Read below about fever, including causes, treatment options and remedies. Or get a personalized analysis of your fever from our A.I. health assistant. At Buoy, we build tools that help you know what’s wrong right now and how to get the right care.

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Fever Symptoms

Headache? Chills? Fatigue? Uh-oh, you might just have a fever. A fever, even if it doesn't necessitate an immediate trip to the doctor (for most adults), does indicate something is definitely wrong in the body — from the flu to a cold, to something more serious [1,2].

This is because the body works very hard at maintaining homeostasis in all it processes, including body temperature, and when it cannot achieve that 98.6 degrees Fahrenheit like normal, there is always a reason. It's just that some reasons are more serious than others.

Fever symptoms are typically caused by other factors relating to the illness behind the fever and include:

With severe fever other symptoms may be present:

The hallmark sign of a fever is a temperature at or above 100.4 degrees Fahrenheit (38 degrees Celsius). Normal body temperature ranges from 97 to 99 degrees Fahrenheit (which is the same as 36.1-37.2 degrees Celsius).

Fever Causes Overview

Our body temperature is controlled in a way similar to the way that a thermostat regulates the temperature of a room. When a room cools below a set temperature, a sensor in the thermostat sends an electronic signal to the furnace to produce more heat. In much the same way, when our body temperature drops below normal, "sensors" in the hypothalamus (a gland in the brain) are triggered to increase body temperature [3]. One way the body increases temperature is by shivering.

Those same "sensors" can indicate that the body is too warm. Whether due to environmental conditions, such as working outside on a hot day, or pathologic conditions, such as fever, mechanisms (such as sweating) are put into action to lower body temperature.

Fever symptoms usually mean infection – commonly the flu, the common cold, or pneumonia. In fact, any significant infection will cause a fever. The infection, whether it be bacterial, viral, or from a parasite, causes the thermostat in the hypothalamus to reset. As body temperature rises, your immune system is stimulated to clear the infection.

In fact, an elevated body temperature (fever) is how our body protects us via the immune system as it combats our infection and "burns" it out of the body. Usually, this rise in body temperature helps us beat the infection.

Trauma, surgery, some cancers, certain types of nervous system injuries and some medications may also cause fever symptoms.

A.I. Health Assistant Causes for Fever

The list below shows results from the use of our A.I. Health Assistant by Buoy users who experienced fever. This list does not constitute medical advice.

  1. 1.Common Cold

    The common cold is a viral infection of the upper respiratory tract.

    The common cold resolves within 7 to 10 days.

    Top Symptoms:
    fatigue, headache, cough, sore throat, congestion
    Symptoms that never occur with common cold:
    being severely ill, severe muscle aches, rash, severe headache, sinus pain
  2. 2.Viral (Norovirus) Infection

    Noroviruses are a group of related viruses that leads to nausea, vomiting, diarrhea, and cramps. These viruses cause gastroenteritis, an inflammation of the stomach and intestines. When the diarrhea and/or vomiting is severe, dehydration can occur. Symptoms of dehydration include a dry mouth, dizziness, urinating less frequently and dark urine.

    Usually resolves within 2-3 days.

    Top Symptoms:
    diarrhea, vomiting or nausea, fatigue, nausea, abdominal pain (stomach ache), headache
    Symptoms that always occur with viral (norovirus) infection:
    diarrhea, vomiting or nausea
    Symptoms that never occur with viral (norovirus) infection:
    severe abdominal pain, throbbing headache, severe headache, tarry stool, vaginal bleeding, alertness level change
  3. 3.Influenza

    Influenza, or Flu, is an infection of the airway caused by the flu virus, which passes through the air and enters the body through the nose or mouth. The symptoms are similar to those of a cold, but the flu is usually more serious.

    Most recover within 1 week but cough and malaise can persist for 2 weeks.

    Top Symptoms:
    fatigue, headache, loss of appetite, cough, muscle aches
    Symptoms that never occur with influenza:
    headache resulting from a head injury
    Phone call or in-person visit
  4. 4.Viral Throat Infection

    Viral pharyngitis is an inflammation of the pharynx, the part of the throat between the nasal cavity and mouth, which causes throat pain.

