Body temperature too high
An elevated body temperature is defined as a value of 37.5 °C to 38.4 °C or higher. From approx. 38.5 °C, we speak of fever. An increase in core body temperature can be caused by various factors (see “What influences body temperature?“). A body temperature of over 42.6 °C is fatal, as organ and tissue damage occurs above this value.
Hyperthermia occurs when the body’s core temperature rises above 37.5 °C. This is called hyperthermia. In this case, there is no setpoint increase in the core body temperature, i.e. the body’s own thermoregulation is counteracted (in contrast to fever).
The causes can be
- genetic defects (malignant hyperthermia),
- short-term heat development due to fluid deficiency in newborns (transitory hyperthermia),
- disorders of the thermoregulatory center (central hyperthermia),
- a lack of heat release (heat stroke) or
- an artificial hyperthermia in the context of a cancer treatment.
As a rule, hyperthermia occurs during high physical performance in a hot environment, whereas it is rather rare in the case of only external heat stress without physical work.
Hyperthermia manifests itself, in addition to an increased body temperature, through symptoms such as a reddened, overheated, initially usually dry skin, an increased respiratory rate, heart palpitations (tachycardia) and sometimes through changes in consciousness. Rarely, seizures or febrile convulsions occur as sequelae.
In heat stroke, overheating of the body takes place, while sufficient heat dissipation is no longer possible. The overheating can therefore not be sufficiently compensated by sweating alone. As a result, the function of the cardiovascular system is disturbed. Severe consequential damage can include life-threatening cerebral edema and multiple organ failure.
If the core body temperature exceeds approx. 38.5 °C, this is referred to as fever (pyrexia). Here, an increase in body temperature takes place as a result of a setpoint adjustment of the thermoregulation center, i.e. the body “intends” to increase the core body temperature. Heat production is increased and at the same time heat release is kept constant or reduced.
In many cases, fever takes place due to an immune response of the body (for example, to defend against flu viruses). Thus, the activity of many immune cells is increased when the temperature is elevated. At the same time, the growth of some pathogens is inhibited. However, if the fever rises above 41 °C, the body’s own proteins may be destroyed (denaturation) and blood clotting may be disturbed.
The point at which one can speak of a fever depends, among other things, on the measurement location and time of measurement. In a healthy adult, the mean normal temperature measured orally is between 36.4 and 37.7 °C. The temperature is lowest in the morning (maximum 37.2 °C) and higher in the afternoon to evening (maximum 37.7 °C). Derived from these values, a temperature measured orally in the morning or afternoon of over 37.2 °C or over 37.7 °C, respectively, can be considered a fever.
Fever temperature chart – Depending on the temperature, different levels of fever are distinguished:
|36,5 °C – 37,4 °C||Normal temperature|
|37,5 °C – 38,0 °C||Subfebrile Temperature|
|38,1 °C – 38,5 °C||Mild fever|
|38,6 °C – 39,0 °C||Moderate fever|
|39,1 °C – 39,9 °C||High fever|
|40,0 °C – 42,0 °C||Very high fever|
Fever reference values, depending on the measurement location:
|Anus (rectal)||Over 38,1 °C|
|Mouth (ora, sublingual)||Over 37,6 °C|
|Axilla (axillary)||Over 37,6 °C|
|Ear (auricular)||Over 37,6 °C|
A distinction is made between different types of fever:
- Infectious fever
- Resorptive fever
- Central fever
- Thirst fever
- Toxic fever
- Three-day fever
- Fever of unknown cause
The course of fever is usually characterized by:
- Rise in fever
- Fever height
- Drop in fever
An attenuated fever response may occur in neonates and the elderly. The fever response may also be weaker in patients who have chronic liver or kidney failure or who are taking glucocorticoids or other antipyretic medications.