A fever in children is a temperature of 100.4°F (38°C) or higher when measured rectally, in the ear, or on the forehead. Oral readings count as a fever at 100°F (37.8°C), and armpit readings at 99°F (37.2°C). The number that qualifies as a fever depends on where you take the temperature, because different parts of the body run slightly warmer or cooler than others.
Fever Thresholds by Measurement Method
Not all thermometers give the same reading, and knowing which number matters for each method saves a lot of confusion. Here are the cutoffs:
- 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
Armpit temperatures are the least accurate of these options. If you get a borderline armpit reading and your child seems unwell, take the temperature again using a different method. Ear thermometers can also be thrown off by earwax or a small, curved ear canal, which is common in younger children. For babies under 3 months, a rectal reading gives the most reliable result.
Why Children Get Fevers
A fever is not an illness. It’s the body’s response to fighting off an infection, almost always caused by a virus like a cold, flu, or stomach bug. Bacterial infections, ear infections, and urinary tract infections can also trigger fevers. The immune system raises the body’s temperature on purpose because many germs reproduce less effectively in warmer conditions.
One common source of confusion is teething. Teething does not cause a true fever. It can push a baby’s temperature slightly above normal, but it stays below the 100.4°F threshold. If your teething baby has a temperature at or above 100.4°F, something else is going on.
How Long a Fever Typically Lasts
Most fevers follow the natural course of the infection causing them, which is typically one to four days. A fever that hangs around for more than four days without a clear explanation warrants a call to your child’s pediatrician. That doesn’t necessarily mean something serious is happening, but it’s worth investigating the cause rather than waiting it out further.
When a Fever Needs Immediate Attention
The number on the thermometer matters less than how your child looks and acts. A child with a temperature of 102°F who is playing and drinking fluids is generally in better shape than a child at 100.5°F who is limp and unresponsive. That said, certain situations call for urgent medical care regardless of how your child appears.
Babies Under 3 Months
Any fever of 100.4°F or higher in a baby younger than 3 months requires a call to the doctor right away. Young infants don’t have fully developed immune systems, and a fever at this age can signal a serious infection that needs rapid evaluation. Don’t give fever-reducing medication and wait to see what happens. Call first.
Warning Signs at Any Age
Take your child to an emergency department or call emergency services if they have a fever along with any of these symptoms:
- Difficulty breathing or rapid, labored breaths
- Extreme drowsiness where your child is hard to wake up or seems confused
- Pale, blotchy, or blue-tinged skin, especially around the lips
- A rash that doesn’t fade when you press on it (roll a glass over it to check)
- A stiff or sore neck combined with vomiting, headache, or sensitivity to bright light, which can indicate meningitis
- A seizure
- Signs of dehydration: refusing to drink, no wet diapers for several hours, or repeated vomiting
In very young babies, also watch for nonstop crying that nothing soothes, or a bulging soft spot on the top of the head.
Febrile Seizures
Some children have seizures triggered by a fever, called febrile seizures. These are most common between 6 months and 5 years old, with the peak risk between ages 1 and 3. During a febrile seizure, a child may stiffen, shake, or briefly lose consciousness. It typically lasts less than a few minutes.
As frightening as febrile seizures look, most are not harmful and don’t cause lasting effects. They tend to happen as a fever spikes rapidly, not necessarily when it’s at its highest point. You can’t prevent them by giving fever reducers early. If your child has a seizure, lay them on their side on a safe surface, don’t put anything in their mouth, and time how long it lasts. Call your doctor afterward, or call emergency services if the seizure lasts more than five minutes.
Treating a Fever at Home
A fever doesn’t always need to be treated. If your child is comfortable, drinking well, and still somewhat active, you can let the fever do its job. Treatment is really about comfort, not about getting the number on the thermometer back to normal.
When your child is miserable, acetaminophen and ibuprofen are the two main options. Acetaminophen can be given every 4 hours for children under 12, with no more than 5 doses in 24 hours. Ibuprofen should not be given to babies under 6 months old. For both medications, dose by your child’s weight rather than age for the most accurate amount. The product packaging includes weight-based dosing tables, and your pharmacist or pediatrician can help if you’re unsure.
Never give aspirin to children or teenagers. It’s linked to a rare but serious condition that affects the liver and brain.
Comfort Measures That Help
Dress your child in light clothing rather than bundling them up. Heavy blankets and layers trap heat and can push the temperature higher. Offer fluids frequently, even if your child only takes small sips at a time. Water, diluted juice, ice pops, and broth all count. The goal is to prevent dehydration, which is the real risk with most childhood fevers.
A lukewarm (not cold) bath can help a child feel better temporarily. Avoid rubbing alcohol baths, which are an old remedy that can be dangerous because the alcohol absorbs through the skin. A cool washcloth on the forehead offers comfort but won’t significantly lower body temperature.
What the Number Actually Tells You
Parents often focus on how high the fever gets, but the temperature alone doesn’t reliably predict how serious the illness is. A child with a 104°F fever from a common virus can recover in a day or two, while a child with a lower fever from a bacterial infection might need treatment. What matters more is the overall picture: how your child is behaving, whether they’re keeping fluids down, how long the fever has lasted, and whether other concerning symptoms are present. The thermometer gives you one data point. Your child’s behavior gives you the rest.