A fever is a rise in body temperature. It's usually a sign of infection. The fever itself is generally harmless and probably helpful. Fevers usually don't need treatment.

The average body temperature is 98.6 F (37 C). But normal body temperature can range between 97 (36.1) and 99 (37.2) or more. Your body temperature can vary depending on how active you are or the time of day. Generally, older people have lower body temperatures than younger people.

The following thermometer readings generally indicate a fever:

  • Rectal, ear or temporal artery temperature of 100.4 (38 C) or higher
  • Oral temperature of 100 F (37.8 C) or higher
  • Armpit temperature of 99 F (37.2 C) or higher

Should I treat a fever?

When you or your child is sick, the main goal is to relieve discomfort and promote rest. Treating a fever neither shortens nor particularly prolongs the course of an illness.

Treating fever in a child

Children with relatively high fevers may not look or act particularly sick. Treating a fever depends on the degree of discomfort. If your child is uncomfortable or restless, these home care strategies may help:

  • Encourage your child to drink fluids.
  • Dress your child in lightweight clothing.
  • If your child feels chilled, use a light blanket until the chills end.
  • Give your child acetaminophen (Tylenol, others) or ibuprofen (Advil, Children's Motrin, others) as directed on the label.

    Note these precautions:

    • Don't give aspirin to anyone age 18 or younger
    • Don't give ibuprofen to children under 6 months
    • Don't give acetaminophen to infants under 6 weeks

Treating fever in an adult

Treat adults with a fever based on how they look and feel. Adults with fevers of 103 F (39.4 C) or higher will generally look and act sick. Use the same home care strategies as listed for children.

When to seek medical advice

Get medical help for a fever if:

  • Your child is younger than 3 months and has a fever
  • Your child is age 3 to 6 months and has a temperature up to 102 F (38.9 C) and seems unusually irritable, lethargic or uncomfortable
  • Your child is age 3 to 6 months and has a temperature higher than 102 F (38.9 C)
  • Your child is age 6 to 24 months and has a temperature above 102 F (38.9 C) that lasts longer than a day but shows no other symptoms
  • Your child is 2 to 17 years and has a temperature up to 102 F (38.9 C) and seems unusually irritable, lethargic or uncomfortable
  • Your child is 2 to 17 years and has a temperature above 102 F (38.9 C) that lasts longer than three days or doesn't respond to medication
  • An adult has a fever that doesn't respond to medication, is consistently 103 F (39.4 C) or higher, or lasts longer than three days

When to seek emergency care

Seek emergency medical care if your child has a fever after being left in a hot car or other such potentially dangerous situation and shows any of these warning signs: 

  • Fever with no sweating
  • Severe headache
  • Seizures
  • Stiff neck
  • Confusion
  • Repeated vomiting or diarrhea
  • Irritability or significant discomfort
  • Any worrisome, different or unusual symptoms
Fahrenheit-Celsius conversion table
Fahrenheit Celsius
105 40.5
104 40.0
103 39.4
102 38.9
101 38.3
100 37.7
99 37.2
98 36.6
97 36.1
96 35.5

How to take a temperature

Always use a digital thermometer to check someone's temperature. Various types are available, including:

  • Digital thermometers, which can be used in the rectum (rectal), mouth (oral) or armpit (axillary), though an armpit reading is the least accurate
  • Digital ear thermometers (tympanic membrane)
  • Temporal artery thermometer, which measures the temperature of the temporal artery in the forehead

Because of the potential for mercury exposure or ingestion, glass mercury thermometers have been phased out and are no longer recommended.

No matter which type of thermometer you use, take these precautions when using it:

  • Read the instructions that came with the thermometer.
  • Clean it before and after each use with rubbing alcohol or soap and lukewarm water.
  • Don't use the same thermometer for both oral and rectal temperatures. Get two and label which is used where.
  • Never leave a child unattended while taking his or her temperature.

Rectal temperature (for infants)

  • Turn on the digital thermometer and dab petroleum jelly or another lubricant on the tip of the thermometer.
  • Lay the child on his or her stomach.
  • Carefully insert the tip 1/2 to 1 inch (1.3 to 2.5 centimeters) into the rectum.
  • Hold the thermometer and child still until the thermometer beep indicates it's done. To avoid injury, don't let go of the thermometer while it's inside the child.
  • Remove the thermometer and read the number.

Oral temperature

  • Turn on the digital thermometer. Place the thermometer tip under the tongue.
  • Close the mouth around the thermometer for the recommended amount of time or until the thermometer beep indicates it's done.
  • Remove the thermometer and read the number.

Armpit temperature

  • Turn on the digital thermometer. Place the thermometer under the armpit, making sure it touches skin, not clothing.
  • Hold the thermometer tightly in place until you hear the thermometer beep indicating it's done.
  • Remove the thermometer and read the number.

Ear temperature

  • Turn on the digital thermometer. Gently place it in the ear, no further than indicated by the instructions that came with the device.
  • Hold the thermometer tightly in place until you hear the thermometer beep indicating it's done.
  • Remove the thermometer and read the number.

Temporal artery temperature

  • Turn on the thermometer. Gently sweep it across the forehead and read the number.
April 15, 2015