A fever in a child is a rectal temperature of 100.4°F (38.0°C) or higher. In most cases, it means your child’s immune system is doing its job, and your main task is keeping them comfortable and hydrated while their body fights off the infection. But age matters enormously: a fever in a baby under 3 months old is always a reason to call your pediatrician or head to the emergency room, even if your baby looks fine.
What Counts as a Fever
The standard threshold is 100.4°F (38.0°C) measured rectally. Rectal thermometers are the most accurate option for children under 3, and pediatric guidelines worldwide use this as the benchmark. Oral and underarm readings run lower than rectal ones. An oral reading tends to be about 0.7°F lower, and an underarm reading about 1.3°F lower. So if your child’s underarm temperature is 99.1°F, that roughly corresponds to 100.4°F rectally.
For older children who can hold a thermometer under their tongue, oral readings above 99.5°F (37.5°C) are considered above normal range. If you’re ever unsure whether the number you’re seeing qualifies as a fever, a rectal check gives you the clearest answer.
Why Fever Is Not the Enemy
Fever is one of the body’s most effective weapons against infection. At temperatures in the febrile range (around 104°F), the replication rate of certain viruses drops by more than 200-fold, and bacteria become more vulnerable to destruction by the immune system. Febrile temperatures boost nearly every step of the immune response, both the fast-acting frontline defenses and the slower, targeted response that builds lasting immunity.
This is why pediatricians generally recommend treating your child’s discomfort rather than chasing a specific number on the thermometer. A child with a 102°F fever who is playing and drinking fluids may not need medication at all, while a child at 100.5°F who is miserable and refusing to drink probably does.
Babies Under 3 Months: Act Immediately
Any rectal temperature of 100.4°F or above in a baby 90 days old or younger requires prompt medical evaluation, even if the baby seems well. The reason is straightforward: at this age, a fever can be the only visible sign of a serious bacterial infection, including bloodstream infections or meningitis. About 1.6% of febrile infants in this age group have bacteria in the blood, and 0.4% have bacterial meningitis. Those numbers are small, but the stakes are high enough that doctors will want to run blood work, a urine test, and possibly additional testing to rule out dangerous causes.
Do not give fever-reducing medication to a baby this young without guidance from a doctor. Head to the emergency room or call your pediatrician right away.
Fever-Reducing Medication
Two over-the-counter options are safe for children: acetaminophen (Tylenol) and ibuprofen (Advil, Motrin). The most important rule for both is to dose by your child’s weight, not their age.
Acetaminophen can be given to children of all ages, including newborns when directed by a doctor. The liquid form comes as 160 mg per 5 mL. You can give a dose every 4 hours if symptoms persist, but no more than 5 doses in 24 hours.
Ibuprofen is not approved for babies under 6 months. For children 6 months and older, it can be given every 6 to 8 hours. Ibuprofen has the added benefit of reducing inflammation, which can help with ear infections or sore throats. Never give aspirin to a child or teenager, as it’s linked to a rare but serious condition called Reye’s syndrome, especially during viral illnesses.
If you’re unsure about the right dose for your child’s weight, your pharmacist can help. The dosing charts on the packaging are reliable when you use your child’s current weight.
Keeping Your Child Comfortable at Home
Hydration is the single most important thing you can manage at home. Fever increases fluid loss through sweating and faster breathing, and a sick child often has little appetite. For babies, continue breastfeeding or formula on demand. For older children, an oral rehydration solution is better than plain water or sports drinks because it replaces both fluids and electrolytes. Signs that your child is staying adequately hydrated include moist lips and mouth and eyes that look normal rather than sunken.
Dress your child in lightweight clothing and keep the room at a comfortable temperature. Bundling a feverish child in blankets can trap heat and push the temperature higher. A single light layer with a sheet is usually enough.
Should You Use a Cool Bath or Sponge Bath?
Sponging with cool water does bring a fever down quickly, often within 30 minutes. But the effect is short-lived. In one clinical comparison, 71% of sponged children returned to normal temperature by 30 minutes, but only 11% stayed there by the two-hour mark. Meanwhile, fever-reducing medication took longer to kick in but held steady. Sponging also caused significantly more discomfort: about a third of the children cried, and a quarter shivered.
If you do sponge your child, use lukewarm water rather than cold. Never use rubbing alcohol, which can be absorbed through the skin and is toxic. In most situations, medication alone is simpler, more effective over time, and less distressing for your child.
Red Flags That Need Emergency Care
Most childhood fevers resolve on their own within a few days and are caused by common viral infections. But certain symptoms alongside a fever signal something more serious. Get emergency help if your child has any of the following:
- Difficulty breathing. Fast, labored, or shallow breaths, chest pulling inward with each breath, or blue-tinged lips or face. Call 911 if you see these.
- Extreme lethargy or unresponsiveness. A sick child who is sleepy is normal. A child who is difficult to wake or doesn’t respond to you is not.
- A stiff neck. If your child resists bending their neck forward or cries when you try to move it, this could indicate meningitis.
- A rash that doesn’t fade when pressed, or purple spots on the skin. These can signal a serious bacterial infection in the bloodstream.
- A seizure lasting more than 5 minutes, or a seizure accompanied by vomiting, a stiff neck, or breathing problems.
Febrile Seizures
Seeing your child have a seizure during a fever is terrifying, but febrile seizures are more common than most parents realize and are almost always harmless. They occur in children between 6 months and 5 years old, with peak risk between 12 and 18 months. A typical febrile seizure lasts a few seconds to 15 minutes, involves shaking or stiffening on both sides of the body, and resolves on its own.
If it happens, lay your child on their side on a safe surface, don’t put anything in their mouth, and time the seizure. Call an ambulance if it lasts longer than 5 minutes. One important thing to know: giving fever medication does not prevent febrile seizures. These seizures are triggered by the rapid rise in temperature, not by how high the fever gets, and medication can’t outpace that initial spike.
When the Fever Should Be Rechecked
Beyond the emergency signs above, there are situations where a non-urgent call to your pediatrician makes sense. A fever lasting more than 3 days in a child of any age deserves a check-in, even if your child seems okay otherwise. The same goes for a fever that keeps returning after seeming to resolve, a child under 2 years with a fever lasting more than 24 hours with no obvious source like a runny nose or cough, or any time your instincts tell you something is off. You know your child’s baseline behavior better than anyone, and “they just don’t seem right” is a valid reason to seek a medical opinion.