A newborn has a fever when a rectal temperature reaches 100.4°F (38°C) or more—check with a digital thermometer and call your pediatrician.
Telling If Your Newborn Has A Fever: Clear Signs
Touch can hint, but numbers settle it. Feel the chest or back: warm skin, flushed cheeks, and fast breathing can cue you to check. Then measure. For babies under three months, a rectal reading gives the most reliable number. If the result is 100.4°F, which equals 38°C, or higher, treat it as a fever and contact your doctor without delay.
Quick Reference: Thermometer Methods And Fever Threshold
| Method | Best For | What Counts As Fever |
|---|---|---|
| Rectal (digital) | Newborns to toddlers | ≥ 100.4°F (38°C) |
| Forehead/Temporal | Any age screening | Follow device guide; confirm rectally in young babies |
| Armpit/Axillary | Any age screening | Less accurate; confirm with rectal reading |
For step-by-step technique, see the AAP guide to taking a child’s temperature.
How To Check A Newborn’s Temperature Safely
Gather a digital rectal thermometer, water-based lubricant, and a clean cloth. Wash your hands. Lay your baby on the back or tummy across your lap. Steady the hips with a hand. Turn on the device, then:
- Place a small dab of lube on the tip.
- Slide the tip into the anus about ½ inch to 1 inch. Stop if you meet resistance.
- Keep your hand on your baby’s thighs so the thermometer stays still.
- Wait for the beep, remove, and read the number.
- Clean the tip with soap and water, then rinse and dry.
Skip mercury devices. Ear readings can miss fevers in small babies. Armpit and forehead tools help for a quick check, yet a rectal number settles doubt in newborns.
Pick a flexible-tip infant model. Keep one thermometer for rectal use only. Clean the handle and store it in a case. If your baby wiggles, pause and restart when calm.
Newborn Fever Symptoms You Might Notice
Numbers guide treatment, yet body cues help you decide when to measure. Watch for poor feeding, fewer wet diapers, sleepiness that is hard to break, unusual fussing, cool hands with a hot core, or a look that seems off. If any of these show up, take a temperature and write the reading down. Chills, a whimpering cry, or a fontanelle that seems tense can be early clues too. Trust your sense of change from your baby’s usual rhythm—parents often notice shifts before numbers climb. Write what you see. Keep notes handy.
When To Call The Doctor Or Go In
Age matters. For babies under three months, any rectal reading at or above 100.4°F needs a same-day call to your pediatrician. If your baby is hard to wake, breathing fast, turns blue or gray, has a stiff neck, a bulging soft spot, a seizure, or a rash that spreads, seek urgent care now.
For babies three to twelve months, call if the fever reaches 102.2°F (39°C), lasts longer than a day, or your child looks unwell. Trust your gut; if something feels wrong, reach out.
Clear national advice backs these cutoffs. See the NHS guidance on high temperatures in children for a plain view of thresholds and red flags.
Medication Rules For Small Babies
Do not give fever reducers to a newborn unless your doctor tells you to. For older babies, your doctor may suggest acetaminophen based on weight. Avoid aspirin for anyone under nineteen. If your baby throws up medication or spits it out, call for dosing advice rather than repeating doses on your own.
Ask your pediatrician about dosing by weight. Ibuprofen is often held until older; acetaminophen is the usual first choice. After vaccines, your doctor may still want to see a newborn with a true fever.
What Not To Do
- No ice baths or rubbing alcohol. Both can drop body temperature too fast and cause harm.
- No bundling or heavy blankets. Overheating can push a mild fever higher.
- No cough and cold combos. Many are not meant for babies.
- No honey for babies under one year due to botulism risk.
Comfort Steps That Help
Offer breast milk or formula often. Small, frequent feeds prevent dehydration. Keep clothing light and breathable. Use a lukewarm sponge bath if your baby seems uncomfortable, then dry and dress lightly. Hold your baby upright to ease breathing. Keep the room cool, around 68–72°F, and run a clean humidifier if the nose is stuffy.
Clear a stuffy nose with saline drops and a soft bulb syringe. Offer a pacifier if it helps. For naps, place your baby on the back in a crib without loose bedding.
Why Rectal Readings Matter In Newborns
Young babies can look fine yet carry a serious bug. Rectal readings track core heat and perform better than armpit or forehead checks at this age. That is why many pediatric groups teach rectal measurement as the gold standard for infants. It reduces guesswork and speeds up the right next step when a number crosses 100.4°F.
Common Newborn Fever Scenarios
Right After Shots
A mild rise can follow routine vaccines. If your baby is under three months and the rectal reading hits 100.4°F, call your pediatrician. Report the timing and any other symptoms such as poor feeding or unusual crying.
After A Long Car Ride Or Warm Room
Overheating can push a reading up. Cool the room, remove layers, and wait ten minutes. Then recheck. If the number stays high or climbs, treat it as a true fever.
Teething
Teething can cause drool and fussing, but high temperatures are linked to other causes. If the rectal reading says 100.4°F or more, act on it like any other fever.
Temperature And Action Planner
| Rectal Temperature | Age | Action |
|---|---|---|
| 99–100.3°F (37.2–37.9°C) | Any | Recheck in 15–30 minutes; adjust layers and room |
| ≥ 100.4°F (38°C) | 0–3 months | Call pediatrician the same day; follow advice |
| 102.2°F (39°C) or higher | 3–12 months | Call if it lasts more than a day or baby looks unwell |
| Any fever with red flags | Any | Seek urgent care now |
When A Fever Means An Emergency
Seek care now for any baby with a fever and one or more of these signs: weak cry, limp body, trouble breathing, lips or face turning blue, nonstop vomiting, seizure, purple rash, stiff neck, bulging fontanelle, or signs of dehydration such as no tears and far fewer wet diapers.
How Doctors Evaluate A Newborn With Fever
Your doctor will ask about birth history, feeding, diapers, contacts with sick people, recent travel, and vaccine dates. Expect a full exam. Tests may include a nasal swab for viruses, blood work, urine tests, or a chest X-ray. The plan depends on age, exam findings, and test results. Many babies go home with follow-up. Some are watched in the hospital for close monitoring and treatment.
Practical Tips To Track And Share Details
- Log the time, the number, and the method each time you check.
- Note feeds, diapers, sleep, and behavior in the same place.
- Bring the thermometer to the visit so you can show the model used.
- Pack a spare outfit, diapers, and a swaddle for visits or urgent care.
When you call, share the highest number, how you measured it, any medicine given, and red flags. Many offices have nurse lines for same-day guidance.
Keeping Fevers At Bay
Wash hands before feeds and after diaper changes. Keep sick contacts away. Stay current on your baby’s shots and maternal boosters where advised. Keep indoor smoke away from your baby. Use safe sleep gear so babies do not overheat during naps and night.
Plain Takeaway For Worried Parents
If your newborn feels hot, measure a rectal temperature with a digital device. A reading of 100.4°F (38°C) or higher is a fever. Under three months, call your pediatrician the same day. Trust your sense and seek help fast if red flags show up. Clear steps and calm action keep babies safe.