How Do I Know When My Child’s Fever Is Serious?

Author: Isaac Oni B.Pharm

Medical Reviewer: Azuka Chinweokwu Ezeike, MBBS, FWACS, FMCOG, MSc (PH)

Highlights 

• Fever in children is a common concern for parents and one of the most frequent complaints in paediatric emergency department visits.
• Fever is usually a sign that your child’s body is fighting an infection, not a disease on its own.
• The child’s behaviour often matters more than the exact temperature reading.
• Certain warning signs mean a fever may be serious and need urgent medical care.
• Knowing when to act can reduce anxiety and help keep your child safe.

Introduction

Few things make parents anxious faster than discovering their child has a fever. One moment, your child seems fine, and the next, they feel unusually warm when you try to feel their temperature with your hands. It’s natural to worry and wonder if something serious is happening.

A fever is simply a rise in body temperature above normal. It is a body response characterised by an elevation of body temperature above normal daily variation [1]. Research shows that some childhood fevers are caused by mild viral illnesses and resolve without complications; however, fever may also be a sign of a serious disease  [2]. 

While fevers can bring worries, they are usually part of the body’s normal defence system. The real challenge for parents is knowing how to draw the line between a fever that signals danger and when it is harmless.

In this guide, you will understand how to measure your child’s fever correctly, understand its severity, recognise warning signs, manage mild fever at home, and know when to seek medical help.

What Is a Fever?

A fever is generally defined as a body temperature of 38°C (100.4°F) or higher when accurately measured with a thermometer. Fever itself is not an illness but a symptom of an underlying process, usually infection or inflammation.

Research shows that fever alone is a poor indicator of serious illness. Fever should be assessed alongside other things, such as the child’s overall physical appearance, behaviour, and symptoms.

Why Does Fever Occur in Children?

Fever in children could be due to several reasons. Fever in children is most commonly caused by:

• Viral infections (colds, flu)
• Bacterial infections such as pneumonia, sore throat (pharyngitis)
• Parasitic infections like malaria, giardiasis and roundworm

When the body detects an infection, the immune system releases chemicals that raise body temperature. This temperature rise is a body's way of slowing down the growth of bacteria and viruses and improving immune response [3]. Hence, we can say that fever is a beneficial physiological response in children, which happens most of the time they have it.

Other causes of fever in children include:

• Vaccinations
• Overheating, otherwise known as hyperthermia
• Inflammatory conditions such as Multisystem Inflammatory Syndrome in Children (MIS-C)

How to Measure Fever Correctly

Before concluding on the severity of your child's fever, you need to know how to accurately measure the body's temperature of your child.

Below are some of the ways to measure a child's temperature.

• Rectal thermometers:

 Rectal thermometers are digital thermometers used to measure the core body temperature through the anus. It is considered to be the most accurate method of measuring the body’s temperature, especially for infants between 0-3 months old. While this method is considered the gold standard to measure body temperature, you should note the following safety tips:

• Lubricate the tip with petroleum jelly to minimise friction before inserting to the anus
• The depth of insertion should be 1-2cm
• Hold in place until the device beeps
• Do not force past any resistance during insertion
• Avoid if the baby has any form of anorectal malformations as this can cause perforation if the rectum is malformed or absent.

• Oral thermometers: 

These are generally suitable for children ≥5 years old who can cooperate and follow instructions. Oral thermometers are used by placing the tip of the thermometer under the tongue and asking your child to close their lips around it until the device beeps or gives other signals that the temperature is ready to be read.

• Axillary (Armpit) thermometers: 

An axillary thermometer measures body temperature under the armpit. It is a noninvasive, safe, and easy-to-use method commonly for infants and young children. While convenient, it is generally less accurate than rectal or oral methods. 

This is because with an axillary thermometer, only the tip of the thermometer is against your child’s skin and not inside their body. Hence, the reading does not represent the true internal temperature. To account for this, you should add 0.3 to 0.6°C to the axillary thermometer reading.

• Ear (tympanic) thermometers: 

These thermometers make use of an infrared scanner to measure the temperature inside the ear canal. However, the presence of earwax or a small, curved ear canal can affect its accuracy.

• Temporal Artery (Forehead): 

A temporal artery thermometer is similar to tympanic thermometers. It is a non-invasive device that makes use of infrared technology to measure the body’s temperature by scanning the temporal artery on the forehead. It provides rapid and accurate readings in seconds, does not cause any physical discomfort, and is suitable for all ages. 

However, they could be less accurate when used in direct sunlight or extreme cold. The presence of sweat on the forehead could also affect its accuracy.

Mercury thermometers are no longer recommended due to the risk of exposure to mercury if broken. Inaccurate measurement can lead to unnecessary anxiety and inappropriate treatment decisions. Digital thermometer is currently the recommended option.

Standard references for fever definition in children are based on the route used in measuring the temperature:

• Rectal/Oral:  ≥38°C
• Axillary:  ≥37.5°C
• Ear/Tympanic:  ≥38°C

Classification based on Fever Severity

Fever severity is often grouped into levels to help guide care [4].

