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What is fever?

Fever is an increase in your body’s temperature to a range that is above normal (98.6 degrees Fahrenheit). Normal body temperature can change throughout the day by a few degrees. Various factors can increase your body temperature including infection, eating, physical activity, medications, surrounding (room or outdoor) temperature, or a strong emotional response.

An oral temperature of 99.5 degrees Fahrenheit in a child and over 99 to 99.5 degrees Fahrenheit in adults is considered a fever. Fever can be caused by fairly benign conditions, such as a cold, or by serious conditions, such as influenza and meningitis. Infant teething, recent immunization, autoimmune and inflammatory disorders, and some cancers can cause a fever as well.

An extremely high fever can lead to seizures (called a febrile seizure) in children. These seizures do not usually cause permanent harm, but you should visit your health care professional if your child experiences a seizure. Seek emergency care if a seizure lasts more than a couple of minutes.

If your fever lasts more than 48 hours, is associated with other alarming signs, or causes you concern, seek prompt medical care. Fever in infants and very young children can quickly become serious, so exercise caution if your baby develops a fever. Seek immediate medical care (call 911) if you, or someone you are with, have a fever with excessive crying, difficulty breathing, stiff neck, or confusion. These are signs of a serious or life-threatening illness that should be immediately evaluated in an emergency setting.


What other symptoms might occur with fever?

Fever may be accompanied by other symptoms, depending on the underlying disease, disorder or condition. Fever is usually a sign of infection, which often leads to a variety of symptoms. This section describes relatively common as well as more serious symptoms that may accompany a fever.

Symptoms may occur along with fever

Fever may occur with other common symptoms including:

    Serious symptoms that might indicate a life-threatening condition

    In some cases, fever may occur with other symptoms and certain combinations of symptoms that might indicate a serious or life-threatening condition that should be immediately evaluated in an emergency setting. Be particularly concerned about fever in infants two months of age or younger. Seek immediate medical care (call 911) if you, or someone you are with, have any of these life-threatening symptoms:

    • Bluish coloration of the lips or fingernails

    • Change in level of consciousness or alertness, such as passing out or unresponsiveness

    • Change in mental status or sudden behavior change, such as confusion, delirium, lethargy, hallucinations and delusions

    • Crying inconsolably

    • Extremely watery diarrhea, possibly with blood

    • High fever (higher than 101 degrees Fahrenheit)

    • Respiratory or breathing problems, such as shortness of breath, difficulty breathing, labored breathing, wheezing, not breathing, and choking

    • Seizure

    • Stiff neck with nausea or vomiting and possible confusion

    • Very bad headache


    What causes fever?

    Multiple types of infections, inflammatory disorders, and conditions can lead to a fever. More common infections include flu (influenza), pneumonia, appendicitis, and urinary tract infections. Rheumatoid arthritis and other connective tissue inflammatory conditions can also be present with a fever. Your baby may even have a fever when teething. Because there are so many possibilities, it is important to contact your doctor to address your concerns and answer your questions.

    Possible causes of fever

    Fever is a sign of many different types of infections:

    Other causes of fever

    Fever can also be caused by inflammatory conditions including:

    Life-threatening causes of fever

    In some cases, fever may be a symptom of a serious or life-threatening condition that should be immediately evaluated in an emergency setting. These conditions include:

    • Brain abscess

    • Epiglottitis (life-threatening inflammation and swelling of the epiglottis, a tissue flap between the tongue and windpipe)

    • Influenza, particularly in the very old or young

    • Liver abscess

    • Meningitis (infection or inflammation of the sac around the brain and spinal cord)

    • Pericarditis

    • Pneumonia

    • Septic shock

    • Tuberculosis (serious infection affecting the lungs and other organs)

    Questions for diagnosing the cause of fever

    To diagnose the underlying cause of fever, your doctor or licensed health care practitioner will ask you several questions related to your symptoms. Questions for diagnosing the cause of fever include:

    • When did the fever start?

    • How long have you had a fever?

    • Is the fever constant or intermittent?

    • Is the fever reduced by common over-the-counter medications, such as acetaminophen (Tylenol)?

    • Do you have any other symptoms, such as a cough or sore throat?

    What are the potential complications of fever?

    A rise in temperature is your body’s natural way of killing the infectious agent or preventing its spread. A fever is a sign of an infectious or inflammatory process, many of which can be treated without serious difficulties. In most cases, the complications are due to the underlying problem, not the fever itself. However, there are potential complications of untreated or poorly controlled fever, some of which can be serious and even life threatening including:

    • Brain damage from an extremely high fever

    • Dehydration due a decreased desire to drink fluids

    • Dehydration due to vomiting or diarrhea

    • Long term physical disability

    Was this helpful?
    Medical Reviewer: William C. Lloyd III, MD, FACS
    Last Review Date: 2018 Nov 25
    1. Fever. Medline Plus, a service of the National Library of Medicine National Institutes of Health. http://www.nlm.nih.gov/medlineplus/ency/article/003090.htm
    2. Fever. FamilyDoctor.org. http://familydoctor.org/online/famdocen/home/tools/symptom/503.html
    3. Collins RD. Differential Diagnosis in Primary Care, 5th ed. Philadelphia: Lippincott, Williams & Williams, 2012.
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