Fever in Children
Quick Answer
Don’t judge the situation from the number alone. Check the measurement site, consider your child’s age, offer fluids, and pay attention to how your child looks and acts.
Your child feels hot. You check the thermometer, see a number, and suddenly you are trying to answer a much bigger question:
Is this a fever? Does the number matter? And what should I do next?
The good news is that you do not need to diagnose the cause of every fever at home. A better first step is to understand the temperature, your child’s age, how the temperature was measured, and how your child is acting.
What Is a Fever?
A fever is usually a sign that the body is responding to an illness or infection. Fevers are generally harmless and can be part of the body’s immune response.
But one important detail can easily get lost: a temperature threshold depends on how the temperature was measured.
According to the American Academy of Pediatrics (AAP), a rectal temperature of 100.4°F (38°C) or higher is ordinarily considered a fever. For oral, tympanic (ear), or temporal-artery readings, 100.4°F is generally used as the cutoff for a true fever. An axillary (armpit) reading may have a lower cutoff.
That means “100.4°F = fever” is incomplete without knowing the measurement site.
Does the Time of Day Affect Your Child’s Temperature?
The AAP notes that normal temperature can vary with age, activity, and time of day. Temperatures tend to be higher in the late afternoon and early evening and lower overnight, so the time you take your child’s temperature can be part of the context when you interpret the reading.
Two Things to Check Beyond the Number
Instead of focusing only on the thermometer, make two quick checks.
1. Check the age
Age matters because the same temperature does not carry the same significance for every child. For infants and young children, the AAP provides specific age-based guidance.
2. Check the child, not just the number
Is your child drinking? Are they interacting with you? Do they seem unusually sleepy, very fussy, or much sicker than usual?
A fever reading is one piece of the picture.
Fever Thresholds Are Age- and Context-Specific
This is the part parents most often want to simplify into one number. Unfortunately, the safe answer is more nuanced.
Babies 3 months or younger
For a baby 3 months or younger, the AAP says to call the pediatrician immediately for a rectal temperature of 100.4°F (38°C) or higher, even when there are no other signs of illness.
This is a specific recommendation for this young age group.
Babies 3 to 6 months
For a child 3 to 6 months old, the AAP’s HealthyChildren guidance indicates you may need to notify the doctor at 101°F (38.3°C).
This number should not be separated from its age group.
Children older than 6 months
The same AAP source indicates a child older than 6 months may need to have the doctor notified at 103°F (39.4°C).
That guidance comes from a source covering children from birth through age five. It should not be turned into a complete fever-threshold table for school-age children or teenagers.
What about 104°F?
The AAP also advises calling right away if the temperature rises above 104°F (40°C) repeatedly, at any age.
Notice that this is a different claim from the age-specific thresholds above.
FHG Science Note
Identical numbers can have different meanings when the population or purpose changes. A temperature used for infant medical guidance is not automatically the same as a temperature used for a school-attendance decision.
What Matters More Than Chasing the Number
The AAP recommends paying attention to your child’s overall condition.
It is a good sign if your child plays and interacts after receiving medicine for discomfort — but a lower temperature by itself does not mean the illness is no longer concerning.
Call your child’s doctor right away if your child:
- Looks very ill
- Is unusually drowsy
- Is extremely fussy
- Has a stiff neck
- Has a severe headache
- Has a severe sore throat
- Has severe ear pain
- Has difficulty breathing
- Develops an unexplained rash
- Has repeated vomiting or diarrhea
- Has had a seizure
- Has a condition or takes medicine that affects the immune system
- Has certain heart problems that make fever and an increased heart rate harder to tolerate
These signs matter because fever plus another concerning feature can be more important than the temperature by itself.
Watch the Direction, Not Just the Starting Point
A fever is not a snapshot. Your child’s condition can change.
The AAP advises contacting the pediatrician if:
- Your child still acts sick after the fever comes down.
- Your child seems to be getting worse.
- A fever lasts more than 24 hours in a child under 2 years.
- A fever lasts more than 3 days (72 hours) in a child 2 years or older.
