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What Causes Fever And The Possible Underlying Conditions

Medically reviewed by Janie-Vi Villamor Ismael-Gorospe, MD · General Practitioner

Written by Honey Buenaventura · Updated Mar 14, 2022

    What Causes Fever And The Possible Underlying Conditions

    What causes fever? A fever may be a temporary increase in your body temperature, often thanks to an illness. Having a fever may be a signal that there is an infection and your body is fighting it off. For an adult, a fever could also be quite uncomfortable, but usually isn’t a cause for concern unless your temperature reaches 103 F (39.4 C) or higher.

    Children get a fever from time to time. Fever in itself typically will not necessarily bring bodily harm and may actually be a good thing as it signifies that our own body is fighting off an infection.

    Here’s more about fevers, what causes fever, and some underlying conditions that may be the possible root of them.

    What is a fever?

    A fever often happens when the body’s internal temperature raises the blood heat above its acceptable levels. A person’s hypothalamus is the regulator and knows what temperature your body should be, which is on average,  98.6°F or 37°C. The hypothalamus sends information to your whole body to help normalize the temperature to remain that way.

    The following readings on a thermometer generally indicate a fever:

  • Rectal, ear or temporal artery temp: 100.4 (38 C) or higher
  • Oral temp: 100 F (37.8 C) or higher
  • Armpit temp: 99 F (37.2 C) or higher
  • Most individuals’ body temperatures fluctuate and change during the course of the day. It is often slightly lower within the early part of the day and slightly higher during nighttime, and can vary with kids as they run around, jump, and play.

    There are instances when the hypothalamus will just have to regulate, to increase or even decrease, the body temp. The body responds via fluctuating temperature in response to an infection, illness, or an external cause. Why? Doctors believe that increasing the warmth may be a way for our body to defend itself against germs that cause infections, making it an uninviting place for them.

    What causes fever?

    It’s important to remember that fever by itself isn’t an illness — it is often a symptom of another problem.

    Fevers are often caused by a couple of things, including viruses and bacteria. Fevers also usually occur when the body responds to immunization

    When is fever a sign of something serious?

    Children who have body temperatures less than 102°F or 38.9°C more often than not do not need medication unless they are irritated and uncomfortable.  

    If your child is around 3 months and 3 years old and has a fever of 102.2°F or 39°C and up, call a doctor and ask if you need to bring your child to be examined further.

    A fever with a temperature higher than 100.4 F (38.0 C) in a child might cause seizures.

    Diagnosing the cause of a fever

    To help diagnose fever properly, your doctor will ask you about:

    • Other symptoms such as coughing, abdominal pain, vomiting, diarrhea, or pain when urinating
    • Recent surgeries or injuries
    • Recent vaccinations
    • New drugs you may be taking
    • Recent travel, particularly abroad

    Treating a fever

    Remember that fever is your body’s defense against infection-causing viruses, bacteria, and germs. In it by itself, a fever is generally harmless, though a high-temperature fever can be pretty miserable.

    These are just some simple steps that may help you feel better:

    1. Drink plenty of fluids to help cool your body and prevent dehydration.
    2. Take a warm bath and use a damp washcloth on your forehead and wrists.
    3. Dress in light, cool, cotton (even if you have chills).  
    4. Eat light foods that are easy to digest.
    5. Take ibuprofen (Advil, Motrin, or others), naproxen (Aleve, Naprosyn, or others), acetaminophen (Tylenol, others), or aspirin to help relieve head and body aches and lower your temperature.
    6. Get plenty of rest.

    If you have a body temperature of over 104°F (40°C), call your doctor as soon as possible. Also, inform your doctor immediately if you have a fever along with any of these symptoms:

    • Seizure
    • Loss of consciousness
    • Vaginal discharge that is discolored or smells bad
    • Confusion
    • Severe pain anywhere in the body
    • Swelling or inflammation of any part of the body
    • Pain when urinating or urine that smells bad
    • Stiff neck
    • Trouble breathing

    For any concerns, consult your doctor

    Learn more about Symptoms here


    Hello Health Group does not provide medical advice, diagnosis or treatment.

    Medically reviewed by

    Janie-Vi Villamor Ismael-Gorospe, MD

    General Practitioner

    Written by Honey Buenaventura · Updated Mar 14, 2022

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