When do you have a fever?

The normal body temperature not only varies from person to person, but is also subject to its own daily rhythm. It is lowest at around 2 a.m. at night, but then slowly increases before waking up, only to reach its peak in the afternoon. Fluctuations of more than one degree can occur. On average, the normal body temperature ranges between 36.0 and 37.4 degrees Celsius (measured rectally) . But here, too, slightly different values ​​are given, depending on the accuracy of the measuring method.

In women, body temperature rises by about 0.5 degrees Celsius during ovulation and pregnancy.

If the body temperature rises above the normal level, physicians differentiate between the following gradations:

  • elevated temperature (subfebrile) : Temperatures between 37.5 and 38 degrees Celsius are referred to as subfebrile. Possible causes are infections caused by bacteria or viruses, but also heat stroke or intensive sport.
  • low-grade fever : 38 degrees Celsius is the limit mark of fever. A slight fever is present when the readings are between 38.1 and 38.5 degrees Celsius.
  • moderate fever : Temperatures between 38.6 and 39 degrees Celsius are considered a moderate fever.
  • high fever : If the readings are between 39.1 and 39.9 degrees Celsius, there is a high fever.
  • very high fever : This means a body temperature of more than 40 degrees Celsius.
  • extreme fever (hyperpyrexia) : Natural fever rarely reaches values ​​above 41 degrees Celsius. From 41.1 one speaks of hyperpyretic fever.

Very high and extreme fever can cause tissue and organ damage, making it dangerous. A body temperature above 42.6 degrees Celsius is usually fatal.

signs of fever

Fatigue , exhaustion, headaches , sensitivity to light and noise, a general feeling of illness – fever is often accompanied by various symptoms. The appetite also often decreases, the muscles and joints ache and you just want to have peace and quiet in bed. Depending on the severity of the fever, the following signs are also typical:

  • dry, hot skin
  • “feverish” shiny eyes
  • in children: whining
  • Feeling thirsty and profuse sweating
  • but during the rise in temperature shivering to the point of chills
  • sometimes indigestion with loss of appetite, diarrhea or vomiting
  • faster breathing
  • restlessness, confusion

Infants sometimes do not develop a fever even with severe infections. You should therefore pay attention to other possible signs of illness such as listlessness, noticeable sleepiness, refusal to drink, repeated vomiting, diarrhea, unusual skin color or skin rash. If you have these symptoms, you should see your pediatrician.

How does fever develop?

The body temperature is controlled in the brain: The heat regulation center is located in the so-called hypothalamus . It receives information about the ambient and organ temperature via cold and heat sensors in the skin and in the body.

If it gets too warm inside the body, the organism can take countermeasures by expanding the blood vessels in the skin and “ordering” increased sweating. If, on the other hand, the body gets too cold, the skin vessels constrict and goosebumps form, both of which help to curb the release of heat. At the same time, heat production is increased – through muscle tremors (“trembling from the cold”) and an increased metabolism.

Since the fever is also mediated by the same brain center, the typical symptoms can be explained: If the body is feverish (to fight pathogens, for example), the heat output is reduced. For this purpose, the skin vessels are narrowed, causing the skin to become pale and cold. The body sweats less, which supports the heating up inside. In addition, the metabolism is boosted and muscle tremors (shivers) are triggered – this increases heat production.

When the hypothalamus commands the fever to go down, the peripheral vessels dilate – the skin becomes warm and red. In addition, the patient begins to sweat. Excess heat is dissipated via both mechanisms and the body is thus cooled.

Fever: progressive forms

Physicians distinguish between different temperature profiles in fever:

  • Continuous fever : The temperature remains approximately the same for more than four days, reaching values ​​​​over 39 degrees Celsius and fluctuating by no more than one degree during the day. This course often occurs with bacterial infections such as scarlet fever , typhoid or bacterial pneumonia.
  • Remitting fever : The patient has fever practically all day, although less in the morning than in the evening (the difference is one to two degrees). A remitting fever is seen in some viral infections, tuberculosis, bronchitis, accumulations of pus and rheumatic fever.
  • Intermittent fever : Here the fever fluctuates even more significantly during the day. The body temperature is (approximately) normal in the morning and then rises to sometimes high fever values ​​in the evening (the difference is more than two degrees Celsius). This can be observed, for example, in pleurisy and pleurisy, blood poisoning (sepsis), salmonella infection (salmonellosis), inflammation of the inner heart wall ( endocarditis ) and bone marrow inflammation (osteomyelitis). Tumor diseases (such as Hodgkin’s disease ) can also trigger intermittent fever.
  • Undulating fever : A wavy (undulating) course of fever can occur, for example, with brucellosis . In the case of lymphomas (such as Hodgkin’s disease), the fever can also be undulating: fever phases lasting several days alternate with fever-free phases of about the same length. Doctors speak of Pel-Ebstein fever.
  • Recurrent fever : One speaks of a recurrent (or recurring) fever when there are regularly one or two (occasionally up to 14) fever-free days between individual fever attacks. Such a course is typical for malaria . Recurrent fever can also occur with certain bacterial infections. An example of this is five-day fever when infected with Bartonella bacteria.
  • Two-peak (biphasic) fever : After a few days of fever, the temperature returns to normal before a second phase of fever lasting several days follows. Such a two-peak fever curve can occur, for example, with measles or blood poisoning by meningococci (meningococcal sepsis).