    Symptoms generally resolve within 3-4 days

    Top Symptoms:
    sore throat, cough, congestion, fever, hoarse voice
    Symptoms that always occur with viral throat infection:
    sore throat
    Symptoms that never occur with viral throat infection:
    being severely ill
  5. 5.Viral Pneumonia

    Viral pneumonia is inflammation (irritation and swelling) of the lungs due to infection with a virus. Community-acquired pneumonia is the most common type, which is usually acquired in public areas such as at work, school, or grocery store.

    Symptoms begin to improve within a few days.

    Top Symptoms:
    fatigue, headache, cough, shortness of breath, loss of appetite
    Primary care doctor

    Fever Checker

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  6. 6.Mononucleosis Infection

    EBV Mononucleosis is a clinical syndrome characterized by fever, sore throat, and swollen lymph nodes.

    2-3 weeks

    Top Symptoms:
    fatigue, headache, loss of appetite, abdominal pain (stomach ache), cough
    Primary care doctor
  7. 7.Bacterial Pneumonia

    Bacterial pneumonia is the infection of the lungs with bacteria (as opposed to a fungus or a virus).

    1-3 weeks

    Top Symptoms:
    fatigue, cough, headache, loss of appetite, shortness of breath
    Symptoms that always occur with bacterial pneumonia:
    In-person visit
  8. 8.Strep Throat Requiring Throat Swab

    Strep throat is a bacterial throat infection that can make the throat feel sore and scratchy. Only a small portion of sore throats are the result of strep throat. And, if you do not show enough signs of a true strep throat, testing may be needed before treatment is begun.

    1-3 days with treatment

    Top Symptoms:
    fatigue, nausea, sore throat, fever, rash
    Symptoms that always occur with strep throat requiring throat swab:
    sore throat
    Symptoms that never occur with strep throat requiring throat swab:
    general weakness
    Primary care doctor
  9. 9.Acute Bacterial Sinusitis

    Acute bacterial sinusitis occurs when the sinuses become infected and, in turn, inflamed, which causes pain and other symptoms. The sinuses are air-filled cavities in the face that are generally clean and empty but when they're sick collect excess mucus and can become infected. When your symptoms are persisting for 10 days or more or are getting worse over time, it's more likely that you'll have a bacterial infection as compared to a viral infection.

    7-15 days

    Top Symptoms:
    fatigue, headache, cough, sinusitis symptoms, muscle aches
    Symptoms that always occur with acute bacterial sinusitis:
    sinusitis symptoms
    Symptoms that never occur with acute bacterial sinusitis:
    clear runny nose, being severely ill
    Primary care doctor
  10. 10.Urinary Tract Infection

    In women, the opening to the urethra (the tube that carries urine from the bladder to the outside of the body) is very close to the anus, and bacteria from the anus can easily escape and travel up the urethra. These bacteria can infect the bladder, and cause what is known as a urinary tract infection (UTI).

    Symptoms most often go away within 24 to 48 hours after treatment begins.

    Top Symptoms:
    abdominal cramps (stomach cramps), pelvis pain, sudden urgency to urinate, signs of urinary tract inflammation, urinary changes
    Symptoms that always occur with urinary tract infection:
    signs of urinary tract inflammation
    Phone call or in-person visit

Fever Treatments and Relief

Doctors typically agree that mild fevers require no effort to bring the fever down or necessitate a trip to a hospital. In fact, leaving the fever alone helps the body continue to fight the infection causing the fever [4].

The fever is helping the body to kill the viruses and infectious bacteria that is causing the fever.

For taking your temperature, know that temperature can be measured with several types of thermometers. There are oral, rectal, ear, forehead, and underarm thermometers. Although oral and rectal temperatures are the most accurate, ear, forehead and underarm temperatures are the easiest to take (especially with infants/children). It is normal for an oral or rectal temperature to be a bit higher than one taken from the ear, forehead or underarm. It is important to wait at least 30 minutes after eating or drinking anything before taking an oral temperature.

The following medications can help to lower a fever if necessary:

  • Aspirin (should not be given to children or pregnant women)
  • Acetaminophen
  • Aspirin and acetaminophen taken together are more effective than either taken alone
  • Ibuprofen
  • Naproxen
  • Corticosteroids (as prescribed by a healthcare provider)

Overall, getting adequate rest and drinking plenty of fluids is the best approach to most fevers.

