Fever in adults – infections – msd manual edition for patients

Fever in adults - infections - msd manual edition for patients

Fever in adults

, MD, PhD, Warren Alpert Medical School of Brown University

Fever is an increased body temperature. A temperature is considered elevated if it is measured higher than 37.8 ° C orally or higher than 38.2 ° C rectally. Many people take the term "fever" very broadly and often mean that they feel too warm, too cold or sweaty, but they have not actually measured their temperature.

Although 37 ° C is considered a normal temperature, body temperature varies throughout the day. It is lowest in the morning and highest in the late afternoon, after which it can rise to 37.7 ° C. Even a fever never stays at a constant temperature. Sometimes the temperature peaks every day and then returns to normal – a process called intermittent fever. On the other hand, the temperature can fluctuate, but not fall back to normal – a process called remitting fever. Doctors no longer believe that the pattern of rising and falling fever is very important for the diagnosis of certain diseases.

Consequences of fever

The symptoms that people have are mainly triggered by the underlying disease and not by the fever itself.

Although many people are concerned that fever could harm them, a typical increase in body temperature to 38 ° C to 40 ° C, which is mostly caused by a short-lived (acute) illness, is well tolerated by most healthy adults. However, a moderate fever can be somewhat dangerous for adults with heart or lung disease because fever causes an increase in heart and respiratory rate. Fever can also worsen the mental state of people with dementia.

An extreme increase in temperature (typically above 41 ° C) can be harmful. Such a high body temperature can cause malfunction and ultimately failure of most organs. Such an extreme increase can sometimes be the result of very serious infections (such as sepsis, malaria or meningitis), but is typically more likely to be caused by heat stroke or certain medicines or drugs. Drugs that can cause extremely high body temperatures include cocaine, amphetamine, and phencyclidine, and drugs anesthetics and antipsychotic drugs.


Substances that cause fever are called pyrogens. Pyrogens can arise inside the body or come from outside. Microorganisms and the substances they produce (like toxins) are examples of pyrogens that are formed outside the body. Pyrogens that form inside the body are usually produced by monocytes and macrophages (two forms of white blood cells). External pyrogens can cause fever by stimulating the body to release its own pyrogens, or by directly affecting the area of ​​the brain that regulates temperature.

Infection is not the only cause of fever. Fever can also be the result of inflammation, a reaction to medication, an allergic reaction, an autoimmune disease (when the body produces antibodies that attack its own tissues) and undetected cancer (especially from leukemia and lymphoma).

Many disorders can cause a fever. They are roughly divided into:

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