A fever is a part of the body’s protective response to illness. When certain pathogens, such as bacteria and viruses, enter the body, the immune system signals the body to increase its temperature in an attempt to destroy them.
However, severe illness can cause the mechanisms that maintain a normal body temperature to go awry, and the results can lead to extremely high temperatures that can be life-threatening.
This article will discuss how a fever affects an adult’s body and when it is cause for concern.
If a person is concerned about a fever or how they feel overall, they should talk to a doctor.
As a general rule, adults should consider seeking medical attention if their temperature reaches above 104 °F (40°C). Doctors consider this temperature to be a high-grade fever.
However, a fever is not the only symptom a person has when they are ill. A person should consider other symptoms, such as vomiting, breathing issues, confusion, or how they feel overall when deciding whether they need medical attention.
Doctors categorize a fever by the reading on the thermometer, how long the fever lasts, and whether it keeps going up and down.
Normal body temperature can fluctuate. According to a 2019 systematic review, typical body temperatures vary according to a person’s age, and whether they take their temperature orally or rectally. The table below indicates a range of normal body temperatures.
|Ages||Oral °F (°C)||Rectal °F (°C)|
|Mean temperature||97.8 (36.5)||98.6 (37.0)|
|Less than 60 years of age||98.1 (36.7)||98.8 (37.1)|
|Over 60 years of age||97.5 (36.4)||98.6 (37.0)|
It is important to note that temperatures can fluctuate. A normal rectal body temperature ranges from 98.6–100.4°F.
The following are the classifications of body temperature ranges, according to an article in the Journal of Infection and Public Health:
- Mild or low-grade fever: 100.4–102.2°F (38–39°C)
- Moderate grade fever: 102.2–104.0°F (39°C–40°C)
- High-grade fever: 104.1–106.0°F (40°C–41.1°C)
These temperature values are rectal measurements, which doctors consider the most accurate.
However, the article also emphasizes that doctors can better diagnose a person’s condition by considering their other symptoms rather than the severity of their temperature.
Sustained or continuous fever
A sustained fever is when a person has a temperature above normal that does not fluctuate by more than 1.5°F (1°C) for 24 hours.
Causes may include:
- Gram-negative bacteria: These are bacteria that can cause pneumonia, bloodstream infections, and surgical site infections.
- Typhoid: Typhoid is a bacterial infection that can cause fever.
- Acute bacterial meningitis: This is a severe infection that requires emergency medical help.
- Urinary tract infection (UTI): Cystitis is an infection of the bladder, and urethritis is an infection of the urethra.
An intermittent fever occurs when a person experiences a raised temperature for several hours a day. The temperature then goes back to normal before spiking again.
Common causes may include:
- Malaria: This is an infection that some mosquitoes transmit.
- Tuberculosis (TB): This is an infection of the lungs.
- Lymphoma: This is a form of cancer that begins in the cells.
- Sepsis: This occurs when the body has an extreme reaction to an infection.
This is a daily fever that is always higher than normal but may fluctuate as much as 3.6°F (2°C) throughout the day.
Common causes may include:
- Infective endocarditis: This is an infection of the endocardium, which is the membrane that lines the inside of the heart.
- Rickettsiae infections: This is an infection transmitted by ticks, mites, and lice.
People who experience an internal temperature of 104°F (40°C) and higher for prolonged periods can develop hyperthermia. For this reason, it is essential to try to keep a fever from becoming too high.
Potential complications from a high-grade fever can include:
A high-grade fever can also cause cognitive dysfunction, which affects a person’s memory, comprehension, reasoning, and problem-solving ability. Some people may also have difficulty paying attention.
Typically, these symptoms are only temporary, and most people recover. However, in extreme circumstances, some people experience permanent changes.
Fever is a common symptom of the novel coronavirus, known as COVID-19.
According to a study published in the New England Journal of Medicine in February 2020, data on 1,099 people in China who had COVID-19 showed that 43.8% had a fever on admission to the hospital. An estimated 88.7% developed a fever during their hospitalization.
The authors defined a fever as an axillary (armpit) temperature of 99.8°F (37.7°C) or higher.
Other symptoms include:
- a cough
- shortness of breath
If a person suspects they may have COVID-19, they should call a doctor or health department for further testing.
For live updates on the latest developments regarding the novel coronavirus and COVID-19, click here.
A low-grade fever can be the body’s protective measure. Scientists are still in debate whether a person should treat a low-grade fever.
However, if a person does have a fever or does not feel well, they could take fever-reducing medications, such as:
As a fever is typically a symptom of another condition, a person may require different treatments depending on the cause.
If a person has an underlying bacterial illness, a doctor may prescribe antibiotics. These can treat the infection, which can help reduce fever.
Other steps a person can take to make themselves more comfortable include resting, drinking plenty of fluids, wearing loose clothing, and taking cool or lukewarm baths.
There are some steps a person can take to help prevent getting a fever:
- Always cover the mouth and nose when sneezing and wash hands immediately after sneezing or coughing.
- Refrain from sharing personal items, such as utensils, cups, and even toothbrushes.
- Try not to touch the face. A person can easily transmit the pathogen from their face to their nose or mouth, which might allow the germs to enter the body.
- Avoid contact with people who are sick. This can help prevent the transmission of illness.
- Maintain good hygiene. Washing hands may help prevent bacteria and viruses from spreading.
A fever is a protective mechanism for the body as the immune system works to fight against illness in a variety of ways.
If a person feels very unwell in addition to having a fever or they are already immunocompromised due to pre-existing conditions, they should seek medical attention.
A person should also see their doctor if they have tried to control their fever at home, but over-the-counter medicines and other treatments are ineffective.
A fever can become dangerous if it reaches 104°F (40°C) or higher.