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 F (36.1 C) and 99 F (37.2 C) 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 have.

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.
• Use a light blanket if your child feels chilled, until the chills end.
• Don't give aspirin to children or teenagers.
• Don't give an infant any type of pain reliever until after you've contacted a doctor and your child has been evaluated.
• 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.

When to seek medical advice for a child

If your baby is less than 3 months old and has a fever, it's important to get medical help immediately.

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

• Fussiness, or acting abnormally, which doesn't improve even after taking medications to bring down the fever
• Signs and symptoms of dehydration, such as no wet diapers over eight to 10 hours, crying without tears, a dry mouth or refusing to drink any fluids
• Stiff neck or a headache
• Abdominal pain
• Trouble breathing
• Rash
• Joint pain or swelling

Also get medical help if the fever lasts more than five days in a row.

Treating fever in an adult

Adults with fevers of 103 F (39.4 C) or higher will generally look and act sick. The main goal of treatment is to relieve discomfort and help you get rest.

To treat a fever at home:

• Drink plenty of fluids to stay hydrated.
• Dress in lightweight 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.

When to seek medical advice for an adult

Seek medical care if someone with a fever has any of the following signs and symptoms:

• Difficulty breathing
• Chest pain
• Severe headache
• Confusion or agitation
• Abdominal pain
• Repeated vomiting
• Dry mouth, decreased or dark urine, or refusal to drink fluids, which may indicate dehydration
• Skin rashes
• Difficulty swallowing fluids
• Pain with urination or pain in the back

When to seek emergency care

Seek emergency medical care if your child has a fever after being left in a hot car or involved in another 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

How to take a temperature

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

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

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 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 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 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 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.

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 indicating it's done.
• Remove the thermometer and read the number.

Ear temperature

• Turn on the digital thermometer. Gently place it in the ear canal 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.