How to measure fever?

The figures for average body temperature are all a little inaccurate. The reason is that body temperature is not only influenced by the time of day, activity and individual fluctuations, but also depends on the measurement method. The type and location of the measurement affect (slightly) the measurement result:

  • Fever measurement in the anus (rectal) : The measurement with the thermometer in the bottom is the most unpleasant, but also the most accurate method. The measurement result obtained comes closest to the temperature inside the body.
  • Temperature measurement under the tongue (sublingual) : Placing the clinical thermometer under the tongue also gives good results. These are usually around 0.3 degrees lower than in the rectal measurement. With the sublingual method, make sure that the lips are closed during the measurement (sometimes difficult with a blocked nose !). In addition, the patient must not have eaten or drunk anything cold or warm before the measurement, otherwise the result will be falsified.
  • Fever measurement in the ear (auricular) : The fever measurement using infrared waves in the ear is particularly useful for children because it is quick and easy. To do this, the probe must be inserted into the auditory canal, the easiest way is by gently pulling on the rear auricle . With otitis media and other ear diseases, it is better to take the temperature in the healthy ear.
  • Taking a fever under the armpit (axillary) : This is the most popular but the least accurate method of taking a fever. The measured temperature value can be up to 0.5 degrees below the actual temperature inside the body.

Fever: causes and possible diseases

The symptom fever associated with the flu or a bad cold is well known. In fact, infections with pathogens are the most common reason for an abnormally high body temperature. Sometimes, however, non-infection-related diseases such as appendicitis, rheumatism or cancer are behind it. So there are many possible causes of fever. Here are some common examples:

  • Cold (flu-like infection) and flu
  • Pneumonia (e.g. caused by pathogens such as pneumococci)
  • Covid-19
  • Infections with streptococci such as purulent tonsillitis, blood poisoning (sepsis) or inflammation of the inner wall of the heart (endocarditis)
  • inflammation of the renal pelvis
  • purulent abscesses
  • appendicitis
  • tuberculosis
  • Inflammation of blood vessels (vasculitis)
  • Diseases of the connective tissue (collagenosis)
  • Lymph gland cancer (non-Hodgkin’s lymphoma, Hodgkin’s lymphoma = Hodgkin’s disease) and other tumors
  • rheumatic diseases ( Bechterew’s disease , rheumatoid arthritis, systemic lupus erythematosus , etc.)
  • chronic inflammatory bowel diseases (Crohn’s disease, ulcerative colitis )
  • Chronic or alcoholic liver inflammation (hepatitis)
  • Hormone imbalances (Addison’s crisis, inflammation of the parathyroid gland, etc.)
  • Blockage of a blood vessel by a blood clot (thrombosis)
  • allergies

fever of unknown origin (FUO)

Doctors speak of fever of unknown origin (FUO) when a patient’s body temperature has been above 38.3 degrees Celsius for more than three weeks and no explanation can be found using standard examinations.

In many patients, the cause of FUO is ultimately found. These are often previously undiscovered infections, tumor diseases, rheumatic diseases or autoimmune diseases . Medications can also trigger a fever of unknown origin: Some people, for example, are hypersensitive to certain active ingredients in water tablets (diuretics), painkillers, antibiotics, sleeping pills or tranquilizers. The fever can be an expression of this “hypersensitivity”.

A fever of unknown cause is often observed in HIV patients . The triggers are often pathogens that normally – i.e. in people with a healthy immune system – do not cause an infection.

Causes of fever in children

Children suffer from fever more often than adults. In most cases, even small infections are enough to raise the temperature. The reference value for when fever is present is defined in the same way as for adults. It is 38 degrees Celsius.

Middle ear infections (otitis media), gastrointestinal infections, bacterial respiratory infections with tonsillitis, cough , runny nose and sore throat are usually responsible for fever in children. The little fever patients often also suffer from a typical childhood illness such as scarlet fever, measles or three-day fever. In rare cases, a severe bacterial infection (e.g. pneumonia, meningitis) or a rheumatic disease is the reason for an abnormally high body temperature.

