Brief overview
- Description: Fever is when the body temperature rises above 38 degrees Celsius. Other indications include dry and hot skin, shiny eyes, chills, loss of appetite, accelerated breathing rate, confusion, hallucinations.
- Treatment: Home remedies (e.g., drinking plenty of fluids, calf compresses, lukewarm bath), antipyretic medication, treatment of the underlying disease.
- Diagnosis: Consultation with a doctor, measuring fever in the anus, under the tongue, in the ear, under the armpit, on the surface of the body with infrared, in intensive care also with the aid of catheters in the bladder or arteries, physical examination, if necessary blood examination and imaging procedures
- Causes:Infections (such as influenza, pneumonia, tuberculosis, covid-19, tonsillitis, measles, blood poisoning), pus accumulations (abscesses), inflammations (for example appendix, renal pelvis, heart valves), rheumatic diseases, chronic inflammatory bowel diseases, stroke, tumors.
- When to see a doctor? Adults: In case of high, prolonged or recurrent fever. Children: If the fever lasts longer than one day, is accompanied by other complaints (e.g. dizziness, rash, vomiting), fever-reducing measures do not help or a febrile convulsion occurs. Infants: If the temperature is above 38 degrees Celsius.
What is fever?
Body temperature is controlled in the brain: the heat regulation center, which sets a target value for body temperature, is located in the hypothalamus. Ambient and organ temperatures are determined via cold and heat sensors in the skin and in the body. In this way, the setpoint is compared with an “actual value” of the current body temperature.
If the “actual value” and the target value differ, an attempt is made to adjust the temperature to the target value.
If the body temperature is below the setpoint, we freeze. This causes goose bumps, muscle tremors and constriction of the blood vessels in the limbs. This leads to cold hands and feet, for example. This is the body’s attempt to raise the temperature inside the body.
If the “actual value” rises above the setpoint, excess heat is dissipated. This occurs primarily through sweating and increased blood flow to the skin on limbs or even the ears.
The body coordinates heat-producing or heat-maintaining processes, external temperature influences and “cooling” countermeasures in such a way that the setpoint is constantly maintained.
The body now favors heat-generating and heat-maintaining processes. One begins to freeze (shivering) and the temperature rises until the new set point is reached. This results – sometimes suddenly – in fever. When the set point drops back to normal – i.e. when the fever subsides – the patient sweats more to bring the temperature back down.
The increased temperature accelerates and promotes processes in the body that serve to defend against pathogens or other harmful influences in the body.
Basically, fever is therefore nothing threatening, but a natural reaction of the body, which serves the defense against harmful influences. Thus, fever is actually a good sign, as it means that the body is fighting back.
However, if the temperature rises too high (above 41 degrees Celsius), the high temperature may also harm the body.
Fever in itself is not contagious, as it is an individual reaction to a particular stimulus. However, if such a stimulus is a pathogen such as bacteria or viruses, these may very well be contagious and, in the event of infection, may also cause fever in other people.
When does one start to have a fever?
Under certain circumstances, the body temperature can fluctuate up to more than one degree. On average, the normal body temperature ranges between 36.0 and 37.4 degrees Celsius (measured rectally). But even here, depending on the accuracy of the measurement method, values are sometimes slightly different.
In accordance with this dynamic, fever is highest in the evening, if necessary, and may rise seemingly “while you sleep.” Then, in the middle of the night or in the morning, the temperature often drops again, even with fever. However, stronger fever in the evening is also one of the characteristics of some diseases such as tuberculosis or sepsis.
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 distinguish between the following gradations:
- Elevated temperature (subfebrile): Temperatures between 37.5 and 38 degrees Celsius are called subfebrile. Possible causes are infections caused by bacteria or viruses, but also heat stroke or intensive sports.
- Slight fever: From 38 degrees Celsius, the medical term is fever. A slight fever is present at readings between 38.1 and 38.5 degrees Celsius.
- Moderate fever: Temperatures between 38.6 and 39 degrees Celsius are considered a moderate fever.
- Very high fever: This refers to 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 fevers may cause tissue or organ damage and become dangerous. A body temperature above 42.6 degrees Celsius is usually fatal.
