A fever in children is a rectal temperature of 100.4°F (38.0°C) or higher. It’s one of the most common reasons parents call their pediatrician, and in most cases, it’s a sign that a child’s immune system is actively fighting off an infection rather than a sign of something dangerous. Fevers below 104°F associated with common viral infections like the flu can actually help the body fight disease and are generally not harmful.
That said, what counts as a fever, how you should measure it, and when to worry all depend on your child’s age. Here’s what you need to know.
Normal Temperature vs. Fever by Age
A healthy child’s body temperature typically falls between 97°F and 99°F, though it fluctuates throughout the day. It tends to be lowest in the morning and highest in the late afternoon. The universal threshold for fever is a rectal temperature of 100.4°F (38.0°C), but the number that matters most depends on how old your child is.
For babies under 3 months, any rectal temperature of 100.4°F or above is treated seriously. The American Academy of Pediatrics has specific guidelines for evaluating febrile infants aged 8 to 60 days, and even well-appearing babies in this age range need prompt medical evaluation. Their immune systems are still immature, and fever can be the only visible sign of a serious bacterial infection.
For older infants and toddlers, the temperature number matters less than how your child looks and acts. A child with a 103°F fever who is still drinking fluids, making eye contact, and playing between naps is generally in better shape than a child with a 101°F fever who is limp and unresponsive.
How to Take an Accurate Temperature
The thermometer you use and where you place it should match your child’s age. Armpit temperatures are the least accurate of all methods, so if an armpit reading concerns you, follow up with a more reliable measurement.
- Birth to 3 months: Use a standard digital thermometer rectally. Temporal artery (forehead) thermometers may also provide accurate readings in newborns. Pacifier thermometers and fever strips are not recommended.
- 3 months to 4 years: Rectal, armpit, or temporal artery thermometers all work. Digital ear thermometers are an option starting at 6 months. If you’re unsure about a non-rectal reading, a rectal temperature is the most reliable confirmation.
- 4 years and older: Most children can hold a digital thermometer under their tongue long enough for an oral reading. Ear and forehead thermometers are also fine at this age.
Keep in mind that armpit readings run about 1°F lower than rectal readings, and oral readings fall somewhere in between. If you’re comparing numbers over time, try to use the same method and the same thermometer each time.
Why Children Get Fevers
Fever is not an illness. It’s a defense mechanism. When your child’s immune system detects a virus or bacteria, the brain raises the body’s thermostat. The higher temperature makes it harder for many pathogens to replicate and helps immune cells work more efficiently.
The vast majority of childhood fevers are caused by common viral infections: colds, flu, stomach bugs, roseola, hand-foot-and-mouth disease. These fevers typically last three to five days and resolve on their own. Bacterial infections like ear infections, strep throat, or urinary tract infections can also cause fever, and these usually need treatment with antibiotics. Less commonly, fever can follow vaccinations, which is a normal immune response that typically lasts one to two days.
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. If your child has a mild fever but is eating, drinking, and behaving mostly normally, medication isn’t always necessary.
When your child is clearly uncomfortable, acetaminophen and ibuprofen are the two standard options. Both are dosed by weight, not age, so check the packaging carefully. Acetaminophen can be given every 4 to 6 hours, with no more than 5 doses in 24 hours. Ibuprofen can be given every 6 to 8 hours, with no more than 4 doses in 24 hours. One important distinction: ibuprofen is not recommended for babies under 6 months old.
Never give aspirin to a child or teenager. It’s linked to a rare but serious condition called Reye’s syndrome that affects the brain and liver.
Keeping Your Child Hydrated
Fever increases fluid loss through sweat and faster breathing, so dehydration is the most common complication to watch for. Offer small, frequent sips of water, breast milk, formula, or an oral rehydration solution throughout the day. Popsicles and diluted juice work for older kids who refuse plain water.
Watch for these signs of dehydration: a dry mouth or cracked lips, no tears when crying, no wet diapers for three hours or more, sunken eyes or a sunken soft spot on a baby’s head, skin that doesn’t flatten back quickly after being gently pinched, and unusual crankiness or low energy. If you notice several of these together, your child needs fluids and possibly medical attention.
Febrile Seizures
Febrile seizures affect about 2% to 5% of children between the ages of 6 months and 5 years. They’re triggered by a rapid rise in body temperature, not by how high the fever gets, which means they can happen before you even realize your child has a fever.
During a febrile seizure, a child may stiffen, shake uncontrollably, or lose consciousness. Most episodes last less than five minutes and stop on their own. If your child has one, lay them on their side on a flat surface, don’t put anything in their mouth, and time the seizure. While terrifying to witness, simple febrile seizures do not cause brain damage or epilepsy. A seizure lasting longer than five minutes, or one that affects only one side of the body, needs emergency evaluation.
Signs That Need Immediate Attention
Most fevers are harmless, but certain warning signs alongside a fever signal something more serious. Seek medical care right away if your child shows any of the following:
- Any fever in a baby under 3 months: A rectal temperature of 100.4°F or higher at this age always warrants a call or visit, even if the baby looks fine.
- Extreme sleepiness or unresponsiveness: If your child is unusually difficult to wake, or not responding to your voice or touch, that’s a red flag.
- Breathing problems: Fast, labored, or shallow breathing, chest retracting with each breath, or blue-tinged lips or face all require immediate help. Call 911 if you see blue coloring.
- Rash that doesn’t fade when pressed: A flat rash or purple spots that stay visible when you press a glass against them could indicate a serious bacterial infection like meningitis.
- Stiff neck: If your child resists moving their neck or can’t bend it forward, this is another possible sign of meningitis.
- Inconsolable crying: A high-pitched, unusual cry that can’t be soothed may signal pain or distress beyond normal fussiness.
- A bulging soft spot: In babies, a soft spot that pushes outward can mean increased pressure inside the skull.
- Fever lasting more than five days: Even a low-grade fever that persists beyond five days can indicate an underlying issue that needs investigation.
The most reliable gauge of severity is your child’s behavior between fever spikes. Children who perk up when their temperature drops, make eye contact, take fluids willingly, and can be comforted are generally fighting a routine infection. Children who remain listless, refuse all fluids, or look “off” to you even when their fever is down deserve a closer look. You know your child’s baseline better than any thermometer reading can capture.