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What causes fever? 221 possible conditions


Fever is also known as hyperthermia, pyrexia, or simply elevated temperature. It describes a body temperature that is higher than normal. Fever can affect children and adults alike. A short-term increase in body temperature can help the body fight off illness. However, a severe fever can be a medical emergency.

Recognizing a fever can facilitate treatment and proper monitoring of the symptom. According to the Mayo Clinic, normal body temperature is typically 37 degrees C, or 98.6 degrees F. What is considered a normal body temperature in each person varies slightly (Mayo Clinic, 2011).

According to the National Institutes of Health (NIH), a child has a fever when a temperature taken orally is higher than 99.5 degrees F, or 37.5 degrees C. An adult likely has a fever when body temperature exceeds 99 to 99.5 degrees F, or 37.2 to 37.5 degrees C. Normal body temperature can vary slightly depending on the time of day (NIH, 2010).

What Usually Causes Fevers?

Some reasons for a fever are:

  • infections, including pneumonia, colds, flu, ear infections, and bronchitis
  • recent immunization (children)
  • teething in children
  • certain inflammatory diseases or autoimmune disorders, including rheumatoid arthritis and Crohn’s disease
  • cancer
  • blood clots
  • certain medicines

How to Treat a Fever at Home

Home care for a fever depends on how severe it is. A mild fever with no other symptoms does not typically require medical treatment. Drinking fluids and making an effort to rest are usually enough.

Take measures at home to address elevated body temperature. This is especially true if fever is accompanied by general discomfort, dehydration, difficulty sleeping, or vomiting. Home care measures include:

  • Make sure the room temperature where the person is resting is comfortable.
  • Take a regular bath or a sponge bath using lukewarm water.
  • Take acetaminophen and/or ibuprofen (or give these medications to your child in appropriate doses).
  • Take aspirin (which is for adults only, unless a doctor has given you different advice).
  • Drink plenty of fluids.

When to See a Doctor About a Fever

A mild fever can typically be treated at home. However, according to the NIH, there are some instances when you or your child should see a doctor as soon as possible. These instances include when (NIH, 2010):

  • a child’s temperature is at least 100.4 degrees F, or 38 degrees C when taken rectally (under 3 months of age)
  • a child’s body temperature is higher than 102.2 degrees F, or 39 degrees C (between 3 months and 1 year of age)
  • an adult’s body temperature is higher than 103 degrees F, or 39.4 degrees C
  • body temperature is higher than 105 degrees F, or 40.5 degrees C, and at-home treatment do not bring it down and/or it’s causing discomfort (older children and adults)
  • a child has other symptoms of illness, such as a cough or a sore throat
  • a child or adult has a serious medical illness and/or a compromised immune system
  • the fever is not going away (one to two days for children under 2, and two to three days for older children and adults)
  • a child recently had one or more immunizations
  • the fever comes and goes for at least a week
  • the person experiencing a fever has recently been in a developing country
  • the person has new rashes or bruises
  • the person is having pain during urination

Your physician will probably perform a physical examination and medical tests. This will help him or her determine the cause of the fever and an effective course of treatment.

When Is Fever a Medical Emergency?

Go to the nearest emergency room or call 911 if you or your child is experiencing any of the following:

  • inconsolable crying (children)
  • confusion
  • inability to walk
  • trouble breathing
  • severe headache
  • stiff neck
  • seizure

How Can Fever Be Prevented?

Limiting exposure to infectious agents is one of the best ways to prevent a fever. Infectious agents often cause body temperature to rise. Wash your hands regularly and keep hands away from the nose, mouth, and eye area.

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See a list of possible causes in order from the most common to the least.


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Strep Throat

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Chronic Bronchitis

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Fever of Unknown Origin

Fever of unknown origin (FUO) refers to the elevation in body temperature for a specified time, for which a cause is not found after basic medical evaluation.

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Acute HIV Infection

Acute HIV infection is the primary stage of infection by the human immunodeficiency virus. There are several telltale symptoms, one of which is a rash.

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RSV (Respiratory Syncytial Virus) Infection

Respiratory syncytial virus, or RSV, is a common virus that causes infections of the lungs and airways. Common symptoms include fever, wheezing, and bluish skin from oxygen deprivation.

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Dengue Fever

Dengue fever is a disease that affects much of the tropical region and is caused by one of four dengue viruses. A skin rash between two and five days after the initial fever is a common symptom.

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Food Poisoning

This condition is considered a medical emergency. Urgent care may be required.

Food poisoning occurs when you consume foods contaminated with bacteria, viruses, or parasites. Symptoms are usually uncomfortable but not severe.

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Non-Hodgkin’s Lymphoma

Non-Hodgkin's lymphoma is a lymphatic system cancer. Symptoms may include swollen lymph nodes, chest pain, fatigue, and fever.

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Lung Cancer Overview

Lung cancer is a cancer that originates in the lungs. Lung cancer often goes undetected in the early stages, since symptoms don't usually present themselves until the advanced stages of the disease.

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Sinus Infections (Sinusitis)

A sinus infection causes the sinuses and nasal passages to become inflamed. Facial swelling is a common sign of this type of infection.

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Septic Shock

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Bone Infection (Osteomyelitis)

A bone infection may occur when bacteria or fungi invade the bone, causing many symptoms, including fever, redness, stiffness, and swelling.

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Alcoholic Liver Disease

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Caffeine Overdose

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Heat Emergencies

This condition is considered a medical emergency. Urgent care may be required.

Heat emergencies are health crises caused by exposure to hot weather and sun. Heat emergencies have three stages: heat cramps, heat exhaustion, and heatstroke. All three stages are serious.

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Middle Ear Infection

A middle ear infection (otitis media), occurs when a virus or bacteria causes the area behind the eardrum to become inflamed. It is most common in children.

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This feature is for informational purposes only and should not be used to diagnose.
Please consult a healthcare professional if you have health concerns.