Febrile Illness with Uncertain Cause (Child)

Your child has a fever, but the cause is not certain. A fever is a natural reaction of the body to an illness, such as infections due to a virus or bacteria. In most cases, the temperature itself is not harmful. It actually helps the body fight infections. A fever does not need to be treated unless your child is uncomfortable and looks and acts sick.

Home care

  • Keep clothing to a minimum because excess body heat needs to be lost through the skin. The fever will increase if you dress your child in extra layers or wrap your child in blankets.

  • Fever increases water loss from the body. For infants under 1 year old, continue regular feedings (formula or breastmilk). Between feedings, give oral rehydration solution. This is available from grocery stores and drugstores without a prescription. For children 1 year or older, give plenty of fluids, such as water, juice, soft drinks such as ginger ale or lemonade, or ice pops. 

  • If your child doesn’t want to eat solid foods, it’s OK for a few days, as long as he or she drinks lots of fluids.

  • Keep children with fever at home resting or playing quietly. Encourage frequent naps. Your child may return to daycare or school when the fever is gone and he or she is eating well and feeling better.

  • Periods of sleeplessness and irritability are common. If your child is congested, try having him or her sleep with the head and upper body raised up. You can also raise the head of the bed frame by 6 inches on blocks. 

  • Monitor how your child is acting and feeling. If he or she is active and alert, and is eating and drinking, there is no need to give fever medicine.

  • If your child becomes less and less active and looks and acts sick, and his or her temperature is 100.4ºF (38ºC) or higher, you may give acetaminophen. In infants 6 months or older, you may use ibuprofen instead of acetaminophen. Follow instructions from your child’s healthcare provider on how to dose these medicines. Talk with the health care provider before using these medicines if your child has chronic liver or kidney disease. Also talk with the provide if your child has ever had a stomach ulcer or digestive bleeding. Never give aspirin to anyone under age 19. It can put your child at risk for Reye syndrome. This is a rare but serious disorder that most often affects the brain and the liver. 

  • Don't wake your child to give fever medicine. Your child needs sleep to get better.

Follow-up care

Follow up with your child's healthcare provider, or as advised, if your child isn't better after 2 days. If blood or urine tests were done, call as advised for the results.

When to get medical advice

Unless your child's healthcare provider advises otherwise, call the provider right away if any of these occur: 

  • Fever (see "Fever and children" below)

  • Your baby is fussy or cries and can't be soothed.

  • Your child is breathing fast, as follows:

    • Birth to 6 weeks: more than 60 breaths per minute (breaths/minute)

    • 6 weeks to 2 years: over 45 breaths/minute

    • 3 to 6 years: over 35 breaths/minute

    • 7 to 10 years: over 30 breaths/minute

    • Older than 10 years: over 25 breaths/minute

  • Your child is wheezing or has trouble breathing.

  • Your child has an earache, sinus pain, stiff or painful neck, or headache.

  • Your child has belly pain or pain that is not getting better after 8 hours.

  • Your child has repeated diarrhea or vomiting.

  • Your child shows unusual fussiness, drowsiness or confusion, weakness, or dizziness

  • Your child has a rash or purple spots.

  • Your child shows signs of dehydration, including:

    • No tears when crying

    • Sunken eyes or dry mouth

    • No wet diapers for 8 hours in infants

    • Reduced urine output in older children

  • Your child feels a burning sensation when urinating

  • Your child has a convulsion (seizure)

Fever and children

Use a digital thermometer to check your child’s temperature. Don’t use a mercury thermometer. There are different kinds and uses of digital thermometers. They include:

  • Rectal. For children younger than 3 years, a rectal temperature is the most accurate.

  • Forehead (temporal). This works for children age 3 months and older. If a child under 3 months old has signs of illness, this can be used for a first pass. The provider may want to confirm with a rectal temperature.

  • Ear (tympanic). Ear temperatures are accurate after 6 months of age, but not before.

  • Armpit (axillary). This is the least reliable but may be used for a first pass to check a child of any age with signs of illness. The provider may want to confirm with a rectal temperature.

  • Mouth (oral). Don’t use a thermometer in your child’s mouth until he or she is at least 4 years old.

Use the rectal thermometer with care. Follow the product maker’s directions for correct use. Insert it gently. Label it and make sure it’s not used in the mouth. It may pass on germs from the stool. If you don’t feel OK using a rectal thermometer, ask the healthcare provider what type to use instead. When you talk with any healthcare provider about your child’s fever, tell him or her which type you used.

Below are guidelines to know if your young child has a fever. Your child’s healthcare provider may give you different numbers for your child. Follow your provider’s specific instructions.

Fever readings for a baby under 3 months old:

  • First, ask your child’s healthcare provider how you should take the temperature.

  • Rectal or forehead: 100.4°F (38°C) or higher

  • Armpit: 99°F (37.2°C) or higher

Fever readings for a child age 3 months to 36 months (3 years):

  • Rectal, forehead, or ear: 102°F (38.9°C) or higher

  • Armpit: 101°F (38.3°C) or higher

Call the healthcare provider in these cases:

  • Repeated temperature of 104°F (40°C) or higher in a child of any age

  • Fever of 100.4°F (38°C) or higher in baby younger than 3 months

  • Fever that lasts more than 24 hours in a child under age 2

  • Fever that lasts for 3 days in a child age 2 or older

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