A fever is a rise in body temperature. It's often a sign of infection. Fever itself most often is harmless and it may play a role in fighting infection. Most fevers don't need treatment.

The average body temperature is 98.6 Fahrenheit (37 Celsius). But typical body temperature can range between 97 F (36.1 C) and 99 F (37.2 C) or more. Your body temperature can vary by how active you are, your age or the time of day. Most often, older people have lower body temperatures than younger people have.

These thermometer readings are thought to be a fever:

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

For a baby who's less than 3 months old and has a fever, get medical help right away.

Also, seek emergency medical care for a child who has any of these symptoms after being left in a hot car. These may be symptoms of a heat-related illness.

• Fever with no sweating or heavy sweating.
• Bad headache.
• Seizures.
• Stiff neck.
• Confusion.
• Repeated vomiting or diarrhea.
• Being irritable.
• Any symptoms that worry you.

The main goal of treatment is to improve comfort and help you or your child rest.

Infant and child

Children with fevers may not look or act sick. Treating a fever depends on how uncomfortable they are. If your child is uncomfortable or restless, these home care strategies may help:

• Have your child drink fluids.
• Dress your child in light clothing.
• Use a light blanket if your child feels chilled, until the chills end.
• If your child is 6 months old or older, give your child acetaminophen (Tylenol, others) or ibuprofen (Advil, Motrin, others). Read the label carefully for proper dosing. If your child has other health problems or takes medicine for them, check with your healthcare professional before using fever medicines.

Adult

Adults with fevers of 103 F (39.4 C) or higher will most often look and act sick. To treat a fever:

• Drink plenty of fluids.
• Dress in light clothing.
• Use a light blanket if you feel chilled, until the chills end.
• Take acetaminophen (Tylenol, others) or ibuprofen (Advil, Motrin IB, others). Follow the directions on the label. If you have other health problems or take medicine for them, check with your healthcare professional before using fever medicines.

• Don't give aspirin to children or teenagers.
• Don't give an infant any type of pain reliever until after you've talked with a healthcare professional.

Seek medical care if a child of any age shows any of the following:

• Fussiness or unusual behavior that doesn't improve even after taking medicine to bring down the fever.
• Symptoms of water loss, called dehydration. These include no wet diapers over 8 to 10 hours, crying without tears, a dry mouth or refusing to drink fluids.
• Stiff neck or a headache.
• Belly pain.
• Trouble breathing.
• Rash.
• Joint pain or swelling.
• Fever that lasts more than five days.

Seek medical care for an adult with a fever and any of the following:

• Trouble breathing.
• Chest pain.
• Bad headache or stiff neck.
• Being confused.
• Belly pain.
• Repeated vomiting.
• Symptoms of water loss, called dehydration. These include having a dry mouth, making less or dark urine, or not drinking fluids.
• Skin rashes.
• Trouble swallowing fluids.
• Pain with passing urine or pain in the back.

Fahrenheit-Celsius conversion table
Fahrenheit	Celsius
105	40.6
104	40.0
103	39.4
102	38.9
101	38.3
100	37.8
99	37.2
98	36.7
97	36.1
96	35.6

Always use a digital thermometer to check someone's temperature. Types you can get include:

• Rectal thermometers for use in the rectum.
• Oral thermometers for use in the mouth.
• Temporal artery thermometers. These use an infrared scanner to measure the temperature of the temporal artery in the forehead.
• Armpit, called axillary, and ear, called tympanic membrane thermometers. These are less accurate.

Because of the dangers of being exposed to mercury, don't use a glass mercury thermometer.

No matter which type of thermometer you use, do the following when using it:

• Read the instructions that came with the thermometer.
• Clean the thermometer 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 children alone while taking their 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 or side, with knees flexed.
• Carefully insert the tip 1/2 to 1 inch (1.3 to 2.5 centimeters) into the rectum.
• Hold the thermometer and the child still until the thermometer beeps, which means 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 as long as instructed or until the thermometer beeping shows it's done.
• Remove the thermometer and read the number.

Temporal artery temperature

• Turn on the digital thermometer. Gently sweep it across the forehead 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, which means it's done.
• Remove the thermometer and read the number.

Ear temperature

• Turn on the digital thermometer. Gently place it in the ear canal only as far as the instructions that came with the device say to.
• Hold the thermometer tightly in place until you hear the thermometer beep, which means it's done.
• Remove the thermometer and read the number.