Treatment of Fever in a Newborn: What Parents Should Do at 100.4°F (38°C)

A warm newborn can make any parent worry.

The first question is simple.

Is it really a fever?

For a young baby, that number matters. A rectal temperature of 100.4°F (38°C or higher is a fever.

And there is one rule I want every parent to remember.

Do this even if your baby is feeding, sleeping, and otherwise looks well.

The treatment of fever in a newborn is different from fever care in an older baby or child. The goal is not to cool the baby at home. The first goal is to make sure a serious infection is not being missed.

I am a parent and grandparent, not a doctor. Over many years of family life, one lesson has stayed with me. With a very young baby, it is better to ask for medical help early than to guess at home.

What Counts as a Fever in a Newborn?

A fever is not just warm skin.

You need a thermometer.

For a young infant, a temperature of 100.4°F or 38°C or higher is considered a fever.

A digital rectal thermometer gives the most reliable reading for babies, especially babies younger than 3 months.

Feeling the forehead is not accurate enough.

Fever strips are also not reliable enough for this decision.

Ear thermometers are not recommended for very young babies because their ear canals are too small to give dependable readings.

Newborn Does Not Mean the Same as Under 3 Months

There is an important point here.

Doctors usually use the word newborn for the first 28 days of life.

But the fever safety rule does not stop at day 28.

If your baby is 3 months old or younger and has a rectal temperature of 100.4°F or 38°C or higher, call your pediatrician immediately.

This includes:

• A 2 week old baby
• A 5 week old baby
• A 2 month old baby
• A baby who has not yet reached 3 months

This is one of the most important facts about fever in babies under 3 months.

Why Fever in a Young Baby Needs Fast Medical Care

Fever itself is a sign.

It tells us that something may be happening in the body.

Many fevers come from common infections.

But in a very young baby, doctors also need to think about infections that can become serious quickly.

Possible causes can include:

• Viral infections
• Urinary tract infections
• Respiratory infections
• Blood infections
• Meningitis
• Other bacterial infections

A parent cannot tell the cause from the temperature number alone.

A baby may even look fairly well at first.

That is why the safest response to newborn fever is medical evaluation rather than home treatment.

What to Do if Your Baby Has a Fever

If your baby is 3 months old or younger and the rectal temperature reaches 100.4°F or 38°C, follow these steps.

1. Call Your Pediatrician Immediately

Do not wait to see if the temperature rises.

Do not wait until morning just because the baby seems comfortable.

Tell the doctor:

• Your baby's exact age
• The temperature
• How you measured it
• When you measured it
• How the baby is feeding
• How the baby is breathing
• How many wet diapers you have seen
• Any vomiting, diarrhea, rash, cough, or unusual behavior
• Any recent vaccines

Your pediatrician can tell you where your baby should be evaluated.

2. Do Not Try to Bring the Fever Down Before Calling

The temperature is useful information for the doctor.

Do not focus on making the number lower before you seek advice.

For a baby this young, finding the cause matters more than trying to lower the temperature at home.

3. Keep Feeding Normally if Your Baby Can Feed

Offer breast milk or formula as usual while you arrange medical care.

Do not give plain water to a newborn for fever.

Do not force a baby who is struggling to feed.

Poor feeding itself is important information to tell the doctor.

4. Keep Your Baby Comfortable

Do not bundle a feverish baby in many layers.

Normal comfortable clothing is enough.

You do not need to set the room to one exact temperature.

The goal is simple.

Keep the room comfortable and avoid overheating.

Do Not Use a Fixed Room Temperature as Fever Treatment

You may see advice online telling parents to keep a baby's room at one exact number during a fever.

That is not the main treatment for infant fever.

A young baby's fever may be a sign of infection.

Changing the thermostat does not treat that cause.

Avoid heavy blankets or too many clothes, but do not try to make your baby cold.

Should You Give Acetaminophen to a Newborn With Fever?

Do not give fever medicine to a baby under 3 months before speaking with a healthcare professional.

A fever during the first 12 weeks needs medical evaluation.

Your doctor may give you specific instructions after evaluating your baby's age, weight, temperature, symptoms, and medical history.

Do not guess the dose.

Do not use a kitchen spoon to measure medicine.

Do not give medicine just because the bottle says it is made for infants.

Can a Baby Under 6 Months Take Ibuprofen?

Ibuprofen should not be given to a baby younger than 6 months unless the baby's doctor specifically tells you to use it.

