A fever is a higher-than-normal body temperature. Fever of unknown origin is diagnosed when a child has a fever for longer than a week and testing doesn't find the cause.

At this time, a specific cause for your child's fever wasn't found. Your child's healthcare provider will continue to work with you to find out what is causing your child's fever.

It's important to know how to check your child's temperature and what to do if your child gets any new or worsening symptoms.

• Follow your healthcare provider's instructions for:
  • When to take your child's temperature
  • If your child needs more testing or needs to see any medical specialists
  • When to follow up
• Give your child any medicines as instructed by your healthcare provider.
• If your child feels warm, take their temperature. The best way to take their temperature will depend on your child's age and how well they can cooperate:
  • For babies younger than 3 months old, a rectal thermometer (in the bottom) is best.
  • For babies 3–6 months old, a rectal thermometer is best, but you can also use a temporal artery (across the forehead) or axillary (under the armpit) thermometer.
  • For kids 6 months to 3 years old, a rectal thermometer is best, but you can also use a temporal artery, axillary, or tympanic (in the ear) thermometer.
  • For kids who are old enough to hold the thermometer in their mouth (typically by about 4–5 years old), it's best to use an oral (under the tongue) thermometer. You can also use a temporal artery, axillary, or tympanic thermometer.
• Use this table to see if your child has a fever:

• Keep a record (on paper or on your phone) of your child's fever, including:
  • The temperature and how it was taken (such as in the bottom, under the tongue, or the armpit)
  • The date and time you took the temperature
  • Any other symptoms your child had at the time (such as a cough, runny nose, headache, or belly pain)
  • Any medicines you gave your child
• Do not use a glass thermometer. They are not safe.
• If your child is uncomfortable from the fever, and your healthcare provider says it's OK, you can give acetaminophen (Tylenol® or a store brand) or ibuprofen (Advil®, Motrin®, or a store brand). Follow the directions on the label for how much to give and how often. Don't give ibuprofen to babies under 6 months old.
• Don't give aspirin to your child. It can cause a rare but serious illness called Reye syndrome.
• Offer your child plenty of fluids to drink.
• Let your child rest as needed.
• Your child may return to childcare or school after the fever has been gone for 24 hours without medicine that lowers fever (such as acetaminophen or ibuprofen).

Your child:

• Is drinking very little
• Gets a new fever after the fever went away, still has a fever after 2–3 days, or has a higher fever
• Develops new or worsening symptoms, such as vomiting (throwing up); diarrhea; cough or congestion; a rash; bad-smelling pee or pain when peeing; belly, ear, or joint pain; or a sore throat
• Seems to be getting sicker

Your child:

• Isn't drinking at all or has signs of dehydration (not enough water in the body), such as a dry or sticky mouth, sunken eyes, less pee or darker pee than usual, little or no tears when crying, or unusual sleepiness
• Is very upset or is crying nonstop and can't be calmed down
• Develops a severe headache, a stiff neck, a rash, bruising, or red dots on the skin, fast breathing, or trouble swallowing (These can all be signs of a serious infection.)
• Has a seizure (uncontrolled body movements)

You know your child best. If they have symptoms that worry you or seem very sick, call your healthcare provider or take your child to the ER.

What causes fever of unknown origin? In kids, viruses or bacteria (types of germs) usually cause fever of unknown origin. Less often, it can be a sign of inflammation (pain and swelling) in the body or a reaction to a medicine.

If my child feels warm, is it always fever? Not all kids who feel warm have a fever, so it's best to take their temperature if you have any concerns. Kids can feel warm when they are very active, play outdoors in hot weather, sleep in warm pajamas under blankets, or are upset and crying. These things make the skin feel hot because the skin is doing its job of getting rid of heat in the body.

Do all fevers need treatment? No. If your child has a fever but seems well, is alert, is drinking, and is acting normally, there's no need to give medicine to lower the fever. If your child seems cranky, tired, and uncomfortable, lowering the fever with medicine (such as acetaminophen or ibuprofen) can help your child feel better.