Baby health
1 to 2 minutes to measure the temperature and check for warning signs
5 steps
When to seek medical care for a baby with a fever depends mainly on the baby's age, how the temperature was measured, and their overall condition. In a baby under 3 months, a temperature of 100.4°F (38°C) or higher requires immediate medical evaluation; for newborns, follow healthcare guidance for underarm measurements and do not wait if the baby appears unwell. Use a digital thermometer and observe breathing, feeding, alertness, and urination. Difficulty breathing, seizures, or difficulty waking are emergency warning signs.
What is a fever and why does age matter?
Fever is a sign that the body is responding to a condition, often an infection. It does not reveal the cause on its own. Body temperature can also rise because of factors such as excessive clothing or a very warm environment, so it is important to measure it correctly and consider the baby's overall condition.
Age affects how urgently the baby needs to be evaluated. Babies under 3 months require prompt medical evaluation when they have a fever because some serious infections may begin with few symptoms. In newborns, a low temperature or unusual behavior can also be concerning. If the baby was born prematurely or has a health condition, follow the individual guidance provided by the healthcare team caring for them.
How to measure a baby's temperature
Use a digital thermometer and follow the manufacturer's instructions. Underarm measurement is a common option for families in Brazil: place the tip of the thermometer against the skin in the armpit and keep the baby's arm against their body for the recommended amount of time. Do not try to calculate an equivalent temperature by adding or subtracting degrees; values vary depending on the measurement site.
Feeling the forehead with your hand, looking at the skin, or using temperature strips does not confirm a fever. If the baby was heavily bundled, in a warm environment, or has just had a bath, the reading may be affected. If the baby appears well and has no warning signs, remove excess clothing, wait a few minutes, and measure again. Do not do this to delay medical care for a young baby who appears unwell.
Fever in babies under 3 months
In a baby under 3 months, a temperature of 100.4°F (38°C) or higher requires immediate medical evaluation, even if the baby is still feeding and appears relatively well. Contact a healthcare service or go to an urgent care facility; do not wait until the next day to see whether it improves.
For newborns under 2 months, the Brazilian Ministry of Health also classifies an underarm temperature of 99.5°F (37.5°C) or higher as a warning sign. Because temperature values vary depending on where they are measured and recommendations may differ, tell the healthcare team exactly where and how you measured the temperature. Do not give fever-reducing medication before receiving guidance.
Emergency warning signs beyond the thermometer reading
Seek urgent medical care if the baby is breathing with effort or very rapidly, has pauses in breathing, has bluish or purple lips or skin, experiences a seizure, or is difficult to wake. A rash that does not fade when pressed, a very weak or high-pitched cry, refusal to feed, and decreased urination also require prompt attention.
A low temperature can also be a warning sign in a young baby, especially if the baby feels cold, is very sleepy, or is less responsive than usual. If the condition appears serious, contact your local emergency medical service. Do not wait for every symptom to appear; a single significant warning sign may be enough to justify urgent care.
What to do while seeking guidance
Dress the baby in comfortable clothing without excessive blankets and keep the environment at a comfortable temperature. Continue offering the usual feedings and observe whether the baby feeds and urinates. Write down the temperature, time, measurement site, and when the symptoms began; this information can help the healthcare team.
Do not use cold baths, ice-cold compresses, alcohol on the skin, teas, or home remedies to lower the temperature. Fever-reducing medications should be used according to professional guidance, with a product and dose appropriate for the baby's age and weight. Do not alternate medications or assume that the baby is out of danger just because the temperature temporarily improves.
Fever after vaccination or with other symptoms
An elevated temperature may occur after vaccination, but this does not confirm that the vaccine is the cause in every case. Write down when the vaccine was given and tell the healthcare team. In a baby under 3 months, a fever of 100.4°F (38°C) or higher still requires immediate evaluation.
Cough, runny nose, vomiting, diarrhea, skin rash, or changes in feeding can help the healthcare professional investigate the cause. Do not attribute a fever to teething, warm clothing, or vaccination without considering the baby's age and overall condition. If the baby is getting worse, seek medical care even if the thermometer does not show a very high temperature.
Why a fever can return
Body temperature may rise and fall during an illness. A fever-reducing medication may lower it temporarily without treating the underlying cause, and another increase does not automatically mean that the medication failed or that the infection has become more serious. For older children, discomfort and behavior also matter; in very young babies, age makes prompt evaluation necessary.