Fever: when do you need to see a doctor?

Fever rarely occurs alone, but is usually accompanied by other symptoms. Depending on the underlying disease, these can be headaches and body aches, fatigue, chills, digestive problems such as diarrhea and vomiting, tachycardia and/or clouding of consciousness.

When you go to the doctor, you should not only depend on the body temperature, but also on the general feeling of illness and the severity of the additional symptoms. A high fever that lasts longer than a day should definitely be treated by a doctor. The same applies if symptoms such as drowsiness, confusion or febrile seizures occur. Then contact a doctor immediately!

Fever in children – when to see the doctor?

A pediatrician should be consulted if:

  • the fever has lasted for more than a day
  • fever-reducing measures such as calf wraps or suppositories have no effect
  • additional signs of illness such as barking cough, skin rash, diarrhoea, vomiting or drowsiness
  • a febrile seizure occurs

Babies under the age of three months should consult their pediatrician at temperatures above 38 degrees Celsius. If the baby does not develop a fever but shows the following symptoms, it is also advisable to see a doctor:

  • The baby behaves differently than usual, is noticeably listless, tired, and reacts less.
  • Diarrhea, vomiting, or refusing two meals a day is also a reason to see a doctor.
  • A skin rash or a change in skin color also indicates an illness and should be clarified by a doctor.

emergency febrile seizure

An estimated four percent of all children experience at least one febrile seizure. Such an epilepsy-like seizure can occur with infections and fever. It generally occurs between the ages of six months and five years. Small children between the ages of 14 and 18 months are most frequently affected.

A febrile seizure can be triggered by a rapid increase in temperature to 39 degrees Celsius and more. Especially when they first appear, the signs are very frightening for many parents:

  • The child becomes unconscious for a short time, does not react and is no longer responsive.
  • Muscles throughout the body may become stiff or begin to twitch.
  • The eyes are rolled up or the child stares.
  • When you hold your breath, your lips turn blue.

Most febrile seizures last three minutes or less and do not cause brain damage. After the seizure , the affected children are usually dazed and tired at first.

Most cases are uncomplicated febrile seizures : This is a febrile seizure that lasts less than 15 minutes, occurs in the typical age group (6 months to 5 years), and affects the whole brain (generalized). Complicated febrile seizures are less common : This is when a febrile seizure lasts longer than 15 minutes, recurs within 24 hours, occurs at an atypical age (< 6 months or > 5 years), or only affects a limited area of ​​the brain (focal seizure). ).

Important: If a febrile seizure occurs for the first time or lasts longer than three minutes, you should call the pediatrician or emergency doctor!

Fever: investigations

Since fever is a symptom, the underlying disease must be found. The first steps of the doctor are:

  • Through the detailed questioning (anamnesis) of the patient or the parents (in the case of sick children), the doctor gets information about the possible causes of the fever. He asks, for example, how long the fever has existed, whether there are other symptoms, whether the patient has recently had contact with sick people or animals or was abroad.
  • blood test shows, among other things, whether there is currently an inflammation in the body (elevated inflammatory parameters such as CRP).
  • physical exam can provide more information. For example, the doctor can listen to the patient ‘s heart and lungs , measure blood pressure and pulse, feel the abdomen and the lymph nodes in the neck and take a look at the mouth, throat and ears.
  • Further examinations may be necessary if the previous findings are unclear or if the suspicion of a specific disease needs to be clarified. For example, the patient’s sputum, urine and/or stool can be examined in the laboratory, the chest X-ray ( X-ray thorax ), an ECG or a cardiac ultrasound can be done, the abdomen can be examined using ultrasound or special blood tests (e.g. for tuberculosis) can be carried out .

Fever: treatment

What to do if you have a fever Fever is an important and natural defense reaction of the body against harmful influences. Viruses and bacteria can no longer multiply well at high temperatures. Therefore, fever does not always have to be treated. The basic rule is: If you have a fever, you must stay in bed! Simple remedies can also reduce the fever.

When to reduce fever

When you should lower a fever depends, among other things, on the cause, your physical condition, any existing previous illnesses and your personal level of suffering. If a child is severely affected and suffering from the fever, you should give the child a fever remedy from 38.5 degrees Celsius, but at the latest from 39 degrees.

