Fever occurs when your body temperature is elevated, often due to an illness. A fever is a response to inflammation and a reaction to foreign invaders in the body. A fever's purpose is to help the body fight off bacteria and viruses. Most fevers are treatable at home, but there are some that require medical attention.

While a body temperature of 99 to 100.3 degrees Fahrenheit is higher than normal, healthcare providers consider 100.4 F to be minimum that is called a fever.

This article covers the symptoms and types of fever, causes of fever, how to treat fever, and when to get help.

Woman with a fever

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Symptoms of Fever

In addition to a temperature at or above 100.4 F, a fever can also include the following symptoms:

  • Chills and shivers
  • Excessive sweating
  • Fatigue
  • Joint, bone, or back pain
  • Muscle aches
  • Headache
  • Dehydration

In children, symptoms of fever can include:

  • Lower activity levels and staying quiet
  • Fussiness
  • Increased thirst and less hunger
  • Feeling warm

For about 3% of children aged 6 months to 5 years old, seizures called febrile convulsions can occur with a fever. Children who experience febrile convulsions usually outgrow them by 5 years of age.

Causes of Fever

Fever is usually a result of the immune system's fighting off an infection. The most common causes of fever are:

Other causes of fever include:

  • Vaccinations, which can cause one to two days of mild fever in children
  • Autoimmune disorders like rheumatoid arthritis or lupus
  • Early stage cancer
  • Blood clots
  • Environmental heal stress

What Medications Cause Fever?

"Drug fever" is the term for fever that is a side effect of a medication. Drug fever usually disappears soon after the medication is discontinued.

Medications that could cause fever include:

  • Anti-seizure medications
  • H2-blockers, which reduce acid in the stomach
  • Antibiotics
  • Antihistamines

How to Treat Fever

Mild fevers are usually treated at home with:

  • Rest
  • Getting more fluids, which can include drinking soup broth or sucking on ice pops
  • Removing extra clothing or heavy blankets, especially for young children and infants
  • A lukewarm bath after medication

Medications to treat fever include:

  • Over-the-counter (OTC) fever-reducing medications like Tylenol (acetaminophen) or Advil (ibuprofen) taken as advised
  • Aspirin (for adults only)
  • Healthcare provider-approved medications for babies under 3 months of age

The treatment of the underlying cause of the fever will vary. Bacterial infections may be treated with antibiotics. Viral infections will not respond to antibiotics and may only receive treatment to relieve the symptoms, or antiviral medication may be used.

Complications and Risk Factors Associated with Fever

Fevers require medical attention if they're 100.4 F or higher in children aged 0 to 24 months or 103 F or higher in older children and adults. If left untreated, complications of fever could include:

  • Febrile seizures with higher fevers in young children (in 2% to 5% of children under age 5)
  • Brain damage with fevers of 107 degrees or higher
  • Breathing issues
  • Death

Are There Tests to Diagnose the Cause of Fever?

A healthcare provider will measure a person's vital signs (body temperature, breathing rate, heart rate, and blood pressure) and take their report of symptoms, medical history, and list of medications. They will perform a physical examination which will look for signs of inflammation and infection.

To further determine the illness that may be causing a fever, they may perform these tests:

The following tests may be performed:

  • Rapid tests for influenza, strep throat, COVID-19, and respiratory syncytial virus (RSV)
  • Blood tests: A complete blood count may show an increased white blood cell count in the case of an infection.
  • Urinalysis: The presence of white blood cells, bacteria, and blood may indicate a urinary tract infection.
  • Chest X-ray: This may show pneumonia or other infections of the lungs and airways.
  • Bacterial cultures: A sample from the site of suspected infection (urine, sputum, swab, blood, spinal fluid) may be cultured in the lab to look for bacterial invaders, identify them, and determine their antibiotic susceptibility.

When to See a Healthcare Provider

Call your healthcare provider if a child:

  • Is 3 months or younger and has a rectal temperature of 100.4 degrees or higher
  • Is 3 month olds to 12 month olds and has a fever of 102.2 degrees or higher
  • Is younger than 2 and has a fever lasting longer than 24 to 48 hours
  • Is older and has a fever lasting 48 to 72 hours
  • Has a weakened immune system
  • Has other symptoms like a sore throat, cough, or earache
  • Has recently been to another country

Adults should see a healthcare provider if they:

  • Have a fever over 105 degrees
  • Have a fever that lasts longer than 48 to 72 hours
  • Have new rashes or bruises
  • Have pain when urinating
  • Have a heart problem, lung problem, or sickle cell anemia
  • Have recently been to another country

Seek emergency medical attention for anyone of any age who has a fever and:

  • Can't walk
  • Seems confused
  • Can't be awakened easily (if at all)
  • Has blue lips, nails, or tongue
  • Has a seizure
  • Has breathing difficulty
  • Abdominal pain


Fever is a temporary rise in body temperature as it fights off an infection. In addition to a higher temperature, symptoms of fever can include chills, sweating, fatigue, and body pains. Causes of fever include bacterial or viral infections such as the flu or cold, overdressing, autoimmune disorders, and vaccinations. Some medications can also cause fevers.

Treating fever usually includes getting rest and drinking fluids while stabilizing body temperature with lighter clothes and blankets. OTC pain medications like acetaminophen and ibuprofen can also be a part of the treatment.

Frequently Asked Questions

  • Why do fevers occur?

    Fevers are usually a response to infections like bacteria or viruses. That's why they occur most often during illnesses like flu, cold, and pneumonia. Fevers can also be a part of autoimmune disorders like lupus or rheumatoid arthritis and conditions that weaken the immune system. At times, a high room temperature or intense emotions can also cause fever, as can medications, including antibiotics, antihistamines, and anti-seizure drugs.

  • When is a fever dangerous?

    While most fevers can be treated at home, some fevers can be dangerous. For babies younger than 3 months, a fever 100.4 degrees requires medical attention, while children 3 months old to 12 months old usually require medical attention at a fever of 102.2 degrees or higher. For adults or older children, a fever of 103 degrees or higher might require urgent care. A fever of any temperature that persists for a week is likely something that requires help from a healthcare provider.

  • What are the most effective ways to treat fever?

    Most fevers only require rest and fluids, however, over-the-counter medications can also help. Wearing lighter clothing and avoiding heavy blankets can also help with fever, as can a lukewarm bath after taking medication.

11 Sources
Verywell Health uses only high-quality sources, including peer-reviewed studies, to support the facts within our articles. Read our editorial process to learn more about how we fact-check and keep our content accurate, reliable, and trustworthy.
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By Neha Kashyap
Neha is a New York-based health journalist who has written for WebMD, ADDitude, HuffPost Life, and dailyRx News. Neha enjoys writing about mental health, elder care, innovative health care technologies, paying for health care, and simple measures that we all can take to work toward better health.