Fever phases
Medically, fever can be divided into different stages or phases:
- Fever increment (stage incrementi): An attempt is made to raise the temperature – with the help of goose bumps and shivering, among other things – by increasing the set point. For example, shivering or cold hands occur. Covering up and warm drinks are now pleasant. In children predisposed to this, febrile convulsions may occur during this phase.
- Fever height (fastigium): In rare extreme cases of high fever, febrile delirium occurs with clouding of consciousness and senses.
- Fever subsidence (defervescence, stage decrementi): The decrease in fever occurs slowly (over the course of days) or rapidly (over the course of hours). Sweating with loss of fluids is common – hands, head and feet may also feel warm. If the drop is very rapid, there are occasional circulatory problems.
Progressions
- Continuous fever: temperature remains about equally elevated for more than four days, reaching values above 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 fever, or bacterial pneumonia.
- Remittent fever: the patient has a fever practically all day, but less in the morning than in the evening (the difference is one to two degrees). A remittent fever is seen, for example, in some viral infections, tuberculosis, bronchitis, pus accumulation, and rheumatic fever.
- Intermittent fever: In this case, the fever fluctuates even more markedly during the course of the day. Body temperature is normal in the morning and then rises to sometimes high fever levels by evening. This pattern can be observed, for example, in blood poisoning (sepsis), but also under certain circumstances in tumor diseases (such as Hodgkin’s disease).
- Undulating fever: A wave-like (undulating) course of fever occurs, for example, in brucellosis. In lymphomas (such as Hodgkin’s disease), the fever may also be undulating, with fever phases lasting several days alternating with fever-free phases of approximately the same length. Physicians refer to this as Pel-Ebstein fever.
- Two-peaked (biphasic) fever: After a few days of fever, the temperature drops back to normal values before a second fever phase lasting several days follows. Such a two-peaked fever curve occurs now and then, for example in measles or blood poisoning caused by meningococci (meningococcal sepsis).
In former times these courses were of high importance. Nowadays, they are rarely observed in this typical form, since fever is usually controlled at an early stage by appropriate measures.
How long fever lasts depends strongly on the underlying disease and the respective reaction of the affected person. The time span ranges from a few hours to several days or even a few weeks.
Hyperthermia
To be distinguished from fever is overheating (hyperthermia). In this case, the body temperature does not rise due to pyrogens and their temperature set point increase. Rather, the set point remains unchanged, but can no longer be maintained by heat dissipating measures of the body.
This happens, for example, during physical activity or due to exhaustion, especially in high heat or humidity, or when clothing is worn that restricts cooling by sweating. Also, if too little is drunk, the risk of hyperthermia increases.
Instead, it is advisable to move affected persons to a shady place, remove excess clothing if necessary, and slowly lower the temperature with cool compresses and drinks. The use of ice or ice-cold drinks is not advisable, as rapid, extreme temperature differences put a great strain on the circulation.
How can fever be reduced?
What helps with fever? Fever is an important and natural defense reaction of the body against harmful influences. Viruses and bacteria multiply more poorly at high temperatures. Therefore, fever is not treated in every case.
As a general rule, it is essential to stay in bed when you have a fever! Do not go to work with a fever (above 38 degrees Celsius). Apart from the fact that productivity also suffers with a higher fever, there is also the risk of infecting colleagues with a possibly contagious disease.
At what point it makes sense to reduce a fever depends, among other things, on the cause, the physical condition, any pre-existing illnesses and the personal level of suffering. For example, if a child is severely affected by the fever and is suffering, that is reason enough to try to reduce the fever as early as between 38.5 and 39 degrees Celsius.
Home remedies against fever
Calf wrap
Calf wraps are a time-honored measure against fever. They remove excess heat from the body. Patients usually find the compresses very pleasant.
To do this, moisten thin linen or cotton cloths with cool water. For adults, the temperature may be between 16 and 20 degrees Celsius, for calf wraps on babies slightly above (about 28 to 32 degrees Celsius).
Wrap the cloths tightly around the calves of the outstretched legs and fix them with one or two layers of dry cloths. The feet and the rest of the body are ideally kept warm.
