We have one piece of bad news and one piece of good news for you. Shall we start with the bad? We're sorry, but it’s very likely that your little adventurer will have a fever at some point during their first year of life (and in many years to come). The good news? Fever in babies—although it understandably worries parents, especially first-time parents—is completely normal and, in most cases, temporary, disappearing almost as quickly as it arrives. In this article, we explain, among other things, what fever is, how to check your baby’s temperature, how to cope with it, and when to consult your doctor.

What is it and when is it considered a fever in babies

As the Spanish Association of Pediatrics (AEP) explains, “fever is a defense mechanism against infections.” In other words, fever is not a disease, but a symptom that shows the immune system is fighting an infection or inflammation to prevent it from spreading—or at least to contain it and slow its progression as much as possible. Therefore, we can define fever as a warning sign, not an alarm , indicating that, in most cases, your baby is coming down with an illness that usually passes without major consequences. However, it is important to remember that viral infections are not the only trigger for fever; for example, some vaccines can cause this reaction in your little adventurer.

But when can you talk about fever in babies? Since normal body temperature varies from person to person and throughout the day (it’s higher in the afternoon), and because body temperature is higher in children between 0 and 3 years old, doctors agree that a baby’s normal body temperature ranges from 36º to 37º (up to 37.5º if the temperature is taken rectally). From there, between 38º and 39º is considered a moderate fever, between 39º and 40º a high fever, and above 40º a very high fever. Below these figures, between 37º and 38º, according to the AEP, it would not be considered a fever, but rather febrile.

How to take the temperature?

It is advisable to measure your baby’s temperature when you feel their body is especially warm. Also, according to the Spanish Association of Pediatrics, you should check it when—whether or not it’s accompanied by a sensation of fever—other signs appear, such as flushed cheeks, shiny eyes, a sensation of cold and chills, tachycardia, increased respiratory rate, irritability, unusual inactivity, and, in the case of boys, an exaggerated retraction of the testes within the scrotum.

To take your baby’s temperature, pediatricians recommend using an electronic thermometer in the armpit for children over two years old. For younger children, an electronic thermometer can also be used rectally, which provides a more accurate result. In any case, forehead strip measurements and ear (otic) thermometers are not recommended due to their low effectiveness.

If you choose the rectal method, it is recommended to wash your hands thoroughly beforehand, clean the thermometer with soap and water, and rinse it. When inserting it, the recommendation is to place it 2 to 2.5 centimeters into the anus, covering the tip of the thermometer with a little Vaseline if necessary to make insertion easier. It is very important to wash the device after taking the measurement. Also, distract your little adventurer with a story or a song so they stay relaxed and the process is easier.

How to act in case of fever in babies

As we’ve said, fever is a completely normal sign in babies, so the most important thing is not to worry more than necessary. From there, the advice is quite straightforward. The main recommendation is to keep your little adventurer hydrated, so make sure your child drinks enough water or, if they are under six months old, that they breastfeed or take formula frequently. It’s true that when they have a fever, little ones often have less appetite, but the trick is to offer smaller amounts more often. In other words: light meals and small portions.

In addition to hydration, the Spanish Association of Pediatrics recommends not overdressing or undressing your baby too much, avoiding alcohol rubs or placing cold water cloths on the forehead, and watching for possible signs of clinical deterioration.

If the temperature exceeds 38º and your little adventurer shows general discomfort, antipyretics can be given every 6/8 hours, according to the dosage recommended on the medication leaflet.

Fever in babies: when to worry and see the pediatrician

Parents, especially first-timers, tend to make an appointment with the pediatrician at the first symptom that catches their attention. And how could it be any different when it comes to a baby’s fever? In any case, it’s not the wrong decision. In fact, pediatricians recommend doing exactly this when babies are under three months old, since before that age it is always advisable for your little one to be evaluated by a medical professional.

After that age, the recommendation is to visit the pediatrician if the fever lasts more than 48 - 72 hours or if, in addition to the fever, your little one is very irritable and drowsy or shows difficulty breathing. Regarding temperature, it is recommended to schedule an appointment with the doctor if it is higher than 39º in babies aged 3 to 6 months, or if it exceeds 40º from six months of age.

Other concerns that require an urgent visit to the pediatrician include the appearance of dark red or purple skin spots that do not disappear when stretching the surrounding skin, neck stiffness, seizures, loss of consciousness or excessive drowsiness, persistent vomiting and/or diarrhea, symptoms of dehydration (dry tongue, absence of saliva, sunken eyes, etc.), or if the child does not urinate or urinates very little.

Before going to the pediatrician, keep in mind that in many cases babies feel very warm, and that doesn’t necessarily mean they have a fever. In fact, one of the most common situations is that a baby is overbundled and, since they do not regulate their temperature very well during the first few weeks of life, their temperature rises and a parent assumes they have a fever. Therefore, it is best to remove some clothing and recheck the temperature after 10 - 15 minutes. If the temperature remains the same (fever), then you should go to the pediatrician or give antipyretics as the situation requires, as mentioned earlier.

Three-day fever

Many children develop what is known as three-day fever as babies or young children, usually between 6 months and 3 years old. It is an acute and contagious viral disease, but mostly harmless, and it is caused by herpesvirus 6. It is characterized by a sudden spike in fever that can reach up to 40 degrees Celsius and lasts for three days, although it can also last four days. After the fever subsides, a rash appears on the body, mainly on the trunk and limbs. This rash can last up to 48 hours.

There is no specific treatment for three-day fever, but it is important to see a pediatrician if the fever is very high to help prevent febrile seizures.

We hope you find this article helpful. And remember: fever in babies is completely natural and, as a general rule, harmless, so this episode that currently has you on edge will soon be just a distant memory. 😉