Seek professional care immediately if you have fever and:

  • Are pregnant
  • Are having hallucinations or seizures
  • Your temperature does not go down even after taking a fever-reducing medication
  • Have recently traveled abroad, especially to resource-poor areas
  • Have recently had surgery
  • Have a fever that lasts for more than three days
  • Have a chronic medical condition such as diabetes, cancer or sickle cell disease
  • Have a weakened immune system
  • Think you may have recently been bitten by a tick
  • Your temperature is more than 104 degrees Fahrenheit
  • Are experiencing confusion, rash, persistent vomiting or diarrhea, problems breathing, severe neck or head pain, or severe abdominal pain.

FAQs About Fever

Here are some frequently asked questions about fever.

What is considered a fever?

In adults, a fever is a temperature higher that 38.2 degrees Celsius or 100.4 degrees Fahrenheit. A fever is caused by "pyrogens," pyro meaning heat or fire, and gen, meaning the creation of substances that create heat. Pyrogens are often foreign substances that the body recognizes as dangerous. In response, the body raises the temperature to impair the functioning of those compounds throughout the body.

What is a bad (high-grade) fever?

A high grade fever is commonly described at 39.4 degrees Celsius or 103 degrees Fahrenheit. At more than 104 degrees Fahrenheit, it is often necessary to seek medical attention immediately. A fever is caused by the hypothalamus (the thermostat of the body) setting a new base temperature. The body, because the body now believes its temperature should be five, 10, or 15 degrees higher than normal, feels cold — relatively speaking. This causes chills, the impulse to bundle up, shivering, and (as blood vessels constrict to keep warm blood near the chest and abdomen) cold hands and feet.

What causes low grade fever?

Fevers, low and high grade fevers, are caused most commonly by infection. The body is able to tolerate higher temperatures than the microbes infecting it. The body elevates its temperature to a range wherein microbes are unable to function, but the body is still functional. When the microbes are no longer functioning, the fever resolves.

Why do we get fevers?(same as previous)

Fevers are our body's defense mechanism. They are a means of raising the body temperature to an extent that pathogens (bacteria and viruses) and the cells they invade do not function as well as they have in the past. We get fevers primarily ro raise our body temperature which may interfere with the function of pathogens within the body and give our immune cells a competitive edge.

How long is too long to have a fever?

Most common colds and illnesses last for 7–10 days. In the presence of symptoms like a cough, sore throat, or runny nose, a fever should last no longer than the symptoms, and usually lasts for 3–4 days during each cold. If an individual has a fever in the absence of symptoms for longer than three weeks, it is called a fever of unknown origin and that individual should seek care.

Questions Your Doctor May Ask About Fever

  • Q.Have you been feeling more tired than usual, lethargic or fatigued despite sleeping a normal amount?
  • Q.Have you experienced any nausea?
  • Q.Do you have a cough?
  • Q.Are you experiencing a headache?

If you've answered yes to one or more of these questions, try our fever symptom checker to find out more.

Fever Quiz

Fever Symptom Checker Statistics

  • People who have experienced fever have also experienced:

    • 8% Chills
    • 6% Headache
    • 6% Abdominal Pain (Stomach Ache)
  • People who have experienced fever had symptoms persist for:

    • 45% Less Than a Week
    • 42% Less Than a Day
    • 5% One to Two Weeks
  • People who have experienced fever were most often matched with:

    • 50% Influenza
    • 25% Common Cold
    • 25% Viral (Norovirus) Infection
  • Source: Aggregated and anonymized results from visits to the Buoy AI health assistant (check it out by clicking on “Take Quiz”).

A.I. Health Assistant

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  1. Kaneshiro NK. Fever. U.S. National Library of Medicine: MedlinePlus. Updated December 3, 2018. MedlinePlus Link.
  2. Informed Health Online [Internet]. Cologne, Germany: Institute for Quality and Efficiency in Health Care (IQWiG); 2006. Fever in Children: Overview. Updated Nov 17, 2016. NCBI Link.
  3. Informed Health Online [Internet]. Cologne, Germany: Institute for Quality and Efficiency in Health Care (IQWiG); 2006. How is Body Temperature Regulated and What is Fever? Updated Nov 17, 2016. NCBI Link.
  4. Ray JJ, Schulman CI. Fever: Suppress or Let It Ride? Journal of Thoracic Disease? 2015;7(12):E633-E636. NCBI Link.
  5. Consolini DM. Fever in Infants and Children. Merck Manual Consumer Version. Updated July 2018. Merck Manual Consumer Version Link.