A temperature of 100.4°F (38°C) or higher is considered a fever in children of any age. That single number is the standard threshold used by the American Academy of Pediatrics and most pediatric hospitals. But how urgently you need to act depends on your child’s age, how high the fever climbs, and what other symptoms are present.
The Key Number: 100.4°F
For children from newborns through teenagers, 100.4°F measured rectally is the medical definition of a fever. Temperatures below that, even in the 99 to 100°F range, are generally normal fluctuations. Body temperature rises naturally in the late afternoon and evening, so a reading of 99.5°F after a busy day of playing is not a fever.
Once a child crosses 100.4°F, the response depends largely on age:
- Under 3 months: Any fever of 100.4°F or higher needs an immediate call to your pediatrician, even if your baby seems fine otherwise. Newborns can’t fight infections the same way older children can, and a fever at this age sometimes signals a serious bacterial infection that needs rapid evaluation.
- 3 months to 2 years: A fever of 102°F or higher warrants a call to your pediatrician within 24 hours. Below 102°F, you can typically manage the fever at home as long as your child is drinking fluids and behaving relatively normally.
- 2 years and older: Fever alone is less concerning at this age. Focus more on how your child is acting than on the exact number on the thermometer.
- Any age, 105°F or higher: This is a medical emergency. Seek immediate care.
How Long a Fever Should Last
Short fevers that come and go over a day or two are common with viral infections and usually resolve on their own. The duration that should prompt a call to your pediatrician varies by age. For children under 2, contact your pediatrician if the fever lasts more than 24 hours. For children 2 and older, the threshold is 72 hours (three days). These timelines apply to fevers without other worrying symptoms. If your child looks or acts seriously ill at any point, don’t wait.
Where You Take the Temperature Matters
Not all thermometers give the same reading. Rectal temperatures are the most accurate for young children and are the standard pediatricians use when making clinical decisions. Other methods can read slightly higher or lower than the true core temperature.
Ear (tympanic) thermometers tend to read very close to a rectal thermometer, typically within a tenth of a degree. Forehead and temporal artery thermometers often read about half a degree Fahrenheit higher than actual core temperature, which means they may occasionally flag a fever that isn’t really there. Oral (under-the-tongue) thermometers tend to read slightly lower than rectal, roughly 0.3 to 0.5°F less.
For babies under 3 months, a rectal reading is the only one reliable enough to guide medical decisions. For older children, an ear or forehead thermometer is usually fine for home use, but if you get a borderline reading, a rectal or oral temperature gives a more trustworthy number.
What Febrile Seizures Look Like
Some children between 6 months and 5 years experience seizures triggered by fever, called febrile seizures. These typically happen when the temperature rises above 101°F, often during a rapid spike rather than at a sustained high temperature. Watching your child have a seizure is frightening, but febrile seizures are generally not harmful and don’t cause brain damage or epilepsy.
If it happens, gently lower your child to the floor and turn them on their side to prevent choking. Don’t try to hold them down, put anything in their mouth, or restrain their movements. Most febrile seizures last under two minutes and stop on their own. If a seizure lasts longer than five minutes, call 911.
Symptoms That Matter More Than the Number
A child with a 103°F fever who is still drinking, playing between rest periods, and making eye contact is generally in less danger than a child with a 101°F fever who is limp, unresponsive, or refusing all fluids. The temperature itself is your child’s immune system working. What matters most is how your child looks and acts.
Certain symptoms alongside a fever signal a true emergency regardless of the number on the thermometer:
- Lethargy: Your child stares into space, won’t smile, barely responds to you, or is too weak to cry.
- Dehydration: No urination for eight hours, no tears when crying, or a dry mouth and tongue.
- Breathing difficulty: Fast breathing, grunting, skin pulling in between the ribs, or bluish lips.
- Confusion: Sudden onset of saying strange things, not recognizing you, or seeing things that aren’t there.
- Purple or blood-red spots on the skin: Flat spots or dots that don’t fade when you press on them can indicate a serious bloodstream infection.
- Inconsolable crying: Constant, nonstop crying that nothing relieves, especially if your child can’t sleep or only sleeps briefly.
Managing a Fever at Home
The goal of treating a fever isn’t to eliminate it entirely. It’s to keep your child comfortable enough to rest and drink fluids. Two over-the-counter medications are commonly used: acetaminophen and ibuprofen. Both are dosed by weight, not age, so check your child’s current weight against the dosing chart on the package.
Acetaminophen can be given every 4 to 6 hours, up to five times in 24 hours. It’s available for all ages, including young infants (though always confirm with your pediatrician before giving any medication to a baby under 3 months). Ibuprofen can be given every 6 to 8 hours, up to four times in 24 hours, but only for children 6 months and older.
Beyond medication, dress your child in lightweight clothing, offer plenty of fluids, and keep the room at a comfortable temperature. Lukewarm baths can help but avoid cold water or ice baths, which can cause shivering and actually raise core temperature. Alcohol rubs are an old folk remedy that should never be used on children.