Low-Grade Fever (37.5 - 38.0°C)

• Common in viral infections• Child often remains active and alert

Moderate Fever (38.1 - 39.0°C)

• May cause discomfort• Usually manageable at home if the child is drinking fluids and responsive

High Fever (39.1 - 41°C)

• Requires closer observation• May need medical advice depending on other observed symptoms

Hyperthermia (>41°C)

• Requires urgent medical attention

Warning Signs of  a Serious Fever in Children

Parents should seek urgent medical care if a fever is accompanied by:

• Fever more than 38°C, especially in children less than 3 months old
• Difficulty or fast breathing patterns
• Extreme sleepiness, confusion, or poor responsiveness
• Persistent vomiting or inability to tolerate fluids
• Signs of dehydration, which are dry mouth, a few wet nappies, and sunken eyes
• Seizures or convulsions
• Stiff neck
• Rash that does not fade when pressed
• Pale, bluish, or mottled skin
• Fever lasting more than 72 hours

Febrile Seizures: What Parents Should Know

Some children may experience seizures (convulsions) triggered by a sharp rise in temperature. Such febrile seizures can be frightening; however, they are generally not associated with long-term brain damage or epilepsy.

A medical assessment is recommended after the first episode to rule out any other serious potential causes [5].

Parental Anxiety and “Fever Phobia”

Many parents fear fever itself, a phenomenon known as fever phobia. Evidence shows that parents often overestimate the dangers of fever, worrying about brain damage or death [6].

Every parent should know this:• Fever alone rarely causes harm, but every fever should be evaluated• Brain damage from fever is extremely rare• The child’s behaviour matters in addition to the temperature

Home Care for Mild Fever

If your child has a mild fever but is alert, drinking fluids, and not in distress, home care is usually safe to administer.

Supportive Care Measures

• Encourage fluids such as water, breast milk, or oral rehydration solution• Dress the child lightly• Keep the room comfortably cool• Allow rest, but do not force sleep

Use of Fever-Reducing Medicines

Paracetamol or ibuprofen may be used to relieve discomfort rather than to “normalise” temperature. Evidence suggests that fever-reducing medicines do not shorten illness duration but can improve comfort [7,8].

Do not give Aspirin to children as it is linked to Reye’s syndrome.

Other things to avoid include:

• Cold baths or ice sponging

• Over-wrapping the child

• Alternating medicines without professional advice

When to Seek Medical Attention

Medical advice should be sought if:• Fever persists beyond 48–72 hours• Fever keeps returning• The child refuses to take fluids or symptoms are worsening• You are worried or feel something is not right

Conclusion

Fever is one of the most common reasons parents seek medical advice for their children. While it can be frightening, some fevers are a normal response to infection and can be safely managed at home.

Understanding how to measure fever correctly, recognising warning signs, and focusing on your child’s overall behaviour, not just the temperature, can help you make informed decisions. However, as a parent, if your instinct suggests seeking medical help, do not hesitate.

References

1. National Collaborating Centre for Women's and Children's Health (UK). Feverish Illness in Children: Assessment and Initial Management in Children Younger Than 5 Years [Internet]. PubMed. London: Royal College of Obstetricians and Gynaecologists (UK); 2013. Available from: https://pubmed.ncbi.nlm.nih.gov/25340238/

2. Holt J, White L, Wheaton GR, Williams H, Jani S, Arnolda G, et al. Management of fever in Australian children: a population-based sample survey. BMC Pediatrics [Internet]. 2020 Jan 13;20. Available . from: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC7812885/

3. Akilzhanova, Ainur, et al. “Fever as an Important Resource for Infectious Diseases Research.” Intractable & Rare Diseases Research [Japan], vol. 5, no. 2, 2016, pp. 97–102. https://doi.org/10.5582/irdr.2016.01009

4. Balli S, Sharan S, Shumway KR. Physiology, fever [Internet]. PubMed. Treasure Island (FL): StatPearls Publishing; 2023. Available from: https://www.ncbi.nlm.nih.gov/books/NBK562334/

5. Febrile Seizures: Clinical Practice Guideline for the Long-term Management of the Child With Simple Febrile Seizures. Pediatrics [Internet]. 2008 Jun 1;121(6):1281–6. Available from: http://pediatrics.aappublications.org/content/121/6/1281

6. Cengiz M, Gündüz BÖ. Maternal attitudes and practices toward childhood fever: insights from a large-scale survey of over 3,000 mothers. BMC Pediatrics [Internet]. 2025 Nov 24;25(1). Available from: https://pmc.ncbi.nlm.nih.gov/articles/PMC12642302/

7. Green C, Krafft H, Guyatt G, Martin D. Symptomatic fever management in children: A systematic review of national and international guidelines. Catalá-López F, editor. PLOS ONE. 2021 Jun 17;16(6):e0245815. Available from: https://journals.plos.org/plosone/article?id=10.1371/journal.pone.0245815

8. Mohanta MP, Khuntdar B, Panda M, Mohanty N. Recent Concepts in Fever Management: Improving Our Clinical Practice. Research and Reviews in Pediatrics. 2025 Jan;26(1):15–8. Available from: https://journals.lww.com/rrp/fulltext/2025/01000/recent_concepts_in_fever_management__improving_our.4.aspx

Disclaimer:
The information provided on this website is for general educational and informational purposes only. It is not intended to replace professional medical advice, diagnosis, or treatment. Always seek the advice of your physician or other qualified health provider with any questions you may have regarding a medical condition.

Published February 20, 2026