A fever in a child is a rectal, ear, or forehead temperature of 100.4°F (38°C) or higher. For an oral reading, the threshold is 100°F (37.8°C), and for an armpit measurement, it’s 99°F (37.2°C). These numbers matter because the method you use to take your child’s temperature changes what counts as a fever.
Fever itself isn’t a disease. It’s the body’s deliberate response to infection, and in most cases it’s a sign that your child’s immune system is doing its job. Understanding when a fever is routine and when it signals something serious can save you a lot of unnecessary worry, while also helping you recognize the moments that genuinely need medical attention.
Why the Body Produces a Fever
When your child’s immune system detects an invader like a virus or bacteria, it raises the body’s internal thermostat. This isn’t a malfunction. Research from the National Institutes of Health has shown that immune cells become significantly more active at fever temperatures. At around 102.2°F, certain white blood cells multiply faster, release more infection-fighting signals, and mount a stronger inflammatory response than they do at normal body temperature. At the same time, the cells that normally dial down immune activity become less effective, letting the body go on the offensive.
In practical terms, a mild to moderate fever is your child’s immune system turning up the heat to create an environment that’s harder for germs to thrive in and easier for the body to fight back. That’s why treating a fever isn’t always necessary. The goal is to keep your child comfortable, not to eliminate the fever entirely.
What Causes Fevers in Children
The vast majority of childhood fevers are caused by viral infections. Upper respiratory infections (the common cold), flu, ear infections, roseola, tonsillitis, and common childhood illnesses like chickenpox are all frequent culprits. Urinary tract infections and kidney infections can also cause fever, sometimes without obvious symptoms in younger children.
Less commonly, fever signals a serious bacterial illness such as pneumonia, a bloodstream infection, or meningitis. These conditions are rare but important to recognize because they require prompt treatment. Teething, while often blamed for fevers, typically causes only a very slight rise in temperature, not a true fever above 100.4°F.
How to Take an Accurate Temperature
The method you use depends on your child’s age. For babies and toddlers under 3, a rectal thermometer gives the most accurate reading. Place the tip about half an inch into the rectum and wait for the beep. For children 4 and older, an oral thermometer under the tongue works well. Armpit readings are the least accurate but can be useful as a quick screen.
Ear and forehead thermometers are convenient and reasonably accurate for children over 6 months, though earwax or improper positioning can sometimes throw off the reading. If you get a number that seems off, take it again. The specific thresholds to remember:
- Rectal, ear, or forehead: 100.4°F (38°C) or higher
- Oral: 100°F (37.8°C) or higher
- Armpit: 99°F (37.2°C) or higher
Fever in Babies Under 3 Months
This is the one age group where fever demands immediate medical evaluation, regardless of how well the baby seems. Any rectal temperature of 100.4°F or higher in an infant 90 days old or younger is treated seriously. The American Academy of Pediatrics has specific guidelines broken into age brackets (8 to 21 days, 22 to 28 days, and 29 to 60 days) because the younger the baby, the higher the risk that a fever represents a dangerous bacterial infection.
Newborns don’t always look sick even when they are. Their immune systems are immature, and infections can progress quickly. For babies in the first month of life, a fever typically means blood tests, urine tests, and sometimes a spinal fluid test to rule out meningitis, along with a hospital stay of at least 36 hours while cultures are monitored. For babies in the second and third month, the workup is similar but may be less intensive depending on risk factors and test results.
Abnormally low temperature (below 96.8°F) in a young infant is also a warning sign. It can indicate infection just as a fever does.
Keeping Your Child Comfortable at Home
For children older than 3 months with a mild to moderate fever, home care is often all that’s needed. The priority is comfort, not hitting a specific number on the thermometer.
Dress your child in light, comfortable clothing. Bundling them in extra layers or blankets can actually trap heat and push the temperature higher. A single layer of pajamas in a comfortably cool room is usually right. Lukewarm sponge baths can help some children feel better, but avoid cold water or ice baths, which cause shivering and can raise core temperature.
Fluids are essential. Fever increases fluid loss through sweating and faster breathing, making dehydration a real concern. Offer water, diluted juice, or an oral rehydration solution frequently. For breastfed babies, nurse more often than usual. Watch for signs that your child isn’t getting enough fluids: no wet diapers for three hours, a dry mouth, no tears when crying, sunken eyes, or skin that stays pinched up instead of flattening back immediately. These signs mean your child needs medical attention for dehydration.
Fever-Reducing Medication
Children’s acetaminophen (Tylenol) can be given every 4 to 6 hours, up to 5 times in 24 hours. It should not be given to infants under 8 weeks old. Children’s ibuprofen (Advil, Motrin) can be given every 6 to 8 hours, up to 4 times in 24 hours, but only to children 6 months and older.
Always dose by your child’s weight, not their age. The weight-based dosing chart on the package or from your pediatrician is far more accurate than going by age alone. Never give aspirin to children or teenagers, as it’s linked to a rare but serious condition called Reye’s syndrome.
You don’t have to give medication every time your child has a fever. If they’re playing, drinking, and reasonably comfortable at 101°F, it’s fine to let the fever do its work. Medication is most helpful when the fever is making your child miserable, disrupting sleep, or climbing high enough to cause real discomfort.
Febrile Seizures
Up to 5% of young children will experience a febrile seizure at some point, most commonly between 14 and 18 months of age. These seizures can happen in children between 6 months and 5 years old and are triggered by the rapid rise in temperature rather than by how high the fever gets. A child can seize at 101°F if the temperature spiked quickly.
Febrile seizures are terrifying to witness but are almost always harmless. They typically last less than a few minutes, and children recover fully. During a seizure, lay your child on their side on a safe surface, don’t put anything in their mouth, and time the episode. If it lasts longer than 5 minutes or your child doesn’t return to normal afterward, call emergency services. A first febrile seizure warrants a call to your pediatrician even if it resolves quickly, so they can rule out other causes.
Giving fever-reducing medication proactively does not prevent febrile seizures. Because the seizure is triggered by the speed of the temperature change, medication given after the fever has already started rising can’t reliably stop one from happening.
Warning Signs That Need Immediate Attention
Most fevers resolve on their own within a few days. But certain symptoms alongside a fever indicate something more serious is happening. Seek emergency care if your child has any of the following:
- Altered consciousness or floppiness: your child seems unusually limp, difficult to wake, or unresponsive
- A stiff neck: especially combined with light sensitivity or headache, which can point to meningitis
- A non-blanching rash: tiny red or purple spots that don’t fade when you press a glass against the skin, which can signal a blood infection
- A bulging soft spot: on the top of a baby’s head
- Mottled, bluish, or very pale skin
- A weak, high-pitched, or continuous cry that sounds different from your child’s usual cry
- Severe limb or joint pain
- Fever lasting more than 5 days: especially with a rash, red eyes, swollen hands or feet, or a “strawberry tongue,” which are signs of Kawasaki disease
Also trust your instincts. Parents often notice subtle changes in their child’s behavior before measurable symptoms appear. If your child looks or acts sicker than you’ve seen before during a typical illness, that observation is worth acting on, even if you can’t point to a specific symptom from a list.