Fever in Babies and Newborns

Chris Yun, M.D.by Chris Yun, M.D.
Fever in Babies and Newborns

Fever in Babies and Newborns

No one wants to see their baby or newborn with a fever. As we all know, your baby can’t just tell you what’s wrong!

As a parent or caregiver, it’s crucial to understand the common causes of fevers, their presentation, and their potential risks. Not all fevers are something to worry about, but you should never ignore them.

Recognizing the signs of a fever and knowing when to consult a healthcare provider ensures the best possible care for your baby.

Here is our guide to fevers in babies and newborns.

What causes fevers in infants?

Let’s take a look at the leading causes of fever in infants. Generally speaking, fevers are a natural immune response to combat infections.They occur when the body's internal temperature regulation system rises to help fight against infection. They have many possible causes.


Infections are the most common cause of fever in infants. These are usually viral and more rarely bacterial or fungal.

Examples of infections that can cause fevers in infants include colds and flus, ear infections, and stomach bugs. In rarer cases, fever may indicate bacterial infections like urinary tract infections, meningitis, pneumonia, or sepsis.


It’s not uncommon for babies to develop a low-grade fever after receiving vaccinations.

This is a normal immune response to the vaccine, and the fever usually subsides within 24 to 48 hours.


Babies and newborns can’t regulate their temperature efficiently and are vulnerable to overheating. Overdressing or exposing an infant to hot weather can cause overheating. 

Avoid having your baby outside for prolonged periods of time if the heat index if 90F or above. Between 75 and 90F, make sure to keep your baby in shade and in light, breathable clothing.


Teething might cause a mild increase in body temperature, although it is generally not considered a true fever. The discomfort and inflammation associated with teething can lead to a slightly elevated temperature in some babies.

Other medical conditions

Although less common, rare medical conditions can cause fevers in infants.

These may include autoimmune or inflammatory conditions, metabolic disorders, or certain medications.

Indications your infant might have a fever

Recognizing a baby's fever isn’t always straightforward, especially in mild cases. 

Here are the most important signs to look out for:

  1. Warm forehead: A warm forehead is one of the most straightforward signs of a fever. Parents can gently place the back of their hand on the baby's forehead to assess if it feels warmer than usual. However, confirming a fever using a thermometer is essential, as a warm forehead alone isn’t enough to accurately determine if your child has a fever.

  2. Changes in body temperature: Similarly, fever might cause a baby’s temperature to fluctuate. Your baby might feel hot and sweaty one moment and then cool and clammy the next.

  3. Fussiness, disinterest, lethargy, or irritability: Babies with a fever often become fussy or irritable, crying or wriggling more frequently than usual. They might be disinterested in play and interaction or tired with low energy.

  4. Poor appetite: Babies with fevers often exhibit a decreased appetite, refusing to nurse or take a bottle.

  5. Difficulty sleeping: Fevers can disrupt a baby's sleep patterns. A feverish baby may be restless, wake up frequently, or have trouble sleeping.

  6. Chills or shivering: While less common in infants, chills or shivering may indicate that the baby's body is attempting to raise its temperature to fight off an infection. This often precedes the onset of a fever.

  7. Dehydration: Fevers can cause increased fluid loss, potentially leading to dehydration. Signs of dehydration in infants include fewer wet diapers, sunken eyes, a dry mouth, and decreased tears when crying.

How to take your baby's temperature

Taking a baby’s temperature is a slightly different procedure for a young child, adolescent, or adult.

For children under 3 months old, you should use a rectal thermometer if possible. A forehead thermometer is an effective alternative. Here’s the procedure as recommended by authorities such as Stanford Health and Hopkins Medicine:

First, prepare the thermometer by cleaning it with soap and water, then apply a lubricant, such as petroleum jelly, to the tip.

Place your baby on a clean, flat surface, either lying on their back with their legs bent towards their chest or on their stomach with their legs hanging down.

Gently insert the lubricated tip of the digital thermometer about half an inch into the baby's rectum. Hold the thermometer in place, keeping your baby still and comfortable until the thermometer beeps. After taking the temperature, clean and sanitize the thermometer.

For babies aged between 3 months and 3 years, Healthline indicates it’s possible to use either a rectal thermometer, axillary thermometer (under the armpit), or temporal artery thermometer (forehead). A temporal artery (forehead) thermometer is perhaps the simplest to use, and studies indicate it’s virtually as effective as a rectal thermometer.

To use a temporal artery thermometer, place it on the center of your baby's forehead. Then, following the manufacturer's instructions, gently slide the thermometer across the forehead towards the hairline.

Ear thermometers aren’t recommended for infants under three months due to their narrow ear canals.

What temperature is considered a fever in a baby?

So, how do you interpret your baby’s thermometer reading? In babies, the threshold for fever varies depending on their age. Here are the general guidelines as indicated by professional medical organizations:

  • Infants under 3 months: A temperature of 100.4°F (38°C) or higher is considered a fever.

