At a glance
- A baby younger than 3 months with a temperature of 38°C (100.4°F) or higher needs urgent medical assessment, even if the baby seems well. Contact a clinician now; do not delay assessment to try fever medicine or finish this diary.
- Call your local emergency number for severe breathing difficulty, blue or grey lips, a child who is hard to wake or confused, an ongoing seizure, or fever with a stiff neck or a purple or bruiselike rash that does not fade with pressure.
- A temperature of 38°C (100.4°F) or above is generally considered a fever. Readings depend on the measurement method; record the actual number, unit and site without adding or subtracting degrees.
- Offer frequent fluids and continue breast-milk or formula feeds for infants. Keep clothing comfortable, allow rest and check the child regularly, including overnight. Avoid ice baths, alcohol rubs and excessive wrapping; observe drinking, urine and alertness.
- Children with sickle cell disease, weakened immunity, cancer treatment or a clinician’s special fever plan need immediate contact with their care team when fever is suspected. Follow that plan’s threshold and destination; a reassuring appearance or a lower temperature after medicine does not remove the need for assessment.
- Contact the clinician if fever lasts more than 24 hours in a child under 2 years, or more than 3 days (72 hours) at age 2 years or older. Seek help sooner for any warning sign or concern.
- Do not use ibuprofen below 6 months unless the child’s clinician directs it; avoid it when the child is dehydrated. Do not use aspirin for a child’s fever. Do not routinely alternate acetaminophen (paracetamol) and ibuprofen; use an alternating schedule only if a clinician gives clear instructions.
What the temperature can tell you
Fever is a sign of illness, not a diagnosis. The child’s age, breathing, alertness and drinking help determine the next step; the temperature alone cannot show how serious an illness is.
A temperature of 38°C (100.4°F) or above is generally considered a fever. Readings depend on the measurement method; record the actual number, unit and site without adding or subtracting degrees.
When medical assessment is needed
Call your local emergency number for severe breathing difficulty, blue or grey lips, a child who is hard to wake or confused, an ongoing seizure, or fever with a stiff neck or a purple or bruiselike rash that does not fade with pressure.
A baby younger than 3 months with a temperature of 38°C (100.4°F) or higher needs urgent medical assessment, even if the baby seems well. Contact a clinician now; do not delay assessment to try fever medicine or finish this diary.
Seek prompt medical advice if drinking is difficult, urine or wet diapers decrease substantially, the child is getting worse, or temperature repeatedly exceeds 40°C (104°F). Young-infant fever and any special fever plan need earlier action; do not wait for the duration limits below. Seek urgent medical advice after a seizure, even if it has stopped.
Children with sickle cell disease, weakened immunity, cancer treatment or a clinician’s special fever plan need immediate contact with their care team when fever is suspected. Follow that plan’s threshold and destination; a reassuring appearance or a lower temperature after medicine does not remove the need for assessment.
Measure and record consistently
Use a digital thermometer and follow its instructions. A rectal reading is most accurate in young infants; ask your clinician about the appropriate method if uncertain. Ear thermometers are unreliable below 6 months, and oral measurement usually requires age 4 years or older. If there is a special fever plan, use the measurement method recommended by the care team.
Touch alone, forehead strips and an underarm reading cannot reliably exclude fever. If a young baby feels hot or seems unwell, contact a clinician even if the reading is unclear; do not delay help to obtain a perfect measurement.
Comfort and fluids
Offer frequent fluids and continue breast-milk or formula feeds for infants. Keep clothing comfortable, allow rest and check the child regularly, including overnight. Avoid ice baths, alcohol rubs and excessive wrapping; observe drinking, urine and alertness.
Medicine safety
Fever medicine is for discomfort, not for making every temperature normal. Use a suitable single-ingredient product only with the correct weight-based instructions and measuring device. Ask a clinician or pharmacist if unsure; this diary does not calculate a dose or recommend another dose.
Do not use ibuprofen below 6 months unless the child’s clinician directs it; avoid it when the child is dehydrated. Do not use aspirin for a child’s fever. Do not routinely alternate acetaminophen (paracetamol) and ibuprofen; use an alternating schedule only if a clinician gives clear instructions.
When fever continues
Contact the clinician if fever lasts more than 24 hours in a child under 2 years, or more than 3 days (72 hours) at age 2 years or older. Seek help sooner for any warning sign or concern.
Record the reading and how the child is behaving, drinking and urinating. Share the diary with the clinician and follow their review plan. A lower reading after medicine does not prove the illness is mild or cancel warning signs.
Common questions
What temperature counts as a fever?
A temperature of 38°C (100.4°F) or above is generally considered a fever. Readings depend on the measurement method; record the actual number, unit and site without adding or subtracting degrees.
When is fever urgent in a young baby?
A baby younger than 3 months with a temperature of 38°C (100.4°F) or higher needs urgent medical assessment, even if the baby seems well. Contact a clinician now; do not delay assessment to try fever medicine or finish this diary.
How long can I wait before calling about fever?
Contact the clinician if fever lasts more than 24 hours in a child under 2 years, or more than 3 days (72 hours) at age 2 years or older. Seek help sooner for any warning sign or concern.
Should every fever be lowered with medicine?
Fever medicine is for discomfort, not for making every temperature normal. Use a suitable single-ingredient product only with the correct weight-based instructions and measuring device. Ask a clinician or pharmacist if unsure; this diary does not calculate a dose or recommend another dose.
Can I alternate fever medicines?
Do not use ibuprofen below 6 months unless the child’s clinician directs it; avoid it when the child is dehydrated. Do not use aspirin for a child’s fever. Do not routinely alternate acetaminophen (paracetamol) and ibuprofen; use an alternating schedule only if a clinician gives clear instructions.
Sources
- AAP — Fever without fear
- AAP — Taking a child’s temperature
- AAP — Ibuprofen safety for fever and pain
- NHS — Fever in children
- CDC — Sickle cell disease and fever
Written for Pedemy in our own words from the sources above; checked October 2026. For education only, not medical advice. Pedemy is independent and not affiliated with or endorsed by the organizations cited.