Call your doctor if your baby is under three months old and has a rectal temperature of 100.4°F (38°C) or higher—this age group needs evaluation for any fever. For babies three months to three years old, call during business hours if the fever reaches 102°F (39°C) or lasts more than a day, or immediately if your baby seems unusually drowsy, has difficulty breathing, won't drink, or shows signs of serious illness like an unusual rash or extreme fussiness.
A fever is your baby's immune system fighting infection, and it is usually a sign the body is working as intended, not a medical emergency. But babies cannot tell you what hurts, and their ability to fight infection improves as they grow, which is why age matters enormously in deciding whether to call. This article walks through what fevers mean, which ones need immediate attention, and how to decide whether to wait or reach out to your pediatrician.
Table of Contents
- How to Take Your Baby's Temperature Accurately
- Fever in Newborns (Birth to Three Months)—Always Call
- Fever in Babies Three Months to Three Years
- Red Flags That Need Immediate Attention
- Understanding Febrile Seizures
- What to Do While Waiting to Call or See the Doctor
- Fever Medication: When and How
- Common Causes of Fever in Babies
- Deciding Between Urgent Care, ER, and a Doctor's Office Visit
- Follow-Up After a Doctor Visit or Call
- Frequently Asked Questions
How to Take Your Baby's Temperature Accurately
A rectal temperature is the most reliable way to know your baby's true temperature, and it is the standard pediatricians use to decide next steps. Insert a lubricated digital thermometer gently about half an inch into the rectum and hold it steady for about one minute, or until the thermometer signals it is done.
Do not force it, and never use a mercury thermometer around a baby. Armpit temperatures run about a degree lower than rectal temperatures and are less reliable, but they work in a pinch if your baby is fussy and you cannot take a rectal reading. Forehead strips and ear thermometers are convenient but notoriously inaccurate in babies, especially when a fever is mild, so skip them if you need to know your baby's true temperature for a doctor call.
Temperature can vary throughout the day—lower in the morning, higher in the evening—so take it when your baby is calm, not right after vigorous play or a warm bath. Write down the temperature and the time you took it, and note whether your baby seems sick or is acting normally.
A baby who is playful, smiling, and interested in feeding may have a fever but could be fighting a minor virus. A baby who is unusually drowsy, does not want to eat, cries differently than usual, or is not making normal sounds needs attention that day, fever or not.
Fever in Newborns (Birth to Three Months)—Always Call
Babies under three months old do not have fully developed immune systems and cannot mount an effective response to certain serious infections. Because the stakes are high and the risks are impossible to assess by appearance alone, pediatricians have a simple rule: any rectal temperature of 100.4°F (38°C) or higher in a baby under three months old warrants evaluation, usually starting with bloodwork.
This does not mean your baby definitely has a serious infection—most fevers at this age are viral and resolve on their own. But the only way to know is a proper workup, which typically includes a blood culture, urinalysis, and possibly a spinal tap (lumbar puncture) to rule out meningitis. These tests sound alarming but are standard safety checks; most come back normal, and the testing itself helps your pediatrician decide on treatment.
Do not wait to see if the fever goes away on its own, and do not give fever-reducing medication hoping it will buy you time. Call your pediatrician or go to the emergency room immediately, especially if your baby was born prematurely or had any complications at birth. Night and weekends do not change this rule—a newborn with a fever is a medical emergency.
A baby who feels warm but you cannot get an accurate temperature reading should still be evaluated. Trust your parental instinct if your baby looks or acts very ill, even if you do not have a confirmed fever. Severe illness in newborns can progress quickly, so erring on the side of caution is always right.
Fever in Babies Three Months to Three Years
Once your baby reaches three months, their immune system is more mature, and mild fevers are often just their body fighting off a common cold or viral infection. A fever of 101°F (38.3°C) in a three-to-six-month-old baby, or 102°F (39°C) in a baby over six months, can usually wait until your pediatrician's office is open the next business day if your baby is acting relatively well and drinking fluids.
The height of the fever matters less than how your baby is behaving and how sick they look and act. A baby with a 103°F (39.4°C) fever who is playing, smiling, and interested in milk is much less concerning than a baby with a 101°F (38.3°C) fever who is unusually quiet, does not respond to your voice, or seems listless.
Older babies and toddlers can also sometimes have very high fevers (104°F or higher) during common viral illnesses like roseola (a viral rash illness) and still recover without complications. Call your pediatrician during business hours if the fever is 102°F (39°C) or higher, or if it lasts more than one day (24 hours at the same height) without any improvement.
