Health & Safety  ·  Newborn

Newborn Fever: When It's an Emergency (Print This)

My newborn feels hot. When is a fever an emergency?

It’s 2 a.m. and the rectal thermometer reads 100.4°F — do I go to the ER now? Take a deep breath. For a baby under 3 months, the rule is simple and clear: a rectal temperature of 100.4 F (38 C) or higher means you call the pediatrician or go to the ER right away, any time of day or night. At this age, infection can cause either a high OR a low temperature, so a baby running cold can be just as serious as one running hot.

4 min read Health & Safety Updated June 2026

Call 911 now if

  • Your baby stops breathing for longer than about 20 seconds, or has any breathing pause (even a short one) with a color change, limpness, or no response
  • Lips, face, or tongue look blue or gray, or your baby is gasping
  • Your baby is not breathing or not responding: call 911 right away and begin infant CPR now. The 911 dispatcher will talk you through each step, even if you have never done it
  • A seizure
  • Vomit that is green or yellow-green (bile), which can mean a bowel blockage and is a surgical emergency: go now
  • A jaundiced (yellow) baby who has a high-pitched cry with arching, stiffness, or limpness

Call your pediatrician right away if

  • Your baby is under 3 months old and has a rectal temp of 100.4 F (38 C) or higher, day or night, even if they seem fine otherwise. If you cannot reach your pediatrician, go to the ER
  • Your baby's rectal temp is below about 97.7 F (36.4 C), or your baby feels cold, looks mottled or pale and gray, has cold hands and feet, or is hard to warm. In young babies infection can cause a low temp, not just a high one
  • Fast breathing, grunting with each breath, flaring nostrils, or the skin pulling in around the ribs or neck (retractions). A breathing pause longer than about 20 seconds, or any pause with a color change or limpness, is a 911 emergency. Brief pauses under about 10 seconds with normal color can be normal newborn breathing
  • Hard to wake, very limp, or unusually drowsy
  • High-pitched, weak, or nonstop crying that you cannot soothe
  • Refusing to feed, or far fewer wet diapers than usual
  • Very pale lips, face, or skin (blue or gray color is a 911 emergency)
  • A rash that does not fade when you press on it
  • Stiffness in the neck
  • Forceful or projectile vomiting, vomit with blood, or repeated vomiting (green or yellow-green bile vomit is a go-now emergency, see above)
  • A bulging or sunken soft spot
  • Yellow skin or eyes in the first 24 hours of life (never normal that early), yellow spreading down to the belly, arms, legs, palms, or soles, or yellowing of the whites of the eyes; or a yellow baby who is sleepy, feeding poorly, or has a high-pitched cry

How to take a rectal temperature

  1. Step 1Use a digital thermometer made for rectal use. Clean the tip with soap and lukewarm water (or rubbing alcohol), rinse, and dry before use.
  2. Step 2Put a small dab of petroleum jelly on the tip.
  3. Step 3Lay your baby on their back and gently hold their thighs up toward the belly, or lay them tummy-down across your lap.
  4. Step 4Gently slide the tip about half an inch to one inch into the rectum. Stop if you feel resistance, never force it.
  5. Step 5Hold it still and keep a hand on your baby until it beeps. Remove it and read the number.
  6. Step 6Clean the thermometer with soap and lukewarm water or rubbing alcohol, rinse, and dry. Keep it labeled for rectal use only.

Before you call, jot these down

  • The exact rectal temperature and the time you took it
  • Your baby's age in weeks
  • How they are acting: feeding, alertness, breathing, crying
  • Any other symptoms: rash, vomiting (note the color), cough, fewer wet diapers, yellow skin or eyes
  • When you last gave any medicine (do not give fever medicine to a baby under 3 months unless a doctor tells you to)

You are not overreacting. With a young baby, calling early is exactly what the doctors want you to do. Trust your gut, and when in doubt, make the call.

Quick answers

Can I use a forehead or ear thermometer instead?
For a baby under 3 months, a rectal temperature is the most accurate and the one doctors rely on. Forehead and ear readings can miss a real fever at this age. If another method reads high, confirm with a rectal temp, but do not delay calling.
Should I give my newborn fever medicine first?
No. Do not give any fever medicine to a baby under 3 months unless your pediatrician tells you to. Call the doctor first. They need to know the true temperature, and a young baby needs to be checked, not just treated at home.
How do I know if my baby is getting dehydrated?
Watch for fewer wet diapers than expected, such as none in 6 or more hours, plus a dry mouth, no tears when crying, a sunken soft spot, dark urine, or a sleepy and floppy baby. Any of these in a baby under 3 months means call your pediatrician right away, day or night.

Sources & further reading

  1. American Academy of Pediatrics — HealthyChildren.org

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This guide reflects current AAP and CDC guidance and is for educational purposes only. It does not constitute medical advice. ParentFlow is a wellness companion — not a substitute for your pediatrician. For any medical concern, contact your healthcare provider.