After five minutes, remove the calf wraps. However, they can be renewed two or three times. Be careful not to reduce the fever too quickly with the calf wraps, as this may put unnecessary strain on the circulation. Also, avoid calf wraps if you have chills!
You can learn more about the application in the article Calf compresses.
Quark compress
Cold or body-warm quark compresses 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. Ideally, you should also place a protective layer of fabric between the quark and the skin.
Place the curd compress around the calves and fix it with gauze bandages or towels. Leave to take effect for 20 to 40 minutes.
Belly and pulse compress
Another fever-reducing home remedy is the pulse wrap. To do this, soak cotton cloths in cold water, wring them out and wrap them around the wrists and ankles. The wrap is especially good for feverish babies. A belly wrap also helps these sensitive patients.
Always make sure with babies that their body temperature does not drop too quickly or too far.
Read more about this in the article Wraps, compresses and poultices.
Bathing with fever
A fever can also be reduced with a cooling bath: To do this, first fill the bathtub with warm water (the temperature is at best about one degree Celsius below body temperature). Then gradually add cold water at the foot of the tub until the temperature of the bath water has dropped by two to three degrees.
After ten minutes, stop the bath. Dry off well afterwards and put to bed.
Stop the bath immediately if the patient begins to shiver or freeze.
A hyperthermic bath may also help to lower the temperature during a febrile infection. It promotes sweating and boosts metabolism. This cold bath is helpful for mild fevers.
If circulation problems occur during the bath or the temperature becomes uncomfortable, stop the bath immediately. The overheating bath is not suitable for some heart diseases, neurological conditions and for young children.
Similar effects can be achieved in the shower, but the temperature differences between the head and extremities are more difficult to adjust. In addition, any circulatory problems that may occur when taking a cold shower while standing may have more serious effects (for example, dizziness and falls). Therefore, a bath is usually the better alternative.
In any case, be careful not to cause extreme, sudden temperature differences and choose a temperature in which they feel comfortable.
Read more about baths in the article Hydrotherapy.
Homeopathy
There are numerous homeopathic remedies that – depending on the cause – are supposed to help against different forms of fever, for example “Aconitum” or “Belladonna”.
However, the concept of homeopathy and its specific efficacy are controversial in science and not clearly proven by studies. If you have questions about this, it is best to contact a doctor who also offers complementary healing methods.
Drinks for fever
In the case of fever, it is important to ensure sufficient fluid intake. The rule for this is: from a body temperature of 37 degrees Celsius, an additional 0.5 to 1 liter of fluid is needed for every increase of one degree (in addition to the normal drinking amount of 1.5 to 2.5 liters per day).
During the rise in fever, one usually feels more like warm drinks (chills). Later, drinks at room temperature are good, for example water or unsweetened tea. Lime blossom and elderflower teas are particularly recommended – they have a diaphoretic and fever-reducing effect. A tea made from meadowsweet may also reduce fever.
Medication against fever
If the fever is high and the patient is weak, antipyretic drugs in the form of tablets, infusions, medicinal juices or suppositories may be useful. Effective ingredients include paracetamol, ibuprofen and acetylsalicylic acid. Discuss the use and dosage of such medications with a pharmacist or doctor in advance.
Never give children with fever the popular painkiller and antipyretic acetylsalicylic acid (ASA)! In connection with viral infections, it sometimes triggers the life-threatening Reye syndrome.
Fever: examinations and diagnosis
Since fever is merely a symptom, the underlying illness must be found.
Detailed questioning (anamnesis) of the patient or the parents (in the case of sick children) gives the doctor clues to the possible causes of the fever. For example, it is important to know how long the fever has been present, whether there are any other complaints, whether there has been recent contact with sick people or animals, or whether you have been abroad.
A physical examination often provides more information. For example, the doctor listens to the patient’s heart and lungs, measures blood pressure and pulse, palpates the abdominal and cervical lymph nodes or takes a look at the mouth, throat and ears.
Sometimes further examinations are necessary if the previous findings are unclear or if there is a suspicion of a particular disease. For example, laboratory tests of blood, urine or stool, examinations with imaging techniques (for example, X-ray, ultrasound) or special blood tests (for tuberculosis, for example).