Fever In Newborns: What's Normal And What's Not?

Fever in newborns is a common concern for new parents. While fever is a normal response to infection in adults, only about half of newborns with an infection have a fever. In some cases, newborns may have a lowered body temperature when infected. A newborn's temperature regulation system is not fully developed, and they lack the insulating fat layer of older babies and children. This means they can also develop a fever due to overheating or dehydration. If your baby is younger than 3 months old and has a rectal temperature of 100.4°F (38°C) or higher, seek immediate medical attention.

What temperature constitutes a fever in newborns?

A newborn baby's body temperature is controlled by a system that is not yet fully developed. This means that a newborn can have a low body temperature even when they have an infection. They may also experience changes in activity, feeding, or skin colour.

A newborn baby's average body temperature is 98.6 °F. A fever is a rectal temperature of 100.4 °F or higher, or an armpit temperature of 99 °F or higher. If your baby is younger than 3 months old and has a rectal or forehead temperature of 100.4 °F or higher, call your baby's healthcare provider immediately. This is an emergency and you will need to take your baby to the closest emergency room for assessment.

If your baby is between 2 and 3 months old and their temperature (taken any way) is greater than 100.4 °F, call your baby's primary care provider immediately. If your newborn is younger than 2 months and has a fever, go to an emergency department immediately.

If your baby is older than 3 months, call the primary care provider right away if you notice any of the following symptoms:

• Your child is crying inconsolably.
• Your child is difficult to awaken.
• Your child has been in a very hot place, such as inside a hot car.
• Your child has other symptoms such as a severe headache, stiff neck, or other severe pain.
• Fever is accompanied by a rash.
• Your child looks or acts very sick.
• Your child has severe vomiting or diarrhoea.
• Your child is not up to date on their vaccines.
• Your child has a seizure (convulsion).

What to do if your newborn has a fever

A fever in newborns can be scary, but it's important to remember that it is usually not a cause for concern and is one of the most common issues new parents face. A fever is often a sign that your baby's body is fighting off an illness or infection, and their immune system is working harder to get rid of germs.

However, if your newborn has a fever, there are some important steps you should take to ensure their safety and well-being:

Monitor their temperature:

• Take your baby's temperature using a digital thermometer. The rectal temperature (taken through the anus) is the most accurate method for young children, but you can also take their armpit or forehead temperature.
• A baby's normal temperature averages 98.6°F (37°C). A fever is typically defined as a rectal temperature of 100.4°F (38°C) or higher, or an armpit temperature of 99°F (37.2°C) or higher.
• If your baby is younger than 2 months old with a rectal temperature of 100.4°F (38°C) or higher, go to the emergency department immediately.
• If your baby is between 2 and 3 months old with a fever, call your baby's doctor right away.

Keep them comfortable:

• Dress your baby in lightweight and comfortable clothing. Avoid bundling them up with too many layers or blankets, as this can increase their body temperature.
• Maintain a comfortable room temperature, ideally between 72°F and 75°F (22°C and 24°C).
• Ensure your baby stays hydrated by offering them breast milk or formula frequently. If they are older than 6 months, you can also offer them Pedialyte or other electrolyte drinks.

Treat the fever:

• Bathe your baby in lukewarm water to help bring down their body temperature. Avoid cold water or alcohol baths, as they can cause shivering and actually increase body temperature.
• You can give your baby acetaminophen (Tylenol) or ibuprofen (Advil, Motrin) to help reduce their fever, but always consult with your doctor first, especially if your baby is younger than 3 months old.
• Never give aspirin to a baby, as it has been linked to Reye's syndrome, a rare but potentially serious illness.

Watch for other symptoms:

• Fever is often accompanied by other symptoms such as crankiness, fussiness, less activity, warm and flushed skin, rapid heart rate, and rapid breathing.
• If your baby displays any of the following symptoms, seek medical attention: lethargy or unresponsiveness, difficulty breathing or eating, uncontrollable crying, dehydration, severe headache or pain, recent exposure to a very hot place, seizures, vomiting, rash, stiff neck, or other concerning symptoms.

Remember, while fever is often a normal response to an infection, a fever in newborns can sometimes indicate a more serious condition. Always trust your instincts and seek medical advice if you are concerned about your baby's health.

How to take your newborn's temperature

A newborn baby's temperature should be taken with a digital thermometer. Do not use a mercury thermometer, as these pose a risk of poisoning if they break.

There are several places on the body where you can take a newborn's temperature. These include:

Rectal (in the bottom). This is the most accurate method, especially for babies younger than 3 months old. To take a rectal temperature, follow these steps:

• Purchase a digital rectal thermometer from a drugstore.
• Wash the thermometer with soap and water or disinfecting alcohol before and after each use.
• Apply a thick layer of petroleum jelly to the end of the thermometer that will be inserted.
• Place your baby on their stomach or hold their legs up near their ears while they lie on their back.
• Stabilize your baby with one hand on their back or by holding their feet firmly to prevent them from moving too much.
• Slowly insert the thermometer about half an inch into the anus, so that only the metal bulb is inside.
• Gently hold the thermometer steady between your index and forefinger.
• Wait for the thermometer to beep, then remove it gently.

