How Do I Take My Baby's Temperature Correctly?
The short answer
Rectal temperature is the gold standard for babies under 3 months and the most accurate method for all infants. A rectal temperature of 100.4°F (38°C) or higher is considered a fever. Temporal artery (forehead) and tympanic (ear) thermometers can be used in older babies but are less accurate in very young infants.
Parents everywhere have the same worry. You are doing the right thing by looking into it.
By Age
What to expect by age
Rectal temperature is the only recommended method for babies under 3 months because accuracy is critical at this age. A fever of 100.4°F (38°C) or higher in a newborn requires immediate medical evaluation. Use a digital rectal thermometer with petroleum jelly on the tip, insert gently about half an inch, and hold in place until it beeps. Never use a glass mercury thermometer.
Rectal temperature remains the most accurate method, though temporal artery (forehead) thermometers can be used as a screening tool. If a forehead reading suggests fever, confirm with a rectal temperature. Axillary (underarm) temperature can screen but may read 1-2 degrees lower than actual core temperature. Always report the method used when calling your pediatrician.
You can now use temporal artery, tympanic (ear), or rectal thermometers. Ear thermometers are generally reliable after 6 months but can give inaccurate readings if there is earwax buildup or an ear infection. Forehead thermometers are convenient and reasonably accurate for this age. For the most precise reading, rectal remains best.
Multiple methods work well at this age. Many parents prefer temporal artery thermometers for convenience and less distress. Ear thermometers are also reliable. Rectal is still the most accurate but may be harder with an active toddler. Oral thermometers are not yet recommended as toddlers cannot hold them properly under their tongue.
Temporal artery and ear thermometers work well for toddlers. Some children this age may begin to cooperate with oral thermometers, but most do better with forehead or ear readings. Consistent use of the same method helps you track temperature trends. Always tell your doctor which method you used when reporting a temperature.
What Should You Do?
When to take action
- A slight temperature variation of 0.5-1°F throughout the day, with higher readings in the late afternoon
- Temperature readings differ slightly between methods (underarm may read lower, rectal may read slightly higher)
- A brief temperature rise after bundling, physical activity, or a warm bath
- Your baby feels warm but the thermometer reads below 100.4°F rectally
- You are unsure which thermometer method is best for your baby's age
- Your thermometer gives inconsistent readings and you want guidance on technique
- Your baby's temperature seems elevated but you are not sure if it is accurate
- Any rectal temperature of 100.4°F (38°C) or higher in a baby under 3 months old requires immediate medical evaluation
- A temperature of 104°F (40°C) or higher at any age, or any fever with lethargy, rash, difficulty breathing, or refusal to feed
Sources
Related Resources
Trust your instincts. If something feels wrong, reach out to your pediatrician.
Worrying about your baby means you care. That is a good thing.
Related Medical Concerns
Should I Give Acetaminophen or Ibuprofen for Fever?
Acetaminophen (Tylenol) can be used from birth (with doctor guidance for babies under 3 months), while ibuprofen (Motrin/Advil) is only safe after 6 months of age. Both are effective fever reducers. Acetaminophen works for about 4-6 hours and ibuprofen for 6-8 hours. Always dose by weight, not age, and use the measuring device that comes with the medicine.
Baby Has a High Fever Over 104 Degrees F
A fever above 104 degrees F (40 degrees C) in a baby or toddler can be alarming, but the height of the fever alone does not necessarily indicate a more serious illness. Many common childhood viral infections (like roseola) can cause high fevers. What matters more than the number is how your child looks and behaves. A child with a 104 degree F fever who is still alert, making eye contact, and drinking fluids is less concerning than a child with a 102 degree F fever who is limp and unresponsive. However, fevers above 104 degrees F should always be discussed with your pediatrician.
Managing Fever Without Medication
Fever is the body's natural defense against infection, and not every fever needs medication. For babies over 3 months with low-grade fevers who are otherwise comfortable, non-medication strategies like keeping them lightly dressed, offering extra fluids, and maintaining a comfortable room temperature can be effective. The goal of fever management is comfort, not achieving a specific number on the thermometer.
My Baby's Head Shape Looks Abnormal
Many babies develop temporary head shape irregularities that are completely normal. A cone-shaped head from vaginal delivery reshapes within days. Mild positional flattening (plagiocephaly) from sleeping on the back is very common and usually improves with repositioning and tummy time. However, head shape changes involving ridges, a persistently bulging fontanelle, or rapid head growth changes should be evaluated to rule out craniosynostosis.
Achondroplasia (Dwarfism) in Babies
Achondroplasia is the most common form of short-limbed dwarfism, affecting about 1 in 15,000 to 40,000 births. It is caused by a mutation in the FGFR3 gene and is usually apparent at birth with characteristic features including short limbs, a larger head, and a prominent forehead. Intelligence is normal. With monitoring for specific complications and supportive care, children with achondroplasia lead full, active, and independent lives.
Adenoid Hypertrophy and Breathing
Adenoids are lymphoid tissue located behind the nose that help fight infection in young children. When adenoids become enlarged (adenoid hypertrophy), they can block the nasal airway, causing chronic mouth breathing, snoring, nasal speech, and sleep-disordered breathing. Enlarged adenoids are most common between ages 2-7 and are a leading cause of obstructive sleep apnea in young children. Treatment ranges from watchful waiting and nasal steroids to surgical removal (adenoidectomy) if breathing or sleep is significantly affected.