Quick Answer
Use a digital thermometer appropriate for your baby's age and follow its instructions. Touching the forehead cannot reliably tell you whether a baby has a fever. For young infants, a rectal reading is generally the most accurate; ask your pediatrician to show you the technique if you are unsure.
A baby younger than 3 months with a temperature of 100.4°F (38°C) or higher needs immediate medical assessment, even if they seem comfortable. Call your pediatrician urgently; if you cannot reach them promptly, seek urgent in-person care. Do not delay care to repeat a reading or try fever medicine first.
Which Thermometer Should I Choose?
A digital thermometer is a useful home essential. Check the age range and measurement site specified by the manufacturer.
Underarm readings are convenient but less accurate and can miss fever. Forehead devices vary in their approved ages and technique. Ear thermometers are not reliable for babies younger than 6 months. Oral measurements are not suitable for babies.
Avoid mercury thermometers, forehead fever strips, and relying on a pacifier thermometer to rule out fever in a young infant. Keep thermometers and batteries out of children's reach.
How Do I Take a Rectal Temperature Safely?
Ask your clinician first if your baby has a medical condition or has been told to avoid rectal measurements. If you are uncomfortable or unsure, contact the pediatrician for help rather than improvising.
- Wash your hands and clean a digital thermometer as directed.
- Use a thermometer intended for rectal use and label it so it is not used in the mouth.
- Apply a small amount of suitable lubricant to the tip as instructed.
- Position your baby securely, supporting them throughout.
- Insert only the short distance specified for your baby's age by the device instructions or clinician. Never force it; stop if you meet resistance.
- Hold the thermometer and your baby still until the reading is complete, then remove and clean it.
Never leave a baby alone with a thermometer in place. Stop and seek advice if there is pain, bleeding, or difficulty. A diaper-changing surface requires continuous hands-on supervision.
How Do I Take an Underarm Reading?
Place the tip against dry skin in the centre of the armpit and hold the arm gently against the body until the device finishes, following its instructions.
Tell the clinician that the measurement was underarm. Do not add or subtract a fixed number to convert it to a rectal temperature; the difference is not reliably predictable.
A normal underarm result does not rule out fever or serious illness. If your young baby seems unwell or feels unusually hot or cold, seek advice rather than relying on a reassuring number.
What About Forehead Thermometers?
Use only a device suitable for your baby's age and follow its positioning instructions. Sweat, head coverings, environmental temperature, and incorrect distance can affect some readings.
If the result does not fit how your baby looks, contact your pediatrician about the appropriate next step. Do not spend time comparing multiple devices when urgent symptoms are present.
What Should I Tell the Pediatrician?
Report your baby's exact age, the temperature, whether it was Fahrenheit or Celsius, the measurement site, and when it was taken. Include feeding, wet diapers, breathing, alertness, other symptoms, and any medicine given.
Keep the actual reading rather than reporting only "a high fever." Mention prematurity, immune problems, or a medical care plan, because these can change the response needed.
When Should I Call for an Older Baby?
Babies aged 3 to 6 months should receive prompt medical advice for fever, particularly if feeding poorly, uncomfortable, or less alert. Ask your pediatrician for the temperature and symptom thresholds they want you to use.
For older babies, how they breathe, drink, respond, and pass urine matters alongside the number. Call for persistent or recurring fever, worsening symptoms, reduced intake, or any concern that your baby is not behaving normally.
A temperature around 104°F (40°C) or higher warrants prompt medical advice at any infant age. Do not wait for a high number if your baby looks seriously unwell.
Can a Low Temperature Be Concerning?
Yes. Newborns can be seriously ill without fever, and an unusually low temperature can also be a warning sign. Contact your pediatrician urgently if a newborn has a low reading, especially with poor feeding, reduced activity, or difficulty maintaining warmth.
Keep your baby appropriately warm, but do not use heating pads, hot-water bottles, or direct heat to correct the reading. Seek assessment rather than repeatedly warming and rechecking an unwell baby.
Should I Give Fever Medicine?
For a baby younger than 3 months with fever, seek medical advice before giving medicine unless the clinical team has provided a specific plan. A lower reading after medicine does not rule out serious illness.
For older babies, ask about an appropriate medicine and weight-based dose. Do not give ibuprofen to a baby younger than 6 months unless directed by a clinician, and never give aspirin to a child unless specifically prescribed.
Do not alternate medicines without a clear plan or use adult preparations. Avoid cold baths, ice, and alcohol rubs. Offer usual milk feeds and comfortable clothing, following any medical restrictions.
What Parents Can Try
- Keep an appropriate digital thermometer accessible to adults.
- Learn the technique before your baby becomes ill.
- Record the reading, units, method, and time.
- Watch feeding, wet diapers, breathing, and responsiveness.
- Keep the pediatrician's daytime and out-of-hours contact details available.
- Seek help promptly rather than waiting for the number to rise.
When Should I Seek Emergency Help?
Call emergency services for breathing difficulty, blue or grey colouring, collapse, seizures, or a baby who is very difficult to wake. A new rash that does not fade when pressed, especially with an unwell baby, also needs emergency assessment.
Do not delay emergency care to take a temperature. Poor feeding, substantially fewer wet diapers, repeated vomiting, marked lethargy, or unusual inconsolable crying needs prompt medical advice even without fever.
Remember: fever of 100.4°F (38°C) or higher in a baby younger than 3 months requires immediate medical assessment, including after vaccination unless your baby's clinician has given you specific instructions. Do not assume it is teething.
Key Takeaway
Use an age-appropriate digital thermometer and report the exact reading and method without converting between sites. Young-infant fever needs immediate assessment, while breathing, hydration, and responsiveness matter at every age. A normal temperature cannot rule out serious illness.
Parents Also Ask
How Do I Know If My Baby Is Dehydrated?
How Do I Feed My Baby When They Have a Cold?
What Should I Ask at My Baby's Well-Child Visit?
This article is for informational purposes only and is not a substitute for professional medical advice, diagnosis, or treatment. Always consult your pediatrician or a qualified healthcare provider with questions about your baby's health.