Rules of conduct in the event of a febrile seizure

If a child has a febrile seizure, parents should heed the following tips:

  • Look at the clock and measure how long the seizure lasts.
  • Protect your child from injuries: lay them down so that they cannot fall down – for example in the cot or on the floor.
  • If the child vomits, you should turn them to the side so that the vomit can drain and is not swallowed.
  • Loosen the child’s clothing.
  • Don’t put a biting stick or similar in the child’s mouth in an effort to avoid biting the tongue – this often causes tooth damage worse than biting the tongue or cheek.
  • Don’t try to stop the twitching.

There is no reliable way to prevent febrile seizures. If your child is prone to febrile seizures, the most important thing to do is to prevent high temperatures. If the fever rises above 38.5 degrees Celsius, you should use home remedies for fever such as calf wraps or fever suppositories. You should definitely discuss the dosage of fever suppositories (or fever juice) with your pediatrician!

home remedies for fever

What to do if you have a fever In many cases, an elevated body temperature can be treated with simple antipyretic home remedies. These home remedies for fever have proven themselves over the decades:

Calf wraps for fever

Calf wraps are a tried and tested home remedy for fever. They dissipate excess heat from the body. Patients usually find the wraps very comfortable.

To do this, moisten a thin linen or cotton cloth with cool water. For adults, the temperature may be between 16 and 20 degrees Celsius. For calf wraps in babies, the water should be slightly warmer (about 28 to 32 degrees Celsius). Wrap the towels tightly around the calves of the outstretched legs and fix with one or two layers of dry towels. The feet and the rest of the body should be kept warm.

After five minutes, the calf wraps are removed again. But you can renew it two or three times. It is important to ensure that the fever is not reduced too quickly with the calf wraps – that would put too much strain on the circulatory system. Also, don’t do leg wraps if you’re shivering!

You can find out more about the application in the article calf wrap .

Curd wraps for fever

Cold or body-warm quark pads or wraps also help with fever. To do this, spread 250 to 500 grams of cool or slightly warmed quark as thick as a finger on a compress and fold the fabric once. There should be a protective layer of fabric between the curd and the skin. Place around the calves and fix with gauze bandages or towels. Leave on for 20 to 40 minutes.

You can find out more about this home remedy in the article Quark wraps (curd wraps) .

Abdominal and pulse wraps for fever

Another antipyretic home remedy is the pulse wrap . To do this, dip cotton towels in cold water, wring them out and wrap them around your wrists and ankles. The wrap is particularly suitable for babies with a fever. A belly wrap also helps babies with fever

You can read more about this in the article wraps, pads and envelopes .

Bathing with fever

You can also lower the fever with a cooling bath: The bathtub is first filled with warm water (the temperature should be about one degree Celsius below body temperature). Then you gradually add cold water at the foot of the tub until the bath water has dropped two to three degrees. Finish the bath after ten minutes. Afterwards, the patient should dry himself well and lie in bed.

Stop the bath immediately if the patient begins to feel chilly or cold.

heat bath can also help to overcome a feverish infection. It promotes sweating and boosts metabolism. This cold bath is helpful for mild fever. The bath water is heated exactly to the patient’s body temperature. Gradually let warm water run in at the foot end of the tub until the temperature has risen to 39 to 40 degrees Celsius. Bathe for 20 minutes and then dry well and rest well covered. Drink a lot.

If circulation problems occur during the bath or if the temperature becomes uncomfortable, stop the bath immediately. The overheating bath is not suitable for some heart diseases, neurological diseases and for small children.

You can read more about baths in the article Hydrotherapy .

Home remedies have their limits. If the symptoms persist over a longer period of time, do not get better or even get worse, you should always consult a doctor.

Drinks for fever

Do you drink much! Fever patients should ensure adequate fluid intake . The rule for this is: From a body temperature of 37 degrees Celsius, an additional 0.5 to 1 liter of liquid is required for every increase of one degree (in addition to the normal drinking amount of 1.5 to 2.5 liters per day).

Water and unsweetened tea are suitable drinks. Linden blossom and elder blossom tea are particularly recommended – they have a sweat-inducing and fever-reducing effect. Meadowsweet tea can also reduce fever.

Medicines for fever

If the fever is high and the patient is weak, fever-reducing medication in the form of tablets, infusions, medicinal juices or suppositories can be useful. Active ingredients include paracetamol , ibuprofen and acetylsalicylic acid. Discuss the use and dosage of such drugs with a pharmacist or doctor in advance.

Never give children with fever the popular painkiller and fever reliever acetylsalicylic acid (ASA)! In connection with viral infections, it can trigger the life-threatening Reye syndrome.

The most effective way to reduce fever is to treat the underlying condition. If, for example, a bacterial infection is behind the abnormally high body temperature, the doctor can prescribe antibiotics.

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