For a newborn or young infant with fever, call the doctor first.

Never Give Aspirin to a Baby

Do not give aspirin to a baby or child for fever unless a specialist has prescribed it for a specific medical reason.

For normal fever care, aspirin is not a medicine parents should give children.

Should You Give a Newborn a Cold Bath?

No.

Do not use:

• Ice
• Very cold water
• Alcohol rubs
• Cold packs
• Home remedies meant to force the temperature down

These actions do not treat the cause of the fever.

Some can make the baby uncomfortable or unsafe.

Call your pediatrician instead.

How to Check a Newborn's Temperature

A baby temperature should be measured with a digital thermometer.

For infants under 3 months, the American Academy of Pediatrics considers a rectal reading the most reliable and accurate.

Use a clean digital thermometer that is meant for rectal use.

Follow the thermometer instructions carefully.

If you have never taken a rectal temperature and do not feel comfortable doing it, ask your pediatrician or nurse to show you the safe method.

Do Not Depend on Touch Alone

A baby's skin can feel warm for many reasons.

The baby may have been:

• Wrapped in a blanket
• Held against your body
• Crying
• In a warm room

Touch can tell you to check.

It cannot confirm a fever.

Signs That Need Emergency Care

A fever in a baby under 3 months already needs prompt medical contact.

Some symptoms make the situation even more urgent.

Call emergency services or seek emergency care if your baby:

• Has trouble breathing
• Is struggling for each breath
• Has blue or gray lips, tongue, or skin
• Cannot be awakened normally
• Is extremely weak or unresponsive
• Has a seizure
• Has a purple or bruise like rash that appears suddenly
• Has repeated vomiting and cannot feed
• Looks severely ill

These are important signs of serious illness.

What if the Baby Has a Fever but Looks Fine?

Still call.

This is where young babies are different from older children.

A baby who is 3 months old or younger may need evaluation even when they:

• Are awake
• Are feeding
• Are not crying much
• Do not have a rash
• Do not have a cough

A rectal temperature of 100.4°F or 38°C or higher is enough reason to contact your pediatrician immediately.

What if the Fever Happens After Vaccines?

Some babies can develop a temperature after vaccination.

But age still matters.

If a baby is in the first 12 weeks of life and has a fever, contact your pediatrician.

Tell the doctor which vaccine was given and when.

Your doctor can decide whether the temperature is likely linked to the vaccine or whether your baby needs further evaluation.

Do not automatically give medicine before asking for advice.

Can Overheating Cause a High Temperature?

Too many clothes or blankets can make a baby warm.

But do not assume that a measured temperature of 100.4°F or 38°C in a young infant is just from a warm room.

Remove extra layers and contact your pediatrician if your baby meets the fever threshold.

It is safer to let a healthcare professional decide what comes next.

Can Dehydration Cause Fever in a Newborn?

Dehydration can happen when a sick baby is feeding poorly or losing fluid.

Parents should not assume dehydration is the simple cause of a fever.

Watch for:

• Much less feeding
• Fewer wet diapers
• Dry mouth
• Unusual sleepiness
• Weakness

Tell your doctor about these changes.

What Doctors May Do for a Young Baby With Fever

The medical team will first look at your baby carefully.

They will ask about:

• Your baby's age
• The temperature
• Feeding
• Wet diapers
• Birth history
• Recent illness
• Vaccines
• Exposure to sick people

Depending on the baby's age and examination, doctors may test urine or blood.

Some babies may need other tests.

In some cases, doctors may test spinal fluid.

Not every baby gets every test.

The plan depends on the baby's exact age, how the baby looks, test results, and other risk factors.

Does Every Newborn With Fever Need Antibiotics?

No.

Antibiotics treat bacterial infections.

They do not treat viruses.

A doctor decides whether antibiotics are needed after evaluating the baby.

Never give leftover antibiotics to a baby.

Never use another person's medicine.

Why You Should Not Wait for the Fever to Reach 102°F

For an older child, parents may sometimes watch a mild fever at home.

A young infant is different.

The important number is not 102°F.

It is 100.4°F or 38°C.

If the baby is 3 months old or younger, call your pediatrician at that point.

What About a Temperature Below 100.4°F?

A number below 100.4°F does not meet the usual fever definition.

But the number is not the only thing that matters.

Contact a doctor if your baby:

• Will not feed
• Is very hard to wake
• Has trouble breathing
• Looks blue or gray
• Has a seizure
• Is much less active than usual
• Seems very ill

A sick newborn does not need to have a fever to need medical care.

