How to Monitor Your Temperature for Flu, COVID-19, and Other Illnesses

Fever is often the body’s natural response to infection. But when does it become a cause for concern? And how do you monitor it accurately at home?

Whether you’ve caught the flu, tested positive for COVID-19, or are dealing with another viral infection, keeping track of your temperature helps you understand your symptoms and decide when it’s time to rest, isolate, or seek medical advice.

Why Monitoring Your Temperature Matters

Fever is one of the most common early signs that your immune system is fighting something off. For illnesses like COVID-19 and influenza, it’s often one of the first noticeable symptoms. A rising temperature can signal that your body is reacting to a virus, while a falling temperature could be a sign of recovery—or, in some cases, another underlying issue.

Monitoring your temperature regularly during an illness can help you:

·         Recognise if your symptoms are worsening.

·         Determine whether over-the-counter medication is working.

·         Know when to seek medical support.

·         Track how long you’ve had a fever (helpful for isolation or return-to-work decisions).

If you’re a parent, carer, or managing an underlying health condition, regular temperature checks can be even more important.

What’s a Normal Temperature?

Normal body temperature can vary slightly from person to person, but it’s generally between 36.1°C and 37.2°C. Your temperature may also fluctuate throughout the day—usually lower in the morning and higher in the evening.

Here’s a general breakdown of temperature levels:

·         Normal: 36.1°C – 37.2°C

·         Low-grade fever: 37.3°C – 38.0°C

·         Moderate fever: 38.1°C – 39.0°C

·         High fever: 39.1°C – 40.0°C

·         Very high: 40.1°C and above – seek urgent medical advice

It’s not just the number that matters—it’s how long your temperature stays high and whether other symptoms are present.

Choosing the Right Thermometer

There are several types of thermometers available, but for most homes, a digital thermometer is the best option. These devices are accurate, quick, and easy to use. You can find versions that are suitable for oral, armpit (axillary), or rectal readings.

You may also come across:

·         Infrared (no-touch) thermometers: Useful for quick checks, especially with children.

·         Ear thermometers: Provide fast readings but can be affected by earwax or incorrect positioning.

·         Forehead strips: Not as reliable for clinical readings.

For long-term tracking, especially if you need to log highs and lows over several days, a max min digital thermometer is helpful. It records the highest and lowest temperatures since the last reset, giving you a snapshot of how your body temperature has fluctuated throughout the day or night.

In clinical or care settings, data loggers can also be used to record ambient room or storage temperatures to ensure patients or medicines are kept in safe conditions. Some advanced models even monitor patient temperatures directly, syncing data to cloud platforms for review by healthcare professionals.

How to Take a Temperature

To get an accurate reading, it’s important to use your thermometer correctly and follow the instructions specific to your thermometer model. Take your temperature at the same times daily, such as morning and evening.

·         Choose the same method each time (oral, axillary, etc.) to keep readings consistent.

·         Wait 15–30 minutes after eating, drinking, or exercising before taking your temperature.

·         Clean your thermometer after each use with rubbing alcohol or soapy water.

Interpreting Your Results

A mild fever (around 38°C) can be managed at home with rest, fluids, and paracetamol if needed. If your fever goes above 39°C, or lasts more than 3 days, it’s time to call your GP or NHS 111.

If you have a persistent high fever alongside symptoms like chest pain, shortness of breath, or confusion, seek immediate medical attention.

If you’re recovering from COVID-19 or flu, a consistent drop in temperature toward the normal range is generally a good sign. If your fever disappears but other symptoms worsen, further advice may be needed.

Keeping a Temperature Log

Keeping a simple log can help you and your healthcare provider make sense of your illness. This includes the time and date of each reading, the temperature itself, any symptoms (e.g. chills, fatigue, headache) and medications taken.

Some digital thermometers come with built-in memory, or you can use an app to track readings. In more advanced setups—such as care homes or clinical environments—data loggers can be used to continuously monitor and record temperature data for patients or storage environments.

Logging helps spot patterns and provides valuable information during consultations, especially if you need to speak to a doctor remotely.

When to Seek Medical Advice

Call NHS 111 or your GP if:

·         Your fever lasts more than 3 days

·         You’re experiencing persistent fatigue, dehydration, or dizziness

·         You’re at higher risk due to age, pregnancy, or chronic illness

·         You’re taking medications that affect the immune system

Seek urgent medical attention if:

·         Your temperature goes above 39°C

·         You’re having trouble breathing or chest pain

·         You feel disoriented, confused, or are struggling to stay awake

·         A child under 3 months has a temperature above 38°C

Final Thoughts

Monitoring your temperature is a simple but valuable way to stay informed about your health. Using reliable tools like a digital thermometer ensures accuracy, while more advanced solutions such as data loggers can support ongoing tracking when needed. Staying consistent and paying attention to your readings can help you make better decisions about rest, treatment, or when to seek medical advice.