What is considered a fever under the armpit?

September 28, 2025 •

4 min read

According to reputable sources like the Cleveland Clinic and Seattle Children's, an axillary (underarm) temperature of 99°F (37.2°C) or higher is generally considered a fever. Understanding what is considered a fever under the armpit is important, but this measurement method is less accurate than others and should be viewed with caution.

Quick Summary

An armpit temperature reading of 99°F (37.2°C) or more is the widely accepted threshold for a fever, though accuracy is lower than oral or rectal methods. This article details the specific temperature guidelines for different age groups, how to correctly measure armpit temperature, and when to seek medical advice.

Key Points

Fever Threshold: For adults and children, an armpit temperature of 99°F (37.2°C) or higher is generally considered a fever, though accuracy is lower than other methods.
Infant Exception: For very young infants (under 2-3 months), even a slightly elevated temperature is a concern, and confirming with a rectal reading is recommended.
Less Accurate: Axillary readings are lower than oral and rectal measurements because they measure surface skin temperature, not core body temperature.
Add a Degree: Some pediatricians recommend adding 0.5°F to 1°F to an armpit reading to estimate a more accurate core temperature, but always inform your doctor if you do this.
Proper Technique: A dry armpit, snug placement, and waiting for the thermometer's beep are crucial for minimizing inaccuracies.
When to See a Doctor: Contact a doctor for a persistent fever, a very high fever (e.g., over 103°F in adults), or if other concerning symptoms like a stiff neck or confusion are present.

Understanding the Basics of Axillary Temperature

An axillary temperature, or underarm reading, is a common and non-invasive method for screening a person's body temperature, especially in children and infants. However, it's crucial to understand that an armpit reading is a surface skin temperature, not a core body temperature, which makes it less accurate than oral, rectal, or temporal methods. Due to this difference, the fever threshold is typically lower for an armpit reading compared to an oral one.

What is a normal axillary temperature range?

Normal body temperature can vary from person to person and fluctuate throughout the day, often being higher in the evening. For adults, a typical armpit temperature range is 95°F to 98.5°F (35°C to 36.9°C), with an average around 96.7°F (36°C). For infants, the normal range is often slightly higher, around 97.7°F to 99.5°F (36.5°C to 37.5°C). Knowing an individual's normal baseline temperature is important for interpreting any elevated reading.

Specific Guidelines for an Armpit Fever

Because it is a less precise method, there can be slight variations in the fever threshold reported by different health organizations. However, a common and conservative guideline is widely accepted.

Axillary fever guidelines for adults

For adults, an underarm temperature of 99°F (37.2°C) is often used as the benchmark for a fever. While this is a general guideline, it is not a definitive diagnosis and should be interpreted in the context of other symptoms. If you are able, taking an oral temperature is recommended for a more accurate reading to confirm the fever.

Axillary fever guidelines for children and infants

Taking an armpit temperature is a safe and common method for screening fever in younger children. However, the threshold for concern can be different depending on the child's age.

For children over 2 months: An underarm temperature of 99°F (37.2°C) or higher is considered a fever by some sources.
For infants under 2 months: Due to their delicate nature, even a slight fever is cause for serious concern. St. Jude's hospital, for example, defines a fever for a newborn under two months as an underarm temperature of 99.4°F (37.4°C) or higher. If an armpit temperature is elevated in a very young infant, it is highly recommended to confirm with a more accurate rectal reading and contact a doctor immediately.

How to take an armpit temperature correctly

To minimize inaccuracies, proper technique is essential when taking an axillary temperature with a digital thermometer. Follow these steps for the most reliable screening:

Ensure the armpit is dry: Pat the area completely dry with a towel, as moisture can affect the reading.
Turn on the thermometer: Make sure the digital thermometer is ready to use.
Position the tip: Place the tip of the thermometer high in the center of the armpit, ensuring it touches only skin and not clothing.
Hold arm snugly: Bring the person's arm down and hold it firmly against their body to keep the thermometer in place.
Wait for the beep: Hold the thermometer in position until it beeps, signaling that the reading is complete.
Read and record: Note the temperature displayed on the screen.

