What is a CGM? How it works and how to apply one

In the world of health tech, wearable devices have exploded in popularity to help people track steps, heart rate, sleep, and more. Continuous glucose monitors, or CGMs, are a subset of these wearables that help people track their glucose levels. 

While CGMs aren’t new — they’ve been around for well over a decade for those with type 1 and type 2 diabetes — more research is pointing towards the benefits of CGMs for people without diabetes.¹ 

So, what exactly is a CGM and how does it work? 

CGMs use a sensor filament inserted just under the surface of the skin to measure glucose in your interstitial fluid, which is the thin layer of fluid surrounding your cells.

What is a CGM? 

A continuous glucose monitor, or CGM, is a small biowearable device worn on the body that measures your glucose around the clock. Most CGMs connect to a smartphone app so you can see your real-time glucose data right on your phone. 

Unlike traditional blood glucose meters that require a finger prick blood sample, CGM technology uses a tiny sensor to measure glucose in the interstitial fluid (a thin layer of fluid surrounding the cells of the tissue below your skin). The sensor stays on your body with an adhesive and connects to a transmitter, which wirelessly sends data to a dedicated receiver or smartphone app.   

CGM readings from interstitial fluid are converted to approximate blood glucose levels. While they tend to trend similarly, CGM may lag behind actual blood glucose by about 3 to 5 minutes.² A major benefit of CGMs is once you apply the sensor, it provides continuous feedback compared to a finger prick blood test that measures glucose immediately — but only for that moment. 

CGMs, such as Lingo, allow you to continuously track your glucose and view data in real time, which offers valuable insights into your responses to food, exercise, and sleep. This helps you make informed decisions and find what works for your body 

Why use a CGM if you don’t have diabetes? Research suggests less glucose exposure is associated with greater metabolic health.¹ And using a CGM and limiting glucose spikes can lead to several health benefits both in the short term and over time.¹ 

CGMs allow you to continuously track your glucose in real time, offering valuable insights into your responses to lifestyle factors like food, exercise, and sleep. Compared to a finger prick blood test that measures glucose immediately — but only for that moment. 

How you apply a CGM 

Applying a CGM is a straightforward process that you can do at home. It’s best to apply on clean and dry skin, and prepare the site (usually on the back of the arm) with an alcohol wipe to help prevent any irritations or infections. 

Most CGMs come with an easy-to-use applicator you push down on the site until the biosensor attaches in place. This process inserts a sensor filament less than 0.4 millimeters (mm) in diameter, 5 mm under the surface of the skin to measure glucose in your interstitial fluid. The CGM stays on the skin with an adhesive and connects to your phone or receiver wirelessly, allowing it to be used with no charge. 

After the CGM is in place, many devices require activation, either by scanning it with your phone or indicating in the app that you’ve applied the sensor. The CGM will then begin to collect data. Most devices have a short warm-up period (around 30-60 minutes) before the real-time data will display on your phone. 

Where do you wear a CGM? 

CGMs are designed to be discreet and worn under clothing with minimal interference to your daily life. The most common placement locations include: 

• The back of the upper arm 

• The abdomen 

• The upper buttocks area 

These areas have enough fatty tissue to enable accurate readings. 

While some CGM sensors have received approval to give accurate readings from multiple site locations like the abdomen and buttocks, others only have approval for placement on the upper arm. Check the instructions on your CGM to ensure you’re applying it in a location that will transmit accurate readings. 

The adhesive that secures the sensor to the skin is durable and water-resistant, and can withstand daily activities like showering, swimming, and exercising.

How long does a CGM stay on? 

How long you can wear a CGM depends on the device and personal preference. Most popular CGMs on the market are designed to be worn for 7 to 15 days at a time.³ Lingo lasts up to 14 days per biosensor. If your Lingo stops working before you’ve used it for the full duration, we’ll replace it (read the full Lingo sensor promise). 

Some niche CGMs can be worn for several months or up to a year at a time, but those often require a specialized application process performed by a health care provider. 

The adhesive that secures the sensor to the skin is durable and water-resistant, designed to stay attached during daily activities like showering and exercise. 

Individual factors such as sweat, friction, and skin sensitivity may impact how long the adhesive lasts for each user. Some may find the adhesive starts to peel off after a few days, while others may be able to keep them in place for the full life of the sensor.   

If you notice the adhesive peeling off sooner than you would like, it’s important to not place any stickers, patches, or tape directly over the transmitter to avoid any issues with sending the sensor data to your receiver or smartphone. However, you may place tape or other patches to reinforce the edges of the adhesive, if needed. 

How long does a CGM last? 

Check the package instructions of the CGM device you're using to learn how often you need to replace the sensor. The most common CGMs on the market have the following wear times:   

• Freestyle Libre: 14 days 

• Lingo: 14 days (read the Lingo sensor promise) 

• Dexcom G7: 10 days 

• Stelo by Dexcom: 15 days 

• Medtronic Guardian™: 7 days 

Over time, the sensor may gradually lose accuracy as it undergoes natural wear and tear. To ensure reliable readings, CGM manufacturers recommend replacing the sensor at regular intervals specified by the device instructions. 

Many CGM receivers and smartphone apps will automatically stop displaying data once the sensor has expired. By following the recommended replacement times, you can ensure you're getting the most accurate readings. 

Where can you get a CGM? 

Some CGMs, like those for diabetes patients, are only available with a prescription. Other consumer CGMs designed for people not on insulin, such as Lingo, can be purchased over the counter. Lingo is available to purchase without a prescription on our website here or on Amazon.    

A final note from Lingo 

CGMs are an established technology initially for diabetes patients that have now become increasingly popular among people looking to improve their overall health and well-being. CGMs offer a look into your unique glucose responses to food, activity, and other lifestyle habits that can empower informed decisions about your health. 

Research shows that using CGMs, such as Lingo, and limiting glucose spikes — even if you don’t have diabetes — can help improve important aspects of daily life such as sleep, mood, energy, appetite, and focus.¹

While each CGM system may have its own unique features and specifications, the overarching goal is the same: to help people explore insights into their own unique glucose data and help improve their metabolic well-being. 

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