Fever means that the body temperature of a person rises above the normal level. Fever is not a disease in itself, but a symptom of the body’s struggle with something. It is often caused by intruders such as bacteria, viruses and other pathogens, but also by foreign substances that the body fends off. In addition, the fever can also be caused by serious diseases. Fever is also called pyrexia in medical terminology.

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Fever occurs when the body sets the temperature to higher than normal. Pathogens are involved, but also tissue hormones – the prostaglandins. The body forms these to control viruses and bacteria. This is because many defence reactions are accelerated when the temperature is raised. Conversely, fever makes life difficult for germs of all kinds.

Fever is therefore usually a sensible reaction of the body, which you should not suppress hastily. Nevertheless, there are situations in which it is better to lower the fever, for example, when the circulation is weak and unstable.

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At what time is it fever?

The center for heat regulation in the brain works similar to a thermostat. It controls the body temperature around the clock. Some factors can raise the “set point”. Then the body adjusts the temperature: It increases. But not every increase in body temperature immediately means fever.

The following values apply to body temperature (for measurements in the Po/After = rectal):

  • The normal temperature inside the body (body core temperature) is normally between 36°C and 37°C for adults (children: 36.5 to 37.5°C). However, this value varies from person to person and depends, for example, on physical activity. In addition, the body temperature fluctuates throughout the day: it is lowest in the morning and highest in the evening.
  • You have a higher temperature if the values are between 37°C and 38°C (subfebrile temperature). In children this value is between 37.6 and 38.4°C.
  • Doctors speak of fever in adults when the core body temperature climbs higher than 38°C (children: from 38.5°C).
  • High fever is present when the temperature exceeds 39°C to 41°C (children: from 39.5°C and adults: from 39°C). Especially for small children, temperatures of 38 to 39°C are not uncommon.
  • A person has an extremely high fever (hyperpyrexia) if the temperature exceeds 41°C.
  • Above values of 42.5°C fever can be fatal.

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Signs of fever in adults

There are several signs that occur together with fever. In adults, for example:

  • paleness, pale skin
  • Fatigue, exhaustion, reduced performance
  • glazed eyes
  • Limb Pain
  • Chills
  • Loss of appetite and lack of desire to consume drinks

Fever in children and babies

Babies and small children have fever much more frequently than adults because their immune system is not yet sufficiently trained. It comes into contact with many pathogens or irritants for the first time. The immune system usually reacts to these faster and more violently. Thus, fever often rises faster and higher in children than in adults. In addition, the temperature regulation in small children does not yet function perfectly. They sweat less and therefore develop fever more quickly.

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Babies and younger children generally have a higher body temperature than older children, for example because their metabolism is more active. It should be noted that a baby’s immune reactions can be so weak that it will not develop a fever even in the event of a serious infection.

Babies and children often show the following symptoms of fever:

  • burning, reddened face (red cheeks)
  • tired eyes
  • cool, pale, bluish skin on the body
  • It seems limp, apathetic and very sick
  • It nags, whines and cries often
  • It has no appetite and does not want to drink
  • When the fever drops again: It sweats and feels a great thirst for cold drinks.

If you discover such signs in your child, always take the temperature first and see your pediatrician with him/her soon.

Body temperature is never the same

The body temperature of a human being is not constant, but changes due to various factors. Some examples:

  • Age: Seniors often have a lower body temperature than young people.
  • Time of day: In the morning, the body temperature is lower, during the day it increases by about 1°C.
  • Sport can increase the temperature by up to 2°C.
  • Lush and spicy meals can heat up the body.
  • Ovulation: Body temperature rises by about 0.5°C in the middle of the menstrual cycle and remains elevated until menstruation begins. Some women use this fact to determine their fertile days. However, as the only method of contraception, the temperature method is risky.
  • Type of fever measurement: Determining the body temperature in the mouth (oral), under the armpit (axillary), in the anus/po (rectal) or ear (auricular) provides different values. When measuring in the ear and mouth, the temperatures are always somewhat lower. A measurement under the armpit is considered very inaccurate and is therefore not recommended.