Comparing Armpit Temperature to Other Methods

Different methods of taking a temperature produce different readings. It's important to know the typical variation to interpret the results correctly.


Measurement Method	Typical Reading Compared to Oral	Notes on Accuracy
Oral (by mouth)	Baseline	Highly accurate when done correctly
Axillary (armpit)	0.5°F to 1°F (0.3°C to 0.6°C) lower	Less accurate; useful for screening
Rectal (in the rectum)	0.5°F to 1°F (0.3°C to 0.6°C) higher	Most accurate, especially for infants
Ear (tympanic)	0.5°F to 1°F (0.3°C to 0.6°C) higher	Can be less accurate before 6 months of age
Forehead (temporal)	Similar to axillary, but with variations	Can be affected by sweat or technique

Factors that can influence an underarm reading

Several factors can cause an armpit temperature reading to be less than accurate or misleading:

Inadequate skin-to-thermometer contact: The thermometer must be held firmly against the skin for the entire duration.
External temperature: A cold room or recent activity can impact the surface temperature of the skin.
Moisture or sweat: Wet skin can produce an inaccurate, often lower, reading.
Recent physical activity: Exertion can cause a temporary rise in body temperature.
Over-the-counter medication: Taking fever-reducing medication before the measurement can mask a true fever.
Wearing heavy clothing: This can increase skin temperature and provide a false reading.

When to contact a healthcare provider

While a mild fever can often be managed at home, it is essential to know when to seek medical advice.

Infants under 3 months: Call your child's provider immediately for any temperature of 100.4°F (38°C) or higher (rectal), and especially if an armpit reading is elevated, as armpit readings can underestimate the true core temperature.
All ages: Seek immediate medical attention if a fever is accompanied by worrying symptoms such as severe headache, rash, mental confusion, a stiff neck, difficulty breathing, or seizures.
Persistent fever: Contact a doctor if a fever lasts for more than three days (children) or five days (adults).

For more detailed guidance on fever management and concerning symptoms, consult a resource like the Mayo Clinic's guide on fevers.

Conclusion: Context is key

In conclusion, while 99°F (37.2°C) is a standard threshold for an axillary fever, this measurement is best used as a screening tool rather than a definitive diagnosis. It is important to use the correct technique, be aware of factors that can influence the reading, and consider confirming with a more accurate method if a fever is suspected, especially for young children. Always consider the person's overall behavior and other symptoms, and know when to seek professional medical advice.

Frequently Asked Questions

No, an armpit (axillary) temperature is less accurate than oral or rectal measurements because it reflects surface skin temperature rather than the internal core temperature. Rectal temperature is considered the most accurate, especially for infants.

A normal armpit temperature range for a baby is generally around 97.7°F to 99.5°F (36.5°C to 37.5°C). However, any elevated temperature in an infant, especially under three months, should be discussed with a doctor.

While some guidance suggests adding 0.5°F to 1°F to an armpit temperature to estimate a more accurate core temperature, it is best to rely on a more accurate method, like an oral or rectal reading, for confirmation. If you do adjust the reading, be sure to inform your healthcare provider.

Inaccurate readings can be caused by a wet armpit, recent physical activity, cold external temperatures, or a poor seal of the thermometer against the skin. Wearing heavy clothing can also cause a falsely high reading.

The armpit method is best used for general screening, especially for children and infants where a less invasive method is preferred. If you suspect a fever based on an axillary reading, or if other symptoms are present, it's wise to confirm with a more accurate method if possible.

You should follow the manufacturer's instructions for your specific digital thermometer. Generally, you will keep it in place until the thermometer beeps, which signals that the reading is complete. This is often between 10 seconds and a minute.

A reading of 98.6°F (37°C) in the armpit is higher than the average axillary temperature. Since armpit readings are typically lower than the standard oral 98.6°F, this reading could be considered a low-grade fever and may warrant further monitoring.