Baby Fever Questions: 12 Short, Sourced Answers

What temperature counts as a fever in a baby?

The NHS defines it simply: "a high temperature is 38C or more." The AAP uses the same threshold in Fahrenheit for a rectal reading: 100.4°F (38°C) or higher "is considered a fever."

The AAP notes rectal readings are the most reliable in infants, especially under 3 months — armpit (axillary) readings tend to run lower and can miss a true fever.

Full fever guide →

Is 99.5°F a fever in a baby?

No. The clinical threshold both the NHS (38C) and AAP (100.4°F/38°C) use is higher than 99.5°F, so a reading of 99.5°F falls below the definition of fever.

Normal infant temperature naturally fluctuates through the day — it tends to run a little higher in the late afternoon and lower in the early morning — so a reading in the high 90s on its own isn't a red flag.

When a reading does need attention →

When should I call the doctor or go to the ER for a baby's fever?

Call 111/your doctor promptly, per the NHS, if your child "is under 3 months old and has a temperature of 38C or higher," or "is 3 to 6 months old and has a temperature of 39C or higher."

The AAP gives the equivalent US guidance: seek care if the baby "is younger than 3 months (12 weeks) and has a temperature of 100.4°F (38.0°C) or higher," or if, at any age, "temperature rises above 104°F (40°C) repeatedly." The NHS also flags a high temperature "that's lasted for 5 days or more" as a reason to call 111.

Full when-to-seek-help list →

Is a rash with a fever always an emergency?

A specific kind is: the NHS says to call 999 or go to A&E immediately if your child "has a rash that does not fade when you press a glass against it" — a classic sign doctors check for.

A rash alongside fever that doesn't have this "glass test" feature still isn't something to ignore — the NHS separately advises calling 111 if your child "has other signs of illness, such as a rash, as well as a high temperature." When in doubt, get it checked rather than waiting.

Is "cold hands and feet" during a fever a warning sign?

In the UK, yes — the NHS lists "unusually cold hands and feet" as one of its 999-level emergency signs for a feverish child, alongside a stiff neck, sensitivity to light, and skin that looks blue, grey, blotchy or paler than usual.

If your baby's hands and feet are cold while their core temperature is high, treat it the same as the NHS's other red-flag signs and seek urgent care rather than just adding a blanket.

Is a 102°F fever too high for teething?

A 102°F (38.9°C) reading isn't caused by teething at all — the AAP states plainly: "though many parents expect a fever when baby teeth start to break through, extensive studies show this is a false symptom of teething."

If your baby is teething and also running 102°F, treat the fever as a separate issue with its own cause (commonly a viral illness) rather than attributing it to the teeth, and follow the fever thresholds above for when to seek care.

Teething symptoms that are real →

Does teething actually cause fever?

No. The AAP's direct statement is that despite the common expectation, "extensive studies show this is a false symptom of teething."

The NHS's own list of common fever causes in children — coughs and colds, chickenpox, tonsillitis, vaccinations — doesn't include teething either. Mild gum discomfort or a very slightly warm feeling can go along with teething, but a true fever (100.4°F/38°C or higher) means something else is going on.

Should I take my baby to the ER for a 101°F fever?

Not necessarily on the temperature reading alone — for a baby over 3 to 6 months, 101°F (38.3°C) is below both the AAP's "above 104°F repeatedly" and the NHS's 999-level thresholds.

The exception is age: if your baby is under 3 months old, the NHS and AAP both say any fever at or above 38°C/100.4°F warrants prompt medical contact, not a wait-and-see approach — because, as the AAP explains, serious infections can look mild at that age.

See the full age-based thresholds →

How do I safely bring down my baby's fever at home?

Don't over-bundle: the NHS advises to "not cover them up in too many clothes or bedclothes," and an NHS trust patient page adds, "never tepid or cold sponge your child as this can cause shivering which can make their temperature rise further," and "never wrap a feverish child."

Offer fluids often and keep clothing light rather than trying to actively cool the skin — and confirm any medication dose with your pediatrician, based on your baby's weight rather than their age.

Full evidence-based fever-care tips →

Is fever after a vaccine normal, and how long does it last?

Usually yes, and usually brief. The AAP states "fever with most vaccines begins within 12 hours and lasts 1 to 2 days" — occurring in roughly 25% of babies after DTaP, 20% after flu vaccine, and 10% after MMR.

The AAP says to call if "fever lasts more than 3 days," "fever returns after being gone more than 24 hours," "fever [is] higher than 104°F (40°C)," or if it occurs "in baby less than 12 weeks old" — otherwise, a short, mild fever after a shot is an expected immune response, not a complication.

My baby has a fever and is vomiting — when is that serious?

For babies under 12 weeks, the AAP says to call the doctor for "vomiting 2 or more times," and more generally whenever fever comes with "repeated vomiting or diarrhea" at any age.

The NHS's fever page doesn't single out vomiting as its own 999-level trigger, but its general guidance still applies: if you're worried, or your baby seems increasingly unwell, dehydrated (few wet nappies, sunken eyes, no tears when crying), or won't feed, contact your doctor or NHS 111 rather than waiting it out.

Can my baby sleep with a fever, or should I wake them to check?

Official guidance doesn't set a temperature-based sleep cutoff — none of the NHS or AAP pages frame the question this way, so there's no sourced number for "too hot to sleep."

Instead, both bodies focus on the red-flag signs above (breathing, responsiveness, rash, hydration, the age-based call thresholds). If your baby is sleeping peacefully and isn't showing any of those signs, letting them rest is reasonable; if you're checking a red flag, wake them rather than waiting for morning.

Review the red-flag signs →