Written by the doctors and editors at UpToDate
What is a fever? — A fever is a rise in body temperature that goes above a certain level.
In general, a fever means a temperature above 100.4ºF (38ºC). You might get slightly different numbers depending on how you take your child’s temperature – oral (mouth), armpit, ear, forehead, or rectal.
Armpit, ear, and forehead temperatures are easier to measure than rectal or oral temperatures, but they are not as accurate. Even so, the height of the temperature is less important than how sick your child seems to you. If you think your child has a fever, and he or she seems sick, your child’s doctor or nurse might want you to double-check the temperature with an oral or rectal reading.
What is the best way to take my child’s temperature? — The most accurate way is to take a rectal temperature (figure 1).
Oral temperatures are also reliable when done in children who are least 4 years old. Here is the right way to take a temperature by mouth:
- Wait at least 30 minutes after your child has drunk or eaten anything hot or cold.
- Wash the thermometer with cool water and soap. Then rinse it.
- Place the tip of the thermometer under your child’s tongue toward the back. Ask your child to hold the thermometer with his or her lips, not teeth.
- Have your child keep his or her lips sealed around the thermometer. A glass thermometer takes about 3 minutes to work. Most digital thermometers take less than 1 minute.
Armpit, ear (figure 2), and forehead temperatures are not as accurate as rectal or oral temperatures.
What causes fever? — The most common cause of fever in children is infection. For example, children can get a fever if they have:
- A cold or the flu
- An airway infection, such as croup or bronchiolitis
- A stomach bug
In some cases, children get a fever after getting a vaccine.
Should I take my child to see a doctor or nurse? — You should take your child to a doctor or nurse if he or she is:
- Younger than 3 months and has a rectal temperature of 100.4ºF (38ºC) or higher. Your infant should see a doctor or nurse even if he or she looks normal or seems fine. Do not give fever medicines to an infant younger than 3 months unless a doctor or nurse tells you to.
- Between 3 and 36 months and has a rectal temperature of 100.4ºF (38ºC) or higher for more than 3 days. Go right away if your child seems sick or is fussy, clingy, or refuses to drink fluids.
- Between 3 and 36 months old and has a rectal temperature of 102ºF (38.9ºC) or higher.
Children of any age should also see a doctor or nurse if they have:
- Oral, rectal, ear, or forehead temperature of 104ºF (40ºC) or higher
- Armpit temperature of 103ºF (39.4ºC) or higher
- A seizure caused by a fever
- Fevers that keep coming back (even if they last only a few hours)
- A fever as well as an ongoing medical problem, such as heart disease, cancer, lupus, or sickle cell anemia
- A fever as well as a new skin rash
What can I do to help my child feel better? — You can:
- Offer your child lots of fluids to drink. Call the doctor or nurse if your child won’t or can’t drink fluids for more than a few hours.
- Encourage your child to rest as much as he or she wants. But don’t force your child to sleep or rest. (Your child can go back to school or regular activities after he or she has had a normal temperature for 24 hours.)
Some parents give their children sponge baths to cool them down, but that is not usually necessary. Sometimes people think they can cool a child down by putting rubbing alcohol on their skin or adding it to a bath. But this is dangerous. Do not use any kind of alcohol to try to treat a fever.
How are fevers treated? — That depends on what is causing the fever. Many children do not need treatment. Those who do might need:
- Antibiotics to fight the infection causing the fever. But antibiotics work only on infections caused by bacteria, not on infections caused by viruses. For example, antibiotics will not work on a cold.
- Medicines, such as acetaminophen (sample brand name: Tylenol) or ibuprofen (sample brand names: Advil, Motrin) can help bring down a fever. But these medicines are not always necessary. For instance, a child older than 3 months who has a temperature of less than 102ºF (38.9ºC), and who is otherwise healthy and acting normally, does not need treatment
If you do not know how best to handle your child’s fever, call his or her nurse or doctor.
Never give aspirin to a child younger than 18 years old. Aspirin can cause a dangerous condition called Reye syndrome.
All topics are updated as new evidence becomes available and our peer review process is complete.
figure 1: Measuring rectal temperature
Lay your child face down across your lap. Put a dab of petroleum jelly (sample brand name: Vaseline) on the end of the thermometer.Then gently insert the thermometer into the child’s anus until the silver tip is not visible (1/4 to 1/2 inch [6 to 12 millimeters] inside the anus). Hold the thermometer in place. A glass thermometer takes about 2 minutes. Most digital thermometers need less than 1 minute.
figure 2: Measuring ear temperature
To take an ear temperature, make sure you are using a thermometer meant for this. Pull your child’s ear back before inserting the thermometer. Then hold the tip in your child’s ear for about 2 seconds.