High Fever: Possible Causes and Treatments

Medically Reviewed By Carissa Stephens, R.N., CCRN, CPN
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A high fever is when body temperature rises above 103ºF (39ºC) in an adult or above 101ºF (38ºC) in a child. There are many causes of a high fever, including common conditions such as a sore throat, sinusitis, and urinary tract infections (UTIs). Some causes may be more serious and require immediate medical care. A fever this high may indicate the presence of a serious infection that has triggered your immune system. Very rarely, this immune response can result in a fever high enough to cause permanent harm or even life threatening complications due to overheating.

In rare cases, a high fever can occur without any infection as a result of arthritis, lupus, or certain gastrointestinal and vascular disorders.

This article reviews possible causes of a high fever, how this symptom differs in adults vs. children, and treatments for high fever.

Infection

Most bacteria that affect humans flourish in normal or near normal body temperatures. When you have an infection, your immune system raises your body’s temperature to stifle the growth of the invading microorganisms.

Both viral and bacterial infections can cause a high fever. Infections with a high fever as a symptom include:

Other symptoms

Your doctor will evaluate all of your symptoms to determine the specific infection that may be causing your high fever. Other symptoms that may indicate an infection and may occur with a high fever include:

Contact your doctor if you have any symptoms of infection, particularly if you have recently undergone surgery or have a weakened immune system. Prompt diagnosis and treatment can prevent complications that can become serious or life threatening.

Heat exhaustion

Teenager lying on back on cement steps in hot sun
Marco Govel/Stocksy United

Heat exhaustion occurs when your body temperature rises and your body is not able to cool itself quickly. You may develop heat exhaustion from working or exercising in hot temperatures, particularly if you do not drink enough water.

On its own, heat exhaustion is usually not serious. However, it can lead to heat stroke, which is a life threatening medical emergency.

Other symptoms

Symptoms of heat exhaustion include a fever of 101ºF (38ºC) or higher. Other symptoms may include:

Children under 4 years and adults over 65 years have a higher risk of heat-related illness. Talk with your doctor or your child’s pediatrician about steps to reduce the risk of heat exhaustion.

Learn steps to treat heat exhaustion here.

Sepsis

Sepsis is a systemic immune system reaction in response to an infection. Without treatment, sepsis can progress to septic shock. This is a life threatening condition that causes organ damage due to severely low blood pressure.

Sepsis can cause a body temperature that is very high or very low.

Other symptoms

The Sepsis Alliance uses the acronym “TIME” to identify the symptoms of sepsis.

Ttemperature that is higher (100ºF or 37.7ºC) or lower than usual
Iinfection symptoms that affect the whole body, such as fatigue or pain
Mmental status change, including confusion or extreme sleepiness
Eextremely ill feeling, which some people describe as the worst they have ever felt

Learn more about sepsis causes, stages, and treatments.

Drug reaction

Certain medications can cause a high fever as a side effect, known as a drug fever. In some cases, a fever may be the only adverse reaction a person experiences from a drug.

If you have an unexplained high fever, talk with your doctor or pharmacist about any medications you are taking. They can help determine if your fever is a side effect and discuss alternative treatment options if needed.

Noninfectious conditions

Several noninfectious conditions can cause a high fever as a symptom.

Your doctor will ask about all of your symptoms to help make an accurate diagnosis. If you already have a diagnosis, tell your doctor about any high fever or other symptoms you experience.

Noninfectious causes of a high fever include:

Fever of unknown origin

Fever of unknown origin (FUO) occurs when someone has had a fever for at least 3 weeks without a clear indication of the cause after a week of in-hospital evaluation.

Most times, doctors eventually identify an underlying cause, and it is typically an undiagnosed infection. In about 10% of adults with FUO, however, doctors are unable to determine the cause.

How is a high fever different in children?

Pediatricians have different guidelines related to fever for children based on their age.

Although there are several types of thermometers that parents and caregivers can use, doctors consider a rectal temperature to be the most accurate reading.

When evaluating fever in infants, doctors generally define a rectal temperature of 100.4ºF (38ºC) as clinically significant.

Newborns (0–3 months)

Any infant younger than 3 months who has a fever should receive medical care, even if they appear to have no other symptoms.

Infants at this age could be at high risk of infection or complications simply due to their age.

