Fever in children and babies: when to worry and when to go to the ER
Is this an emergency?
This is not an emergency service. Call 911 or go to the nearest emergency room if you have:
- A baby under 3 months with 100.4 °F (38.0 °C) or higher
- Spots on the skin that do not fade when pressed, with a fever
- A seizure, a stiff neck, or being very hard to wake
- Grunting, the chest pulling in, flaring nostrils or bluish lips
- Signs of severe dehydration: barely peeing, sunken eyes, cold hands
- A bulging soft spot, or a weak, high-pitched or nonstop cry in a baby
- Green or bloody vomit
- Dengue warning signs
Help lines:
- 911 — Emergencies
- 1-800-981-0023 — Línea PAS (mental-health crisis line)
- 988 — Suicide & Crisis Lifeline
- 1-800-222-1222 — Poison Help
A fever in children is a temperature of 100.4 °F (38.0 °C) or higher, and it is usually a viral infection the body fights off on its own. What matters most is your child's age and how they look. A baby under 3 months with a fever needs the emergency room. We do not see babies under 6 months. In older children, watch for warning signs and how many days the fever lasts.
- Cold, cough or flu — fever with a runny nose, cough or aches
- Flu (influenza) — sudden high fever with aches and tiredness
- Ear pain or ear infection — fever with ear pain; confirming it needs an in-person look at the eardrum
- Hand, foot and mouth disease — fever with mouth sores and spots on hands and feet
- Diarrhea and vomiting — fever with vomiting or diarrhea; watch for dehydration
- Dengue — fever with body or eye pain; keep watching as the fever falls
- Urinary tract infection — young children need an in-person urine test
What is a fever in children, and how do you measure it?
A fever is a temperature of 100.4 °F (38.0 °C) or higher. The fever itself is not dangerous: it is a sign the body is fighting an infection.
Use a digital thermometer, never a mercury one. For babies, a rectal reading is the most accurate. Forehead (temporal artery) thermometers work at any age, ear thermometers from 6 months, and oral readings only from age 4. Forehead strips and armpit readings are less reliable. Write down each reading, the time and any medicine you gave.
Babies under 6 months: we do not see them by video
We see children from 6 months old. If your baby is under 3 months and has a temperature of 100.4 °F (38.0 °C) or higher, go to an emergency room or call 911, even if the baby seems fine and even in the middle of the night; do not wait for an appointment. If your baby is 3 to 6 months old and has a fever, call your baby's regular doctor or get seen in person, especially at 102.2 °F (39 °C) or higher.
Fever in babies 6 to 12 months: warning signs
Go to the ER or call 911 if your baby has a fever and:
- Has a weak, high-pitched or nonstop cry, or is very hard to wake.
- Has a bulging soft spot (fontanelle).
- Has fewer than 6 wet diapers a day and seems listless.
- Is vomiting green or bloody fluid, or cannot keep fluids down.
- Is grunting, has the chest pulling in with each breath, or has bluish lips.
Fever in children 1 to 5 years: warning signs
Go to the ER or call 911 if your child has a fever and:
- Makes a high-pitched noise when breathing at rest (stridor).
- Is drooling heavily or cannot swallow.
- Is peeing only once or twice a day, or has sunken eyes or cold hands.
- Has a seizure, is very listless or is not responding normally.
- Has spots on the skin that do not fade when you press a glass on them.
Fever in children 6 to 17 years: warning signs
Go to the ER or call 911 if your child has a fever and:
- A severe headache with a stiff neck.
- Severe pain in the lower right side of the belly.
- Testicular pain.
- Shortness of breath, or an asthma attack that does not improve with their inhaler.
- Dengue warning signs: belly pain, repeated vomiting, or bleeding from the nose or gums.
How many days of fever is too long?
Even if your child looks well, get an in-person evaluation if:
- Your child is under 2 and the fever lasts more than 24 hours without a clear cause. A urine test may be needed, and that cannot be done by video.
- Your child is 2 or older and the fever lasts more than 3 days (72 hours).
- The fever lasts 5 days or more, at any age.
- The temperature keeps rising above 104 °F (40 °C).
Dengue in children in Puerto Rico
Dengue hits children and teens hard on the island: in 2024, 10- to 19-year-olds were 29.3% of cases, according to the CDC. Warning signs usually appear 24 to 48 hours after the fever goes away, so keep watching your child once it breaks. If dengue is possible, use acetaminophen and do not give ibuprofen. Read our dengue warning signs guide.
Home care and fever medicines
If your child has a fever and no warning signs:
- Offer fluids often and let them rest.
- Acetaminophen or ibuprofen can make your child more comfortable; you do not need to treat the number if they are resting comfortably.
- Dose by weight, not just age. Use the syringe or cup that comes with the medicine, never a kitchen spoon.
- Do not give acetaminophen under age 2 without a doctor's guidance, and do not give ibuprofen to babies 6 months or younger.
- Never give aspirin to a child unless their doctor tells you to.
- Do not overdress them.
When can a video visit help with your child's fever?
An online doctor visit can help if your child is 6 months or older, looks well between fever spikes, and the fever has a likely cause, such as a cold or cough, hand, foot and mouth disease or diarrhea and vomiting without dehydration. The doctor will assess your child, help with weight-based dosing and assess whether an in-person visit is needed. If appropriate, the doctor can prescribe medication. We do not prescribe controlled substances.
Dr. Diana Nieves Castro is a general practice physician and is not a pediatrician. Some things cannot be done by video, such as confirming an ear infection or strep and urine tests. A parent with patria potestad or a legal guardian must be on camera for the whole visit. See the child doctor visit and how to prepare your child.
Frequently asked questions
- What temperature is a fever in a child?
- 100.4 °F (38.0 °C) or higher. More than the number itself, what matters is your child's age, how they look and how long the fever lasts.
- What should I do if my 2-month-old has a fever?
- Go to an emergency room or call 911. In a baby under 3 months, a temperature of 100.4 °F (38.0 °C) or higher is an emergency, even if the baby seems fine. We do not see babies under 6 months.
- How many days of fever is normal for a child?
- Get your child checked if a fever lasts more than 24 hours under age 2, or more than 3 days at age 2 or older. After 5 days of fever, a doctor should always see your child in person.
- Can I alternate acetaminophen and ibuprofen?
- Ask a doctor before alternating them, because it is easy to mix up doses. Work out each dose from your child's weight, use the measuring device that comes with the medicine, and never give aspirin.
Sources
- Fever (MedlinePlus, U.S. National Library of Medicine) (accessed 2026-09-30)
- Fever in under 5s: assessment and initial management, NG143 (NICE) (accessed 2026-09-29)
- How to take a child's temperature (AAP, HealthyChildren.org) (accessed 2026-09-30)
- Acetaminophen dosing for fever and pain in children (AAP, HealthyChildren.org) (accessed 2026-09-30)
- Dengue: warning signs and treatment (CDC) (accessed 2026-09-30)
- Dengue in Puerto Rico, 2024 (CDC MMWR 74(5)) (accessed 2026-09-29)