Fever and Fluids
One of the simplest things you can do is encourage your child to drink enough fluids.
Keep your child drinking and watch for signs that they are becoming seriously ill. For what those signs look like at each age, see our guide to signs of dehydration in children.
If your child is repeatedly vomiting or having diarrhea along with a fever, this is one of the signs listed above that warrants calling your child’s doctor. Our guide to child vomiting and diarrhea covers what AAP guidance says about food, medicines and when to call.
If your child also has a cough, our guide to cough in children covers what AAP guidance says about home care and when to call.
If your child has ear pain along with the fever, our guide to ear pain in children covers what AAP guidance says about the signs that matter and when to call.
Common Myth
“My child is teething, so the fever must be from their teeth.”
Teething may cause a slight rise in body temperature within the normal range, but research shows teething does not cause a true fever. If a child seems particularly miserable or has a temperature higher than 100.3°F, it is probably not simply from teething and the pediatrician should be consulted.
Fever Is Not the Same Thing as Heatstroke
There is another important distinction.
A child who has been in a very hot environment, such as an overheated car, needs immediate attention. Heatstroke is related to extreme heat and dehydration rather than an ordinary infection. The body temperature can rise above 105°F (40.5°C) in heatstroke.
That number should not be added to the fever thresholds above. It belongs to a different safety situation.
If a child has been exposed to extreme heat and develops a very high body temperature, treat that as an urgent heat-related problem rather than assuming it is an ordinary fever.
Common Mistakes Parents Make
Mistake 1: Treating one number as a universal rule. Better: always connect the number to the child’s age and measurement site.
Mistake 2: Looking only at the thermometer. Better: look at your child’s behavior, hydration, breathing, and overall condition.
Mistake 3: Assuming a lower fever means everything is fine. Better: notice whether your child still acts sick or is getting worse.
Mistake 4: Blaming a true fever on teething. Better: remember that teething does not cause a true fever.
Mistake 5: Using an infant threshold for an older child. Better: keep age-specific guidance attached to the population it actually describes.
Mistake 6: Turning fever into a diagnosis. Better: use fever as one piece of information. This article does not attempt to identify the infection causing it.
A Simple Fever Check
When your child has a fever, pause before reacting to the number.
Age → Measurement → Temperature → Behavior → Trajectory
- Age. How old is your child?
- Measurement. Where was the temperature taken?
- Temperature. What exactly did the thermometer show?
- Behavior. Are they drinking and interacting, or do they look unusually ill?
- Trajectory. Are they improving, staying the same, or getting worse?
That sequence gives you a much more useful picture than the number alone.
If the Question Is Really About School
Understanding a fever and deciding whether to send a child to school are two different questions. If what you actually need to work out is whether to keep your child home for the day, see our guide to when to keep your child home from school.
Your Success Marker
You do not need to memorize every fever number.
A successful fever check means you can answer five questions:
- How old is my child?
- Where did I measure the temperature?
- What was the exact reading?
- How is my child acting?
- Is the situation improving or getting worse?
If you can answer those questions, you have moved from reacting to a number to understanding the situation.
The Bottom Line
A fever can be part of the body’s response to illness, and the temperature itself is only one part of the picture.
For parents, the most useful approach is to connect the temperature with the measurement site, the child’s age, and the child’s overall condition.
And remember: 100.4°F is not a universal fever rule that can be applied to every child in exactly the same way.
If your child is very young, has a concerning symptom, remains sick after the fever comes down, or seems to be getting worse, contact the pediatrician rather than relying on the number alone.
Sources
- American Academy of Pediatrics / HealthyChildren.org — Fever: When to Call the Pediatrician.
- American Academy of Pediatrics / HealthyChildren.org — Fever and Your Baby. Updated September 23, 2025.
This article provides general parent education based on the cited AAP sources. It does not diagnose the cause of a child’s fever and does not provide medication dosing. It is not a substitute for advice from your child’s healthcare provider. If your child has severe, unusual or worsening symptoms, contact a healthcare professional.