If your baby has a fever for more than three days, call even if the temperature is lower. Persistent fevers suggest either a prolonged viral infection or possibly a bacterial infection needing antibiotics. Do not wait if your baby has a fever and also has any warning signs: unusual drowsiness or difficulty waking, difficulty breathing or fast breathing at rest, not drinking anything for six hours or more, a rash that does not blanch (turn white) when you press it, stiffness in the neck, severe ear pain, or crying that sounds strange or abnormal. These warrant an immediate call to your pediatrician or a trip to the ER, not a wait-and-see approach.
Red Flags That Need Immediate Attention
Some symptoms alongside a fever mean your baby needs urgent evaluation, same day, regardless of the fever's height. Difficulty breathing—rapid breathing at rest, grunting, flaring of the nostrils, or retracting (the skin pulling in around the ribs)—suggests a respiratory infection like pneumonia and needs immediate assessment. Severe lethargy, where your baby is difficult to wake or does not respond to your voice, is a warning sign.
A rash that does not fade when you press a glass against it is especially concerning for meningitis or another serious bloodstream infection. Press the glass firmly for several seconds, then release; if the red or purple spots remain visible, that is different from typical diaper rash or heat rash and warrants emergency evaluation. Call 911 or go to the ER if you see this rash combined with a fever.
Difficulty feeding or drinking anything for more than six hours, or visible dehydration (no wet diapers in eight hours, dry mouth, sunken fontanelle or soft spot on the head), means your baby is losing fluids and needs care. Severe pain or crying that sounds abnormal or distressed, especially pain in one ear or the belly, also warrants a call to your pediatrician or ER evaluation.
Fevers that spike above 104°F (40°C) are uncomfortable but not inherently dangerous in children over three months—a high fever alone does not cause brain damage or other permanent harm. But a very high fever combined with any of the above signs needs urgent evaluation. Trust your instinct: if your baby looks or acts critically ill, seek care immediately.
Understanding Febrile Seizures
Some babies between six months and five years old have seizures triggered by a sudden spike in fever, called febrile seizures. The seizure typically lasts under five minutes, involves jerking movements and loss of consciousness, and is frightening to witness but does not cause permanent brain damage or increase the risk of epilepsy later. If your baby has a febrile seizure, stay calm, do not try to restrain the movements, and do not put anything in the mouth.
Lay your baby on their side to keep the airway clear, note how long the seizure lasts, and call your pediatrician or emergency services immediately after it stops. After any febrile seizure, your baby needs evaluation to find the fever's cause and rule out other conditions. If seizures run in your family, mention this to your pediatrician when discussing fever management.
Most babies who have one febrile seizure never have another, and not all babies with fevers have seizures. The risk is about three to four percent of babies with fever—the vast majority do not experience one. Knowing what a febrile seizure looks like and how to respond calmly is more useful than trying to prevent it.
What to Do While Waiting to Call or See the Doctor
Keep your baby comfortable and monitor the fever while you decide whether to call. Dress your baby in lightweight clothing and keep the room at a comfortable temperature—do not overwrap or undress a feverish baby in an attempt to break the fever. A lukewarm bath (not cold) can make your baby feel less uncomfortable, though it will not lower the underlying fever.
Offer fluids frequently: breastfed babies may want to nurse more often, bottle-fed babies may take smaller amounts more frequently, and babies eating solids can have water or broth. Dehydration is the real risk with fever, so getting fluids in matters more than trying to "cool" the fever. A baby who is urinating normally, has moist lips, and is not crying harder than usual is likely hydrated enough.
Keep a written log of your baby's temperature, what time you took it, any symptoms you notice, and how your baby is acting. This information helps your pediatrician assess severity and decide on next steps. Note any vomiting, diarrhea, rash, cough, congestion, or ear pulling. Even if these symptoms seem minor, they guide the diagnosis.
Fever Medication: When and How
Acetaminophen (Tylenol) and ibuprofen (Advil, Motrin) can make a feverish baby more comfortable by lowering the temperature, but they do not speed recovery or prevent complications. They are optional tools, not required, and the decision to use them depends on your baby's comfort, not the fever's height. Many pediatricians suggest giving medication only if your baby seems uncomfortable or is having trouble sleeping.
Do not give ibuprofen to babies under six months old; acetaminophen is the only fever-reducing option for younger infants. For babies six months and older, either medication can be used, but never combine them or alternate between them looking for a better effect. Give only the dose your pediatrician recommends based on your baby's weight, measure carefully with the provided syringe or measuring spoon, and do not repeat more often than directed.
Medication masks the fever—your baby's temperature will drop, but the underlying infection or virus continues. You might feel pressure to medicate so the fever "looks better" during a doctor visit, but your pediatrician wants to know the true fever to help guide treatment. Always tell your doctor what medications you have given and when, and what your baby's temperature was before medication.
