Applying a FreeStyle Libre 3 sensor takes about a minute once you know the steps. The sensor goes exclusively on the back of your upper arm, sits flush against the skin, and lasts up to 14 days before you replace it. Getting the preparation right makes the difference between a sensor that stays put for the full two weeks and one that peels off early or gives unreliable readings.
Choose the Right Spot on Your Arm
The only approved location for the Libre 3 is the back of your upper arm. Placing it anywhere else can produce inaccurate glucose readings. Within that area, pick a spot that stays relatively flat during your normal movements, avoiding skin that folds or bunches when you bend your arm.
Stay at least 1 inch (2.5 cm) away from any insulin injection site. Avoid areas with scars, moles, stretch marks, or lumps, as these can interfere with the tiny filament that sits just under the skin. If you’re replacing an old sensor, rotate to a different spot on the same arm or switch arms entirely. Using the same patch of skin back to back increases your chances of irritation.
Prepare Your Skin
Proper skin prep is the single biggest factor in keeping your sensor attached for the full 14 days. Abbott recommends a three-step process: wash, clean, dry.
- Wash the application area with a non-moisturizing, fragrance-free soap. Moisturizers and fragrances leave a film on the skin that weakens the adhesive bond.
- Clean the area with the alcohol wipe included in the sensor kit. This removes any remaining oily residue.
- Dry your skin completely before applying the sensor. Even slight dampness can prevent the adhesive from gripping properly. Give it a full minute or two after wiping with alcohol.
If you’ve had trouble with sensors falling off in the past, you can apply a skin prep product before placing the sensor. Skin-Prep Protective Wipes from Smith & Nephew or 3M’s Cavilon No Sting Barrier Film are two options that Abbott lists as compatible. These create a thin layer that helps adhesives stick while also protecting your skin from irritation. Apply the barrier product first, let it dry completely, then place the sensor on top.
Apply the Sensor Step by Step
Each Libre 3 sensor kit comes with a sensor pack and a separate applicator. Here’s the process:
Wash your hands before handling anything. Open the sensor pack and unscrew the cap from the sensor applicator. Place the cap on a flat surface with the dark circle facing up, then press the applicator down into the cap until it clicks. This loads the sensor onto the applicator. You’ll see the sensor is now attached and ready.
Hold the applicator against the spot you prepared on the back of your upper arm. Press down firmly. You’ll feel a quick pinch as the applicator inserts a thin, flexible filament about 5 mm (roughly a fifth of an inch) under your skin. This filament is what measures your glucose levels. The insertion takes a fraction of a second, and most people describe the sensation as less painful than a standard finger prick.
Gently pull the applicator away. The sensor should now be sitting flat against your skin with the adhesive pad secured around it. Run your finger around the edges of the adhesive to press it down and ensure a solid seal. Dispose of the applicator, which contains the used insertion needle, in a sharps container.
Start the Sensor With Your Phone
Once the sensor is physically attached, open the FreeStyle Libre 3 app on your phone. Follow the prompts to scan or pair with the new sensor. The sensor needs a warmup period of about 60 minutes before it begins delivering glucose readings. During this time, it’s calibrating to your body’s interstitial fluid. You won’t get any data until warmup is complete, so don’t worry if the app shows a waiting screen.
After warmup, the Libre 3 automatically sends glucose readings to your phone every minute without scanning. This is a change from earlier Libre models that required you to hold your phone near the sensor.
What to Do if You See Bleeding
The filament occasionally nicks a tiny blood vessel during insertion. A small amount of bleeding at the application site is normal and usually stops on its own. You don’t need to remove the sensor. Just apply gentle pressure with a clean tissue and give it a few minutes. If the bleeding doesn’t stop, remove the sensor and reach out to your healthcare provider.
Keeping the Sensor On for 14 Days
The Libre 3 is water-resistant and rated for submersion in up to 1 meter (about 3 feet) of water for up to 30 minutes. That means showers, baths, and casual swimming are fine. Deep diving or extended time in a pool can exceed those limits and compromise the sensor or its adhesive.
If you find the edges starting to peel after several days, over-patches can help. Abbott sells its own adhesive patches, and many third-party options exist. Apply the patch over the sensor, leaving the center clear so the sensor itself isn’t compressed. Avoid wrapping the area with tight bandages that could shift the sensor’s position.
Sweat, humidity, and physical activity all test the adhesive. If you’re active or live in a warm climate, the skin prep step becomes even more important. Some people find that applying a skin barrier wipe before every new sensor eliminates the peeling problem entirely.
MRI, CT Scans, and Other Procedures
You can keep your Libre 3 sensor on during CT scans and MRI exams (both 1.5T and 3T). The sensor has been FDA-cleared for wear during these imaging procedures, and it doesn’t need to be removed beforehand. During an active MRI scan, your readings may be temporarily inaccurate, but the sensor returns to normal operation within an hour after the scan. Leave your phone and any reader device outside the MRI room.
The one exception is diathermy, a type of therapy that uses high-frequency electrical heat. Remove your sensor before any diathermy treatment. The heat exposure can damage the sensor and produce unreliable readings.
Removing the Old Sensor
After 14 days, the sensor stops collecting data and your app will prompt you to replace it. To remove, simply peel the adhesive pad away from your skin. Pulling slowly and steadily at a low angle, close to the skin’s surface, is more comfortable than ripping it off quickly. If adhesive residue remains, a small amount of baby oil or adhesive remover will take care of it. Dispose of the used sensor according to your local guidelines for medical waste.