Baby Fever: When to See a Doctor and What to Do at Home
Dra. Paula Andrade
CRM-SP 204778 | RQE 131771 | Título SBP 2024
Licensed in Brazil — Itaim Bibi, São Paulo
Your child has a fever and you are not sure whether to rush to the emergency room NOW or if you can wait. This is the question I receive most often — including late-night WhatsApp messages! In this guide, I will teach you exactly when a fever is an emergency and when you can safely monitor at home. If you are an expat family in Sao Paulo, check our guide to pediatric care in Brazil for helpful context on the healthcare system.
Quick Summary (If You Are in a Hurry)
→Baby 0-3 months with fever: Go to the ER or pediatrician IMMEDIATELY
→Over 3 months: Watch for warning signs (listed below)
→Fever is not a disease— it is the body's defense against infection
→More important than the number on the thermometer is how your child is behaving
Baby Temperature Chart: What Each Reading Means
Axillary (armpit) measurement — reference values. See our complete temperature chart by age for more detail.
| Temperature | Classification | What to Do |
|---|---|---|
| 35.5-36.4°C (95.9-97.5°F) | Normal (low) | Normal. Bundle up if the room is cold. |
| 36.5°C (97.7°F) | Normal | NOT a fever. Perfectly normal temperature. |
| 37.0°C (98.6°F) | Normal | NOT a fever. Within normal range. |
| 37.5°C (99.5°F) | Low-grade | Upper limit. Observe and re-measure in 30 minutes. |
| 37.8°C (100.0°F) | Fever | Fever. Give medication if the child is uncomfortable. |
| 38.0-39.4°C (100.4-102.9°F) | Moderate fever | Medicate, hydrate, and watch for warning signs. |
| 39.5°C+ (103.1°F+) | High fever | Medicate and seek medical evaluation if no improvement. |
| 40°C+ (104°F+) | Hyperthermia | Seek medical attention immediately. |
Source: Brazilian Society of Pediatrics (SBP). Axillary measurement. Rectal readings are approximately 0.5°C / 1°F higher.
What Is Fever? (And Why It Happens)
Fever is not a disease— it is a symptom. It is your child's body fighting an infection. The body raises its temperature to create a hostile environment for viruses and bacteria. In most cases, fever is a sign that the immune system is working correctly.
Understanding when to take your baby to the pediatrician goes beyond just fever — it involves observing the overall picture.
When Fever Is an Emergency
Go to the ER Immediately If:
- Baby under 3 months with any fever (37.8°C / 100°F or above)
- Purple or red spots on the skin (petechiae) — may indicate meningitis
- Difficulty breathing — rapid breathing, chest retractions, or grunting
- Seizure or abnormal movements
- Extremely lethargic baby — does not respond to stimulation
- Persistent vomiting with signs of dehydration
Worried about your baby's fever?
Dr. Paula can help you determine the right course of action. Appointments within 24-48 hours.
Talk to the PediatricianFever by Age: What to Do
Under 3 Months
Any fever (37.8°C / 100°F or above) is an emergency. Go to the ER or see your pediatrician immediately. At this age, the immune system is still immature, and infections can progress quickly.
3 to 6 Months
Fever above 39°C (102.2°F) or any fever with irritability or lethargy requires same-day pediatric evaluation.
Over 6 Months
Fever lasting more than 3 days, or above 39.5°C (103.1°F) that does not respond to fever medication, or accompanied by other concerning symptoms requires medical evaluation.
What to Do When Your Baby Has a Fever
What NOT to Do
- • Do NOT use rubbing alcohol on the skin
- • Do NOT give cold/ice baths
- • Do NOT alternate acetaminophen and ibuprofen without medical guidance
- • Do NOT give aspirin to children (risk of Reye syndrome)
Post-Vaccination Fever
It is common for babies to develop a mild fever after vaccinations. This is an expected immune response and usually resolves within 24-48 hours. Give acetaminophen if the baby is uncomfortable, and contact your pediatrician if the fever lasts longer than 48 hours or is accompanied by other symptoms.
A Note for Expat Families
In Brazil, fever medication dosing is weight-based, not age-based. Your pediatrician will calculate the exact dose for your child. Common medications available at any pharmacy include paracetamol (Tylenol) and dipirona (metamizole) — the latter is widely used in Brazil but not available in some countries. Dr. Paula can explain the differences and recommend the best option for your family. Learn more about consultation costs and insurance reimbursement.
Scientific References
- • Brazilian Society of Pediatrics (SBP). Scientific Document #206: Approach to Acute Fever in Pediatrics. 2025.
- • American Academy of Pediatrics. Fever and Antipyretic Use in Children. Pediatrics, 2011.
- • National Institute for Health and Care Excellence (NICE). Fever in Under 5s: Assessment and Initial Management. 2021.
Worried About Your Baby's Fever?
If your child has a fever and you are unsure what to do, contact Dr. Paula for guidance. Appointments available within 24-48 hours.
Consultório no Itaim Bibi, São Paulo | CRM-SP 204778 | RQE 131771
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