Young children (3 months to 3 years)

Guidelines from the American Academy of Family Physicians state that doctors should consider children in this age group to be at high risk if they have a fever along with symptoms including:

  • rapid breathing or difficulty breathing
  • difficulty waking or being roused from sleep
  • slow refill of color (more than 2 seconds) to the fingertips if pressed
  • petechiae, which is a rash of tiny spots that appear due to bleeding under the skin

School-aged children (3 years and older)

For children of this age, home care is typically effective in managing a fever. Management steps include:

  • allowing the child to rest
  • providing the child with plenty of fluids
  • giving the child acetaminophen or ibuprofen, following the dosage guidance on the label
  • keeping the child in light clothing
  • watching for symptoms of dehydration, such as a dry mouth or a lack of tears when crying

Febrile seizure

A febrile seizure is a seizure that occurs primarily in children due to a high fever. They are most common with fevers of 102ºF (38.9ºC) or higher, but they can occur with milder fevers as well.

Symptoms of a febrile seizure include:

  • stiffness
  • twitching
  • eye rolling
  • unresponsiveness
  • a change in skin color
  • changes in breathing

A febrile seizure typically lasts 1–2 minutes, and then the child quickly returns to their typical self.

Learn more about what to do if a child has a febrile seizure.

When should you contact a doctor for a high fever?

In many cases, a fever will go away on its own with home care. However, in some situations, a high fever requires prompt or even emergency medical care.

In children

Contact a doctor for a high fever if your child meets the following criteria.

AgeRectal temperatureAdditional symptoms
0–3 months100.4ºF (38ºC) or greaterChildren of this age with a fever should visit a doctor even if they have no other symptoms.
3 months to 3 years100.4ºF (38ºC) or greaterChildren of this age who have a fever for more than 3 days and who have additional symptoms should visit a doctor.
3 months to 3 years102ºF (38.9ºC) or greaterChildren of this age who have a fever of this level should visit a doctor even if they have no other symptoms.

Children of any age should visit a doctor if they experience:

  • a febrile seizure
  • recurrent fevers over a period of more than 7 days
  • a fever with a diagnosed chronic condition, such as cancer or lupus
  • a fever that occurs with a skin rash

In adults

Adults should seek medical attention for a high fever if they experience:

  • extreme thirst
  • reduced urine output
  • severe muscle cramps
  • lightheadedness
  • weakness
  • a fever after international travel
  • a fever with a diagnosed chronic condition, such as cancer or HIV
  • a fever with a weakened immune system

Heat exhaustion

Because heat exhaustion can progress to heat stroke, seek immediate medical care (call 911) for symptoms of heat exhaustion. You can provide first aid for someone with heat exhaustion by:

  • moving the person to a shaded or cooler area
  • giving the person frequent sips of cool water
  • removing unnecessary clothing, such as shoes and socks
  • applying cool compresses
  • having the person wash their face, neck, and head with cold water

Heat stroke

Symptoms of heat stroke in people of any age indicate a life threatening emergency. Call 911 for symptoms including:

  • a temperature of 106ºF (41ºC) or higher
  • a loss of consciousness
  • profuse sweating
  • hot, dry skin
  • seizures

What treatments are available for a high fever?

Treatment for a high fever often relies on treating the underlying cause.

Infection

For bacterial infections, treatment typically consists of antibiotics. Viral infections typically improve with time and home care, including rest, fluids, and over-the-counter (OTC) medications.

Sepsis

Sepsis can progress to septic shock, which is a life threatening emergency. Seek urgent medical care if you have symptoms of sepsis.

Rapid treatment for sepsis includes antibiotics to treat the underlying infection and medications that maintain blood flow to vital organs.

Drug reaction

If your fever is an adverse effect of a specific medication you are taking, your doctor can recommend alternative treatment options.

Frequently asked questions

These are some other questions that people often ask about high fevers. Lauren Castiello, M.S., AGNP-C, has reviewed the answers.

How long does the fever last with COVID-19?

Symptoms of COVID-19 can last from a few days to a few weeks, according to the Centers for Disease Control and Prevention (CDC). The CDC says that anyone with COVID-19 who has symptoms, including fever, should isolate for at least 5 full days. After this time, if you have been free from fever for 24 hours without needing fever-reducing medication, you can end your isolation.

Is drinking cold water good for fever?

Your body can become dehydrated when you have a fever, so drinking any kind of water is beneficial. Staying hydrated also helps your immune system fight off the infection causing the fever. Steps to cool yourself during a fever include wearing light clothing and taking OTC fever-reducing medications.

Summary

A high fever is a body temperate of 103ºF (39ºC) or higher in an adult. In a child, a temperature of 101ºF (38ºC) or higher is a high fever.

Causes of a high fever include infections, heat exhaustion, sepsis, and noninfectious conditions, particularly those that affect the immune system.

Contact a doctor if you or your child has a high fever, particularly if it occurs with other symptoms, including a loss of consciousness, confusion, or a rash.

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Medical Reviewer: Carissa Stephens, R.N., CCRN, CPN
Last Review Date: 2022 Jul 25
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