Quick answer: In children, a fever is a temperature of 100.4°F (38°C) or higher. That single number is the medical cutoff at every age — but what you should do about it depends far more on your child’s age and how they are acting than on the reading itself.
The Number That Defines a Fever
A fever is 100.4°F (38°C) or above, measured rectally, orally, or with a reliable forehead or ear thermometer. Anything below that is not a fever, even if your child feels warm to the touch.
Parents often assume a higher number means a more serious illness. It usually does not. A child with a 104°F fever who is drinking, alert, and playing between doses of medicine is frequently less concerning than a listless child at 101°F. Fever is the immune system working, not the disease itself.
Age Changes Everything
The same 100.4°F reading carries very different weight depending on how old your child is:
- Under 3 months: A rectal temperature of 100.4°F or higher is a medical emergency. Call us or go to the emergency department the same day, even if the baby seems fine otherwise. Young infants cannot localize infection, and serious causes can look mild at first.
- 3 to 6 months: Call your provider for any fever. A reading above 102°F warrants prompt evaluation.
- 6 months to 2 years: A fever lasting more than 24 hours without an obvious cause should be checked.
- Over 2 years: Behavior matters more than the number. Watch how your child drinks, breathes, and responds to you.
Taking an Accurate Temperature
The method matters, especially in young children:
- Rectal is the most accurate under age 3 and is the standard for infants.
- Oral works from about age 4, once a child can hold the thermometer under the tongue with a closed mouth. Wait 15 minutes after hot or cold drinks.
- Axillary (armpit) readings run roughly a degree low and are best used as a screen, not a decision point.
- Temporal and tympanic thermometers are convenient but sensitive to technique. Confirm a surprising reading with a second method.
Skip mercury thermometers entirely — they are a breakage and exposure hazard.
Treating a Fever at Home
Treat the child, not the thermometer. If your child is comfortable, medication is optional.
- Acetaminophen can be used at any age, dosed by weight, no more often than every 4 to 6 hours.
- Ibuprofen is an option from 6 months of age, dosed by weight, every 6 to 8 hours.
- Never give aspirin to a child or teenager. It is linked to Reye’s syndrome, a rare but serious condition affecting the liver and brain.
- Offer fluids steadily. Dehydration, not the fever, is the common complication.
- Dress your child lightly. Bundling traps heat. Cold baths and rubbing alcohol are unsafe and cause shivering, which raises core temperature.
Always dose by your child’s current weight rather than age, and confirm the concentration on the bottle — infant and children’s formulations differ.
When to Call a Provider
Contact us promptly if your child has:
- Any fever under 3 months of age
- A fever lasting more than three days
- A stiff neck, severe headache, or a rash that does not blanch when pressed
- Trouble breathing, or breathing that looks fast or labored
- Signs of dehydration: no wet diaper in 8 hours, no tears, a dry mouth, or sunken eyes
- Unusual drowsiness, difficulty waking, or persistent irritability when held
- A seizure
- A fever that returns after several fever-free days
Children with chronic conditions such as asthma or a weakened immune system should be evaluated earlier rather than later.
Frequently Asked Questions
Is a fever of 104°F dangerous by itself?
A high number is uncomfortable but not inherently harmful in an otherwise healthy child. Fevers from infection rarely climb past 106°F. How your child looks and acts is the better guide, and a persistent 104°F reading is still worth a call.
What is a febrile seizure?
A febrile seizure is a convulsion triggered by a rapid rise in temperature, most often between 6 months and 5 years. It is frightening to witness but usually brief and harmless. Lay your child on their side, do not put anything in their mouth, and call us. A first-time seizure should always be evaluated.
Should I wake my child to give fever medicine?
Generally no. Sleep is more valuable than a lower number. Treat when your child wakes uncomfortable.
Can teething cause a fever?
Teething may raise temperature slightly but does not cause a true fever of 100.4°F or higher. Look for another cause.
Get Your Child Seen Today
If a fever is worrying you, do not wait it out alone. IM&PC sees patients of every age at both of our Mississippi clinics — New Albany and Saltillo. Call to schedule, or walk in during urgent care hours.
This article is general health information from Internal Medicine & Pediatric Clinic and is not a substitute for individual medical advice. Talk with your provider about your own situation. If you think you are facing a medical emergency, call 911.