Common Causes of Fever in Babies
Viral infections cause the vast majority of fevers in babies and resolve on their own: colds, stomach bugs, roseola (which causes a rash after the fever), hand-foot-and-mouth disease, and respiratory syncytial virus (RSV) all start with fever. Bacterial infections like ear infections, strep throat, or urinary tract infections need antibiotics to resolve and are why your pediatrician may order tests.
Never assume you know the cause—that is your doctor's job. Teething does not cause fever above 101°F (38.3°C); if your teething baby has a higher fever, something else is going on and needs evaluation. Vaccines can cause a low fever within hours or days of administration, but this is mild and brief. Overheating from overdressing or a warm environment can raise temperature, so check your baby's body temperature properly rather than relying on how warm they feel.
Some babies run higher baseline temperatures than others, and some have slightly elevated temperatures with minor viral illnesses. What matters is the overall picture: your baby's behavior, the presence of other symptoms, and whether the fever is isolated or part of a larger illness pattern. Your pediatrician knows your baby's baseline and can put one fever into context.
Deciding Between Urgent Care, ER, and a Doctor's Office Visit
If your pediatrician's office is closed and your baby has a fever with warning signs, go to the emergency room rather than waiting for urgent care. Signs that warrant the ER include difficulty breathing, severe lethargy, a non-blanching rash, suspected meningitis (stiff neck, severe headache in an older baby), or any sign of shock (extreme paleness, weakness, or unresponsiveness).
Urgent care is appropriate for fevers with moderate concerns: a fever of 103°F (39.4°C) in a baby over three months who seems somewhat sick but is drinking and alert, or a fever lasting two to three days that needs evaluation but is not an emergency. Urgent care can do rapid tests, give antibiotics if needed, and refer you to your pediatrician for follow-up.
Call ahead if possible so they know to expect a baby. Your pediatrician's office during business hours is the right first stop for most fevers in babies over three months: fevers of 102°F (39°C) or higher, fevers lasting more than one day, or any fever with bothersome symptoms. Your pediatrician has your baby's full medical history, can examine them properly, and will order tests only if needed.
They also know your insurance and can advise on cost. After-hours nurse lines (through your pediatrician's office or insurance) can help you decide whether to wait or seek care. These nurses ask detailed questions about your baby's symptoms and behavior to help you make the right choice. Do not hesitate to call—that is what they are there for, and they hear these questions constantly.
Follow-Up After a Doctor Visit or Call
If your baby was evaluated and sent home, follow any instructions about fever medication, keeping hydrated, or returning if symptoms worsen. Write down any diagnosis, recommended treatment, and the plan for follow-up—some conditions need repeat visits or lab work a few days later. Ask your pediatrician what symptoms would warrant a second visit or emergency care.
If antibiotics were prescribed, give the full course even after your baby feels better. Stopping early can allow the infection to return and can contribute to antibiotic resistance. If your baby has a reaction to the medication—vomiting, diarrhea, or rash—call your pediatrician to discuss, but do not stop the medication without guidance. Monitor your baby over the next few days.
A fever that was improving and then spikes again, or new symptoms that develop, warrant another call. Many viral illnesses cause fevers that come and go for several days—this is frustrating but normal and does not mean your baby is getting worse. Document what you learn about your baby's pattern: some babies run high fevers easily, others rarely spike a fever.
Knowing this about your own child helps you stay calm in the future and talk more clearly with your pediatrician about what is normal for your baby. Over time, you will build confidence in recognizing when something needs attention and when you can observe at home safely.
Frequently Asked Questions
Is 99°F a fever in a baby?
No. Normal rectal temperature in babies is up to 100.4°F (38°C). A reading of 99°F is normal variation, not a fever, and does not require any action unless your baby also shows signs of illness like poor feeding or unusual fussiness.
Can I give my baby fever medicine to prevent febrile seizures?
No. Fever-reducing medicine does not prevent febrile seizures. If your baby has a family history of febrile seizures, tell your pediatrician, but treating fever with medication is only for comfort, not prevention.
How long can a baby safely have a fever?
Viral fevers typically last three to five days, though some last longer. Fevers lasting more than three days warrant a call to your pediatrician to check for a bacterial infection or other treatable cause.
Should I wake my baby to give fever medicine?
No. Fever medicine is optional and only for comfort. If your baby is sleeping peacefully, let them sleep—rest is more important for fighting infection than bringing the fever down.
What should I do if my baby's fever comes back after medicine wears off?
This is normal. The medicine wears off in four to six hours (depending on which one you use), and the temperature rises again. You can redose if your pediatrician approves the schedule, or simply watch your baby without medication between doses.
Can a high fever cause brain damage?
No. Fevers from illness do not cause brain damage, even very high fevers (104°F or higher). Only extreme hyperthermia from heat exposure—temperatures above 108°F—risks damage. Febrile seizures also do not cause lasting brain harm.
