Fever 101: What Parents Should Know

| Patient EducationPediatric Care

What Is a Fever?

A fever occurs when the body's temperature goes above average, usually around 99 °F (37.2°C) for underarm readings and 100.4 °F (38°C) for rectal, forehead or ear readings. This elevation in temperature is a reaction to infections or illnesses, triggering the immune system to fight them off. In most cases, fevers do not cause significant concern and usually diminish as the underlying condition resolves.

man on phone holding thermometer next to kid

What Is the Correct Thermometer to Use?

The most precise way to measure body temperature is with a digital thermometer, suitable for oral, rectal or armpit use. We recommend digital thermometers instead of mercury glass ones, as the latter pose a hazard of mercury poisoning when broken. Alternatives like tympanic (ear) and temporal artery thermometers are available, but their accuracy can vary depending on age and proper use.

Here is a quick guide on where to take the temperature and the most accurate methods:

  • Rectal: Most accurate for all ages, especially infants under three months.
  • Forehead: Next most accurate, especially for infants under three months.
  • Ear: Accurate if done properly, but only recommended after six months of age due to inaccuracy.
  • Armpit: Least accurate, but useful for screening at any age. Recheck with a more precise method if an armpit temperature shows a fever.

How to Take a Temperature

For precise body temperature measurement, get a clean and functional thermometer. Wash hands before use and place the thermometer where the directions describe. To ensure accuracy, one should refrain from eating or drinking for at least 5 minutes before measurement. Rapid temperature progression could mean you need medical support. Contact a pediatrician or primary care provider if the fever worsens.

When checking rectal temperature in infants up to one year old, position their stomach on your lap or their back with legs pulled up. Apply petroleum jelly on the thermometer and anus, gently inserting it no more than 1 inch (1/2 inch for under six months). Hold the child still until the thermometer beeps after about 10 seconds. A reading over 100.4 °F (38°C) indicates a fever, but avoid this method in children with certain health conditions like cancer or weakened immunity.

For an armpit temperature screening, place the thermometer tip in a dry armpit, closing it by holding the elbow against the chest for about 10 seconds. Ensure the thermometer tip stays covered by skin. A temperature above 99.0°F (37.2°C) suggests a fever, and if uncertain, use rectal or forehead temperature methods.

For children aged six months and older, pull the ear backward and aim the ear probe between the opposite eye and ear. This quick and comfortable method takes less than 2 seconds but ensure the temperature is taken indoors after 15 minutes to avoid inaccuracies. Earwax, infections, and ear tubes do not affect the accuracy of the reading.

When measuring forehead touch temperature, place the thermometer sensor head at the center of the forehead, sliding it toward the top of the ear while keeping contact with the skin. Read the temperature on the display screen. This method is quick, doesn't require cooperation and is discomfort-free. Ensure the thermometer is digital, as forehead strips are not accurate.

Aim the thermometer at the center of the forehead for a no-touch forehead temperature, staying less than 1 inch away without touching the forehead. Kepp the thermometer still, then press the measurement button. This contact-free method is suitable for all ages and provides a convenient and quick temperature reading.

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When a Fever Is a Cause for Concern

Fevers below 103 °F (39.4°C) are not usually a cause for concern. Home remedies like over-the-counter medicine are adequate in most instances. Yet, if the fever surpasses 102 °F (38.9°C) and persists despite home treatment, consult your provider. Seek professional care if the fever exceeds five days, rises above 104 °F (40°C), or symptoms like discoloration or diarrhea emerge.

Practical Tips for Managing a Fever

To address mild fevers below 101 °F (38.3°C), it is essential to:

  • Stay well-hydrated: Encourage plenty of fluids to prevent dehydration, especially in infants and young children.
  • Rest: Allow the body to focus on fighting the illness by getting plenty of sleep.
  • Lukewarm bath: Consider a lukewarm bath to help slightly reduce the fever. Avoid using cold baths or sponging, as they can be counterproductive and cause shivering, raising the body temperature.

Over-the-counter medications like ibuprofen can improve comfortability, but always consult a doctor before administering medication to a child.

If the fever persists or occurs with severe symptoms, immediately seek guidance from a healthcare provider.

About the Author

Jenna Ali MD

Dr. Jenna Ali is a pediatrician with Schneck Pediatrics in Seymour, Indiana.