  • Babies 3 to 6 months: A temperature of 101°F (38.3°C) or higher is considered a fever.

  • Babies over 6 months: A rectal temperature of 103°F (39.4°C) or higher is considered a fever.

Bear in mind that rectal temperatures are typically higher than oral, axillary, or temporal artery temperatures. Once you have the reading, consult the guidelines for your child’s age and the thermometer you used.

What to do if your baby has a fever

When should I worry about my baby's fever?

While most fevers in babies are a natural response to minor infections or illnesses, keeping a close eye on developments is crucial. Here are four factors to watch out for:

  1. Your baby’s age: Any fever in a baby less than 3 months old should be evaluated by your pediatrician, and if your baby is less than 1 month old, they must be evaluated in an emergency room for testing.

  2. Duration: If your baby's fever persists for more than 48 to 72 hours without any signs of improvement, contact your pediatrician.

  3. Accompanying symptoms: If your baby's fever is accompanied by symptoms such as difficulty breathing, a rash, severe vomiting or diarrhea, or signs of dehydration, consult a healthcare provider immediately.

  4. Unresponsiveness or lethargy: If your baby is difficult to wake, appears listless, or shows a significant decrease in energy levels, contact a physician as soon as possible.

  5. Seizures: Febrile seizures, which are seizures triggered by a fever, can occur in children aged between 6 months to 6 years. These can be alarming for parents but they are generally harmless in the long term. However, it’s still essential to consult a healthcare provider if your baby experiences one.

How do I bring my baby's fever down?

If your baby has a minor fever with no other worrying symptoms, or you suspect it’s associated with overheating or a vaccination, you can attempt to bring your baby’s temperature down.

For babies over two months old, acetaminophen can be given to help reduce fever. Ibuprofen is also an option for babies over six months old.

According to WebMD, the advised dosage for liquid acetaminophen is as follows:

  • 6 to 11 lbs: 1.25 ml or 1/4 tsp

  • 12 to 17 lbs: 2.5 ml or 1/2 tsp

  • 18 to 23 lbs: 3.75 ml or 3/4 tsp

  • 24 to 35 lbs: 5 ml or 1 tsp

  • 36 to 47 lbs: 7.5 ml or 1.5 tsp

  • 48 to 59 lbs: 10 ml or 2 tsp

  • 60 to 71 lbs: 12.5 ml or 2.5 tsp

  • 72 to 95 lbs: 15 ml or 3 tsp

  • 96 lbs and above: 20 ml or 4 tsp


Follow dosage guidelines rigidly based on your baby's age and weight.

If you feel the weather or heat has caused or exacerbated your baby’s temperature, dress your baby in light clothing to avoid overheating. Opt for lightweight, breathable clothing that allows for proper heat dissipation. Maintain a comfortable room temperature, ideally between 68 to 72°F (20 to 22°C).

Offer cool fluids to your baby to keep them hydrated. Encourage frequent nursing or bottle-feeding, and for babies over six months old, offer small amounts of water to help keep them cool and hydrated.

You can also use a lukewarm sponge to decrease your baby's body temperature. Gently sponge your baby with lukewarm water. Avoid cold water, as this can cause shivering.

Make sure your baby gets plenty of rest to aid in their recovery. If your baby has trouble sleeping due to discomfort, consult your healthcare provider about possible solutions. During this time, monitor your baby's temperature regularly to ensure it remains stable or comes down.

Last but never least, provide comfort and support by holding, cuddling, and soothing your little one. If your baby's fever doesn’t respond or other symptoms appear, consult your baby's healthcare provider.

When to call your baby's healthcare provider

Rest assured, most fevers respond well to intervention and come down on their own.

If your baby’s temperature doesn’t change for over 48 hours or other issues develop, as listed above, consider calling your baby’s healthcare provider.


Here’s a recap:

  1. Fevers in babies less than 3 months old: Contact your pediatrician right away. If your baby is less than 1 month old, go to the emergency room.

  2. Persistent fever: If the fever lasts more than 48 to 72 hours without any signs of improvement, your baby may need professional medical attention.

  3. Worsening symptoms: If the fever is accompanied by symptoms that worsen over time or don’t improve, such as difficulty breathing, severe vomiting, diarrhea, or signs of dehydration, call your healthcare provider.

  4. Unresponsiveness or lethargy: If your baby appears listless, difficult to rouse, or shows a significant decrease in activity levels, it’s wise to inform your healthcare provider.

  5. Seizures: If your baby experiences a seizure, even if it is believed to be a febrile seizure, contact your healthcare provider.

  6. Inconsolable crying: Contact a healthcare provider if your baby is in apparent pain or discomfort and can’t be soothed.

  7. After vaccinations: Contact your health provider if your baby develops a fever following vaccinations and the fever persists beyond 48 hours or is accompanied by other concerning symptoms.

What to do next

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We provide comprehensive pediatric care for babies and infants of any age. With exceptional hospitality, modern technology, and transparent pricing, Juno offers complete healthcare solutions for parents and children.

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