Common Mistakes to Avoid

When parents are worried, it is easy to try to fix the temperature quickly.

These are the mistakes I would avoid.

Waiting for a Higher Number

Do not wait for 101°F, 102°F, or 103°F in a baby under 3 months.

100.4°F or 38°C is the important threshold.

Waiting for Other Symptoms

The baby does not need to have coughing, vomiting, crying, or a rash before you call.

Giving Medicine First

Call your doctor before giving newborn fever medicine.

Trying to Cool the Room

There is no need to chase one exact room temperature.

Keep your baby comfortable and seek medical advice.

Using Cold Water or Alcohol

Do not use these methods.

Assuming It Is Teething

Young newborns are not normally teething.

Do not explain away a true fever as teething.

A Simple Newborn Fever Action Plan

If you remember nothing else from this guide, remember these five points.

1. Use a digital thermometer.
2. A rectal temperature gives the most reliable reading in a young infant.
3. 100.4°F or 38°C or higher is a fever.
4. If the baby is 3 months old or younger, call your pediatrician immediately.
5. Do not give fever medicine before getting medical advice.

How Parents Can Prepare Before a Fever Happens

Preparation makes a stressful night much easier.

Keep these items ready:

• A digital thermometer
• Your pediatrician's phone number
• The after hours clinic number
• Your local emergency number
• A list of your baby's medicines
• Your baby's current weight

Ask your pediatrician during a normal visit what they want you to do if your baby develops a fever at night.

That gives you a plan before you need it.

My Perspective as a Parent and Grandparent

One of the hardest parts of caring for a baby is deciding when a small change is actually important.

A warm forehead may look simple.

But with a very young baby, age changes the answer.

My approach is to prepare before a problem happens.

Keep a thermometer at home.

Know your pediatrician's number.

Know the 100.4°F threshold.

And do not feel that calling the doctor means you have failed to manage something yourself.

Knowing when not to manage something at home is part of good parenting too.

Conclusion

The safest treatment of fever in a newborn begins with recognizing that a young baby's fever needs medical attention, not a collection of home remedies.

If your baby is 3 months old or younger and has a rectal temperature of 100.4°F or 38°C or higher, contact your pediatrician immediately, even if your baby otherwise seems well.

Do not wait for a higher fever. Do not try to cool the fever away. Do not give medicine before getting medical advice.

Your next step: save your pediatrician's number today, keep a digital thermometer ready, and share the 100.4°F rule with everyone who cares for your baby.

References and Medical Sources

This article was reviewed against current public guidance available in August 2026.

1. American Academy of Pediatrics HealthyChildren: Fever and Your Baby
2. American Academy of Pediatrics HealthyChildren: Fever in Newborns and Evaluation of Well Appearing Young Infants
3. American Academy of Pediatrics HealthyChildren: Best Ways to Take a Temperature
4. American Academy of Pediatrics HealthyChildren: Acetaminophen Dosing and Safety
5. NHS: High Temperature and Fever in Children

Frequently Asked Questions

What temperature is a fever in a newborn?

A rectal temperature of 100.4°F or 38°C or higher is considered a fever. If your baby is 3 months old or younger, contact your pediatrician immediately.

Should I take my newborn to the doctor for 100.4°F?

Yes. A baby 3 months old or younger with a rectal temperature of 100.4°F or 38°C or higher needs immediate pediatric medical advice, even if the baby otherwise looks well.

Can I give acetaminophen to my newborn for fever?

Do not give fever medicine to a baby under 3 months before speaking with a healthcare professional. Fever in the first 12 weeks needs medical evaluation.

Can I give ibuprofen to a newborn?

No. Ibuprofen should not be used in babies younger than 6 months unless a doctor specifically directs its use.

Should I cool the room when my newborn has a fever?

You do not need to set the room to one exact temperature. Avoid heavy blankets and too many clothes, but do not try to make your baby cold. A young baby's fever needs medical evaluation.

What is the best way to take a newborn's temperature?

A digital rectal thermometer gives the most reliable and accurate temperature reading for a very young baby. If you are unsure how to use one safely, ask your pediatrician or nurse to show you.

What if my newborn has a fever but seems fine?

Call your pediatrician. A baby 3 months old or younger with a rectal temperature of 100.4°F or 38°C or higher needs prompt medical attention even without other symptoms.

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