High temperature

High temperature (fever): Protective response of the body

High temperature, or fever, is a universal response of the body to infection or inflammation. It is one of the oldest protective mechanisms, indicating that the immune system is actively fighting pathogens. It is important to understand that fever is not a disease but a symptom and, in most cases, a useful ally in the fight against infection. An increase in body temperature creates unfavorable conditions for the replication of many viruses and bacteria and simultaneously activates the production of immune cells.

What is fever and how is it regulated?

The temperature of our body is regulated by a special center in the brain — the hypothalamus, which works like a thermostat. When infectious agents enter the body, immune cells produce special substances — pyrogens. These pyrogens act on the hypothalamus, forcing it to "reset" the thermostat to a higher level. The body begins to consider a new normal, for example, 38.5 °C, and activates mechanisms to reach this temperature: chills appear (muscle tremors to generate heat), and skin blood vessels constrict to reduce heat loss.

What should be considered a high temperature?

Common temperature reference ranges (measured rectally):

• Normal: up to 37.5 °C
• Subfebrile: 37.5 °C – 38.0 °C
• Feverish (moderate): 38.1 °C – 39.0 °C
• High (pyretic): 39.1 °C and above

However, the absolute number is less important than the overall condition of the person. This is especially true for children, as described in detail in the article "High temperature in children".

Why is a very high temperature dangerous?

Although fever is a protective mechanism, excessively high temperature (usually above 40–41 °C) places significant strain on the cardiovascular system and increases the risk of dehydration. In young children, a rapid rise in temperature can trigger febrile seizures.