Fever: Possible causes

Fever is a protective reaction of the body to certain influences. The increased body temperature shows that the immune system is active and running at full speed. It tries to fend off invading germs or foreign substances. There are many possible reasons for fever.
An infection is often the cause

A very common cause of fever is an infection with bacteria, viruses, fungi and other parasites. Well known are the common cold (flu caused by cold viruses) and the flu (influenza caused by influenza viruses). But many childhood illnesses are also accompanied by fever. The organism tries to make it as uncomfortable as possible for the intruders. This is because pathogens feel less comfortable at high temperatures and are less able to multiply. Fever is therefore a completely normal and – to a certain extent – healthy defensive reaction of the organism.

  • Other causes of fever

In addition to infections, there are other possible causes of fever. Some examples:

  • vaccinations: After a vaccination, a slight fever is a relatively common reaction of the immune system. Children in particular often have an increased body temperature after a vaccination.
  • Teething in children: This process demands a lot of energy from children and they sometimes get a fever.
  • Medication: some antibiotics, cytostatics (chemotherapy for cancer)
  • Drugs, for example Ecstasy
  • Many diseases are associated with an elevated body temperature or fever. Examples: rheumatological diseases (rheumatoid arthritis, fibromyalgia, ankylosing spondylitis), tumors (gastrointestinal, kidney, immune system), chronic inflammatory bowel diseases (Crohn’s disease, ulcerative colitis) or diseases of the connective tissue and blood vessels. Allergies can also cause fever.
  • Heat as the cause of fever in summer: anyone who spends too long in the sun without protection risks sunstroke or life-threatening heat stroke. This causes the body to overheat and fever can develop. You must act immediately and consult a doctor! The body temperature also increases if you are not used to heat and are dressed too warm or have drunk too little. In addition, the so-called “summer flu” also occurs during the hot season. Insect bites or contact with jellyfish can also cause fever in summer.
  • Fever after an operation is always an alarm signal indicating an infection – pathogens have then entered the body through wounds. After an operation, you have an easier time of it because the immune system of freshly operated patients is weakened. Doctors must then act immediately!
  • Stress can also be the cause of fever, because the psyche also influences body reactions. When under stress (fear, excitement, joy), the organism releases more messenger substances that put it on alert. If this state lasts longer, it can react with fever.
  • Fever after a tick bite always means: Off to the doctor! Ticks can transmit dangerous pathogens: Borrelia (bacteria that cause Lyme disease) and the TBE virus. It causes a dangerous meningitis, the early summer meningo-encephalitis (FSME). Usually flu-like symptoms are added.

Fever: accompanying symptoms are important for diagnosis

Depending on the cause of the fever, there are various accompanying symptoms that provide doctors with clues to the trigger. The fever is not always constant in most people, but changes during the course of the day and as the disease progresses or heals. An example: when the fever rises, the affected person is often cold and has chills. When the fever falls, patients usually sweat profusely and their cheeks seem to glow.

Some examples:

  • Cold: A harmless cold often announces itself with headaches, aching limbs, a cold, coughing and a slight fever. Then you have caught cold viruses. Even without treatment, the cold will subside within a few days.
  • Influenza: Influenza causes similar symptoms to a cold, but these start suddenly and are more severe.
  • Meningitis: It is accompanied by severe headaches, stiff neck, fever and aching limbs.
  • Tuberculosis and pneumonia: Cough and fever can also indicate these infectious diseases of the respiratory tract. In children, pseudocrupp is also a possible cause of life-threatening respiratory distress and manifests itself in severe coughing attacks (croup cough).
  • Gastroenteritis: Fever, diarrhea and/or vomiting are typical symptoms of gastroenteritis. Poisoning (food, fungi, plants, chemicals) can also trigger fever and vomiting.
  • Childhood illnesses such as measles, chickenpox, rubella or scarlet fever: Then, in addition to the fever, a rash appears on the skin, which is usually characteristic of the respective infectious disease. Three-day fever and hand-foot-and-mouth disease in children also cause fever and rash.

Sometimes fever without accompanying symptoms also occurs. Doctors regard this as a sign that the immune system is working successfully. It was obviously able to fight off the pathogen before it could cause further symptoms. However, the fever should then drop again after a short time.

If the fever persists for a long time or recurs repeatedly without any apparent reason, you should always consult a doctor and have the cause clarified.

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