An accurate temperature reading can be the difference between catching an illness early and missing important warning signs. Yet many people unknowingly make common mistakes that lead to inaccurate measurements. Whether you're caring for a newborn, managing your own health, or looking after elderly family members, mastering proper temperature-taking technique is an essential skill.
This guide walks you through the correct methods for each type of temperature measurement, helping you get reliable readings every time.
Before You Begin: Essential Preparation
Regardless of which measurement method you use, proper preparation sets the foundation for accuracy:
- Wait 30 minutes after eating, drinking, or physical activity
- Ensure the person is calm – crying or agitation can temporarily elevate temperature
- Check your thermometer's battery – low batteries cause unreliable readings
- Clean the thermometer before and after each use
- Read the manufacturer's instructions – different models may have specific requirements
Take multiple readings and record them. If readings vary significantly, wait a few minutes and measure again. Consistent technique yields consistent results.
Forehead (Temporal Artery) Temperature
Non-contact infrared thermometers have become increasingly popular due to their convenience and hygiene benefits. Here's how to use them correctly:
Step-by-Step Instructions
- Ensure the forehead is clean and dry. Wipe away any sweat, makeup, or hair products that could interfere with the reading.
- Remove hats or headbands and wait 10-15 minutes if the person has been outdoors in extreme temperatures.
- Position the thermometer correctly. Most models require placement 3-5 centimetres from the centre of the forehead. Check your specific model's instructions.
- Hold steady and press the measurement button. Keep the thermometer still until the reading is complete (usually 1-3 seconds).
- Read the display and record the temperature.
Common Mistakes to Avoid
- Measuring immediately after coming indoors from cold or hot weather
- Taking readings through hair covering the forehead
- Holding the thermometer too far away or at an angle
- Measuring over the temporal artery (side of forehead near hairline) when the device is designed for centre-forehead measurement
Key Takeaway
Forehead thermometers are excellent for quick screening but may be less accurate than other methods. If a reading seems inconsistent with symptoms, confirm with an ear or oral measurement.
Ear (Tympanic) Temperature
Ear thermometers measure infrared heat from the eardrum, providing readings close to core body temperature. They're fast and generally well-tolerated by children.
Step-by-Step Instructions
- Ensure the ear canal is clear. Excessive earwax can affect readings. Do not use if there's an ear infection or recent ear surgery.
- Use a clean probe cover if your model requires one. Never reuse disposable covers.
- Straighten the ear canal by gently pulling the ear:
- For children under 12 months: Pull the ear straight back
- For children over 12 months and adults: Pull the ear up and back
- Insert the probe gently into the ear canal, creating a seal. Do not force it.
- Press the button and hold steady until the thermometer beeps (usually 1-2 seconds).
- Remove and read the temperature display.
Tips for Accurate Ear Readings
- Use the same ear consistently when tracking temperature over time
- Wait 15 minutes if the person has been lying on that ear
- Avoid measuring directly after swimming or bathing
- Take 2-3 readings and use the highest one
Ear thermometers are not recommended for infants under 6 months. Their ear canals are too small for accurate readings. Use a rectal or forehead thermometer instead.
Oral Temperature
Oral temperature measurement is a traditional and reliable method for older children and adults. Digital thermometers have made this method faster and safer than older mercury models.
Step-by-Step Instructions
- Wait at least 15 minutes after eating, drinking, or smoking.
- Place the thermometer tip under the tongue, toward the back of the mouth in the "heat pocket" on either side.
- Close lips firmly around the thermometer. Breathing through the nose helps maintain accuracy.
- Keep the thermometer in place until it beeps (typically 30-60 seconds for digital models).
- Remove and read the temperature immediately.
Ensuring Accuracy
- The probe must stay in the same position throughout measurement
- Don't talk or bite down on the thermometer
- For children, ensure they can hold the thermometer properly without biting it
- Cold drinks can artificially lower readings for up to 20 minutes
Underarm (Axillary) Temperature
While less accurate than other methods, underarm measurement is non-invasive and suitable for screening purposes. It's often used when other methods aren't practical.
Step-by-Step Instructions
- Ensure the armpit is dry. Pat dry with a towel if necessary.
- Place the thermometer tip in the centre of the armpit.
- Hold the arm firmly against the body throughout the measurement.
- Wait for the full measurement cycle – this method takes longer than others (3-5 minutes for accurate reading).
- Read and record the result.
Underarm temperatures are typically 0.5-1°C lower than core body temperature. To estimate core temperature, add 0.5°C to your underarm reading, though this adjustment varies by individual.
Which Method Should You Use?
The best method depends on age, situation, and available equipment:
- Newborns to 3 months: Rectal (most accurate) or forehead
- Infants 3-12 months: Rectal, forehead, or ear (if over 6 months)
- Toddlers 1-4 years: Ear, forehead, or underarm for screening
- Children 4+ and adults: Oral, ear, or forehead
- Screening multiple people: Non-contact forehead
Recording and Tracking Temperatures
When monitoring an illness, keeping accurate records helps you and healthcare providers track progression:
- Note the time of each measurement
- Record the method used
- Document any medications given and when
- Note other symptoms present
Many modern thermometers include memory functions that store previous readings, making tracking easier. Consider using a dedicated notebook or health tracking app for comprehensive records.
Troubleshooting Inconsistent Readings
If you're getting wildly different readings, consider these factors:
- Operator technique: Review the instructions and ensure consistent positioning
- Environmental factors: Extreme room temperatures can affect some thermometer types
- Battery power: Replace batteries if the low battery indicator appears
- Thermometer accuracy: All thermometers can drift over time; consider testing against a known accurate device
When in doubt, take three readings using the same method and average them, or use the highest reading for fever assessment.