When is a fever dangerous in adults?

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A fever is a sign that your body is trying to overcome an illness or underlying infection. Viruses and bacterial infections are notorious for causing fevers, but there are other medical problems such as autoimmune disorders and severe dehydration that can trigger a fever.

In a healthy adult, a normal, oral temperature reading should be above 36.1 degrees C, but below 37.2 degrees C. One degree above 37.2 degrees C is considered a fever in an adult.

Temperature Spike

Some illnesses produce a low-grade fever of about 38.3 degrees C on an oral thermometer, which can easily be treated with hydrating liquids and plenty of rest and relaxation. A fever of 38.9 degrees C may require the addition of an over-the-counter fever reducer such as acetaminophen to assist the body in bringing the fever down. But, when an adult's temperature begins to spike at 39.4 degrees C and above, Banner Health reports, that there may be a cause for concern.

Duration of Fever Danger

A spiking fever can be dangerous and often requires medical intervention, especially if the high fever lasts for more than 72 hours. According to the Medical University of South Carolina (MUSC), when a high fever persists, it can be dangerous. It can also be a sign that a serious medical condition is present. A call to the adult's primary care physician is recommended in order to obtain a diagnosis as well as the necessary medications for lowering the fever.

Low-Grade Fever Concerns

Contrary to popular belief, a temperature does not have to be high to be dangerous. In fact, a low-grade fever can be just as serious, especially if it persists for several weeks. The Mayo Clinic explains that a low-grade fever can indicate something as simple as an infection in the urinary tract or an illness that is more severe. Lymphomas and other types of cancers can manifest as low-grade fevers, which can often be controlled with medications once the illness is revealed.

Symptomatic Concerns

The symptoms that accompany a fever can be just as dangerous as the fever itself. In fact, University of Virginia Health Systems reports that listlessness, abnormal breathing, rashes and a stiff neck should be addressed immediately by medical personnel. High fevers can also cause confusion and seizures in adults, which also require immediate medical attention.


Adults who travel outside of the United States should pay close attention to fevers that occur while they are out of the country and even those that manifest after they have returned home. For a recent traveller, a fever as low as 38.3 degrees C, can be dangerous. According to eMedicineHealth, travel outside the United States can expose an individual to a variety of toxins, diseases and bacterium that can cause illnesses that result in fever. Therefore, an adult who experiences a fever after travelling should seek medical attention immediately in order to determine the fever's root cause.