Fever

Overview

A fever is a temporary increase in body temperature above the normal range. Normal body temperature is about 98.6 F (37 C) but varies through the day and from person to person. A temperature of 100.4 F (38 C) or higher is generally considered a fever. Rather than being an illness itself, a fever is usually a sign that the body's immune system is responding to something, most often an infection.

Fevers are very common and are usually part of a normal, helpful immune response. Most are caused by viral or bacterial infections and resolve as the underlying illness clears. In adults and older children, a mild fever often does not need treatment beyond comfort measures. The level of concern depends more on how the person looks and feels and on accompanying symptoms than on the exact number, although very high fevers and certain warning signs, particularly in infants, need prompt medical attention.

Symptoms

Besides a raised temperature, a fever often comes with other symptoms as the body responds to illness.

• Feeling hot, flushed, or sweating
• Chills, shivering, and feeling cold despite a high temperature
• Headache and body or muscle aches
• Tiredness, weakness, and general feeling of being unwell
• Loss of appetite and increased thirst
• In young children, irritability or reduced activity

High fevers can sometimes cause confusion or, in some young children, brief seizures (febrile seizures). The presence of other symptoms, such as a stiff neck, rash, difficulty breathing, or severe pain, is often more important than the temperature itself in deciding how urgently to seek care.

Causes

Many conditions can raise body temperature, but infections are by far the most common cause.

• Viral infections: Colds, the flu, and many childhood illnesses.
• Bacterial infections: Such as strep throat, urinary tract infections, ear infections, and pneumonia.
• Other infections: Including some spread by insects or contaminated food and water.
• Non-infectious causes: Heat exhaustion or heatstroke, certain medications and vaccines, inflammatory conditions, and, less commonly, other illnesses.
• After immunization: A mild fever can follow some vaccines and is usually short-lived.

Risk Factors

• Exposure to infectious illnesses at home, school, or work
• Young age, especially infants and young children
• A weakened immune system
• Recent travel to areas with certain infections
• Recent surgery, medical procedures, or new medications
• Exposure to extreme heat

Diagnosis

A fever is confirmed by measuring body temperature, and evaluation focuses on finding the cause.

• Temperature measurement: Using a thermometer in the mouth, ear, forehead, armpit, or rectum (rectal readings are most accurate in infants).
• History and examination: Reviewing other symptoms, recent exposures, travel, and medications, and examining for a source of infection.
• Tests as needed: Depending on the situation, blood tests, urine tests, throat swabs, chest X-rays, or other studies may be used to identify the cause.

Treatment

Treatment addresses comfort and the underlying cause. A mild fever in an otherwise well adult or older child often needs no specific treatment.

• Fluids and rest: Drinking plenty of fluids prevents dehydration, and rest supports recovery.
• Fever-reducing medicine: Acetaminophen or ibuprofen can lower fever and ease aches and discomfort; follow dosing instructions and age guidance.
• Comfort measures: Light clothing, a comfortable room temperature, and lukewarm (not cold) sponging if desired.
• Treating the cause: Antibiotics are used only for bacterial infections; viral illnesses are managed supportively.

Do not give aspirin to children or teenagers because of the risk of a rare but serious condition. The goal of medication is comfort, and the temperature does not always need to be brought fully to normal.

Prevention

• Wash your hands often and well
• Stay up to date on recommended vaccines, including the yearly flu vaccine
• Avoid close contact with people who are sick
• Cover coughs and sneezes and avoid touching your face
• Prepare and store food safely and use clean water
• Take precautions against insect bites when traveling to certain areas

When to See a Doctor

See a doctor for a fever that lasts more than a few days, keeps rising, or comes with concerning symptoms. Seek emergency care for a stiff neck, severe headache, confusion, difficulty breathing, a rash that does not fade when pressed, chest pain, persistent vomiting, seizures, or signs of dehydration. Any fever in a baby under 3 months (100.4 F / 38 C or higher) is a medical emergency and needs immediate evaluation. A very high fever, a fever in someone with a weak immune system, or a fever after travel should also be assessed promptly.

Related Topics

Frequently Asked Questions

References

1. Mayo Clinic. Fever — Symptoms and causes.
2. MedlinePlus, U.S. National Library of Medicine. Fever.
3. Centers for Disease Control and Prevention (CDC).
4. American Academy of Pediatrics (AAP).