There is no duration of fever that, by itself, can determine its severity or cause. Follow the guidance you receive and seek reevaluation if new signs appear, if the baby stops feeding, becomes unusually lethargic, or develops difficulty breathing. For babies under 3 months, do not wait for the fever to persist for several days before seeking help.
What to do if you suspect a fever
Measure correctly, consider the baby's age, and seek care promptly when warning signs are present
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Check the baby's overall condition first
Check whether the baby is breathing without effort, responding as usual, feeding normally, and maintaining their usual skin color. If the baby is difficult to wake, has bluish or purple lips, has a seizure, or has difficulty breathing, seek emergency medical care immediately; do not delay care to measure the temperature again.
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Measure with a digital thermometer
Use a digital thermometer and follow the device instructions. In Brazil, underarm measurement is common: place the tip in contact with the skin and keep the baby's arm against their body for the recommended amount of time. Do not estimate temperature by touching the forehead or use temperature strips. Record the reading and where it was measured.
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Consider the baby's age and measurement site
Interpret the reading based on the baby's age and where the temperature was measured. In babies under 3 months, a temperature of 100.4°F (38°C) or higher requires immediate evaluation. For newborns, seek guidance promptly if the underarm temperature is outside the range provided by the maternity hospital or healthcare team; the Brazilian Ministry of Health considers an underarm temperature of 99.5°F (37.5°C) or higher a warning sign in babies under 2 months.
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Consider factors that may affect the reading
If the baby was heavily bundled or has just had a bath, remove excess clothing and wait a few minutes before measuring again, provided the baby appears well and has no warning signs. Do not wait for a second reading if the baby is very young, unusually lethargic, or has difficulty breathing, feeding, or waking.
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5
Seek medical care and provide the details
Contact the pediatrician or go to a healthcare facility based on the baby's age and the signs you observe. In babies under 3 months, do not try to manage the fever at home before obtaining medical guidance. Report the temperature, how it was measured, when it started, and whether there are other symptoms. If there are severe warning signs, contact your local emergency medical service.
Fever in babies: when to seek help
Important Tips
Write down the temperature, the time, and where it was measured so you can provide this information to the healthcare team.
Bring the Child Health Record and mention whether the baby was born prematurely, has any health condition, or recently received a vaccine.
Continue offering the baby's usual feedings and observe whether the baby continues to urinate.
Avoid overdressing or using too many blankets, but do not allow the baby to become cold or shiver.
Do not use alcohol, cold baths, ice-cold compresses, or medications without professional guidance.
Frequently asked questions
Quick answers to common questions.
How can I tell if my baby has a fever without a thermometer?
Touching the baby may suggest that they feel warmer, but it does not measure temperature accurately. Use a digital thermometer according to the manufacturer's instructions. In babies under 3 months, a temperature of 100.4°F (38°C) or higher requires immediate medical evaluation; for newborns, also follow your healthcare team's guidance regarding underarm temperature measurements.
Do I need to add degrees when measuring temperature under the arm?
No. Temperature varies depending on where it is measured. Do not add or subtract degrees to try to convert a reading. Record the temperature, where it was measured, and provide this information to the healthcare professional, especially if the baby is a newborn.
Is a fever after a baby's vaccination always normal?
A fever may occur after a vaccination, but do not automatically assume that any elevated temperature is caused by the vaccine. In babies under 3 months, a temperature of 100.4°F (38°C) or higher requires immediate evaluation. Tell the healthcare provider which vaccine was given and when.
Can I give fever-reducing medicine to a baby with a fever?
Do not give fever-reducing medication without guidance, especially to a baby under 3 months. The baby's age and weight, the medication, and the product concentration all affect how it should be used. Do not alternate medications or use home remedies.
Does a high fever mean the infection is serious?
Not necessarily. The number on the thermometer alone does not identify the cause or determine the severity. Also observe the baby's breathing, alertness, feeding, urination, and skin color. In young babies, even appearing relatively well does not eliminate the need for evaluation when the temperature reaches a warning threshold.
Which signs along with fever require urgent medical care?
Difficulty breathing, bluish or purple skin or lips, seizures, difficulty waking, refusal to feed, or a rash that does not fade when pressed are signs that require urgent medical care. If the baby appears very unwell, call your local emergency medical service.
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Sources consulted
- Brazilian Ministry of Health — Integrated Management of Childhood Illness: Neonatal IMCI
- Brazilian Society of Pediatrics — Management of Acute Fever
- Fiocruz — Key Questions About Fever Management in Pediatric Emergency Care
- NHS — How to take your baby's temperature
- NHS — When to get urgent medical help for babies and children under 5