Under the arm (axillary). This is the least reliable method but can be used as an initial check for a child of any age. A disc-shaped thermometer is the most comfortable for this method. To take an axillary temperature:

• Place the tip of the thermometer in your baby's armpit, ensuring that the armpit is dry.
• Close the armpit by holding the elbow against the chest until the thermometer beeps (usually about 10 seconds). Ensure that the tip of the thermometer remains covered by skin.
• Your baby has a fever if the temperature is 99.0°F (37.2°C) or higher. If you are unsure, take their temperature by rectum or forehead.

Forehead (temporal). This method can be used for children aged 3 months and older. It is also suitable for a first pass if a child under 3 months old shows signs of illness. To take a forehead temperature:

• Place the sensor head of the thermometer at the center of the forehead, touching the skin.
• Slowly slide the thermometer across the forehead toward the top of the ear, keeping it in contact with the skin.
• Stop when you reach the hairline and read the temperature on the display screen.

Ear (tympanic). Ear thermometers are quick and can be used for babies older than 6 months. However, they may not be accurate for newborns and older infants. To take an ear temperature:

• Pull the ear gently backward and up if the child is over 1 year old.
• Aim the tip of the ear probe between the opposite eye and ear.
• Note that earwax, ear infections, and ear tubes may interfere with accurate readings.

Mouth (oral). This method is not recommended for children under 4 years old, as it can be difficult for younger children.

It is important to remember that a fever is not an illness but a symptom of one. Most fevers in newborns are caused by viral infections, while bacterial infections are less common. If your newborn has a fever, contact your healthcare provider for advice and guidance.

How common is fever in newborns?

Fever in newborns is relatively common, but it is important to monitor and address it promptly as it can be a sign of a dangerous infection. Newborns have an immature temperature regulation system, so they may not develop a fever when fighting an infection or illness, but they can also develop a fever due to other causes that may be more serious.

A newborn's body temperature is regulated differently from an adult's. Adults have a tightly controlled internal thermostat that helps regulate body temperature through shivering and sweating. In contrast, newborns lack this well-developed thermostat and the insulating fat layer that older babies and children have. As a result, their body temperature can fluctuate more easily, and they are more susceptible to temperature extremes.

Fever in newborns may be caused by various factors, including infection, overheating, low fluid intake or dehydration, and, in rare cases, more serious conditions such as bacterial meningitis. Only about half of newborns with an infection will develop a fever, and some, especially premature babies, may exhibit a lowered body temperature along with other signs of infection, such as changes in behaviour, feeding, or skin colour.

To prevent overheating, it is important to maintain a comfortable room temperature of around 72 to 75 degrees Fahrenheit and dress your baby according to your own comfort level at that temperature. Avoid bundling them in too many layers or blankets, and never leave them alone in a closed car, even for a short period, as their temperature can rise rapidly, leading to heat stroke and potentially fatal consequences.

Dehydration is another concern, as some newborns may not take in enough fluids, causing a rise in body temperature. This is particularly important to monitor during the second or third day after birth. If adequate fluid intake is not maintained, dehydration can occur, requiring intravenous (IV) fluids for treatment.

If your baby is younger than 2 to 3 months old and has a rectal temperature of 100.4 degrees Fahrenheit (38 degrees Celsius) or higher, it is considered an emergency, and you should seek immediate medical attention. For older infants and young children, a fever is typically defined as a rectal temperature of 101 degrees Fahrenheit or higher, and a call to the doctor is recommended.

What are the causes of fever in newborns?

A newborn baby's body temperature regulation system is not well developed. Therefore, a fever in newborns may or may not occur with an infection or illness. However, fever in babies can be due to other causes that may be even more serious. Here are some common causes of fever in newborns:

Infection

Fevers are a normal response to infection in adults, but only about half of newborns with an infection have a fever. Some, especially premature babies, may have a lowered body temperature with an infection or other signs such as a change in behaviour, feeding, or colour. Most fevers in children are caused by viral infections, while a smaller number are due to bacterial infections, such as ear infections, strep throat, or pneumonia.

Overheating

While it is important to keep a baby from becoming chilled, a baby can also become overheated with many layers of clothing and blankets. This can occur at home, near heaters or heat vents, or in a hot car. An overheated baby may have a hot, red, or flushed face and may be restless.

Low fluid intake or dehydration

Some babies may not take in enough fluids, which causes a rise in body temperature. This may happen around the second or third day after birth. If fluids are not replaced with increased feedings, dehydration can develop and cause serious complications.

Underlying chronic disease

Prolonged fever, or fever recurring over a week, can be a sign of underlying chronic disease.

Bacterial meningitis

In extremely rare cases, fever can signal a life-threatening disease called bacterial meningitis. If your infant has a fever greater than 101 degrees Fahrenheit and is lethargic or you can't wake them up normally, seek emergency medical attention.

Frequently asked questions