I’m with Helmut and Dave on using Mastisol, when the edges start to go. But for me, unlike Dave, that’s all the way up to about day 12. I’ll guess that it’s because I use Smith and Nephew “Skin-Prep” wipes first, and he doesn’t. Dave, am I right about that guess?
Anyway, these wipes are NOT! the same thing as the “I.V. Prep” wipes- they’re specifically intended for helping appliance adhesion, and “reducing the risk of tape stripping”. Coat once, wait to dry, then re-coat again with just one extra swipe, and wait to dry COMPLETELY before setting the Sensor pad on the area. (If you live in a place with humidity, a hair dryer on “low” can speed the waiting a lot.) You don’t have to leave a doughnut hole for the Sensor wire, just wipe the entire Sensor pad target area.
As with Mastisol, if you press the Dexcom tape on to your skin before the liquid has completely dried, it won’t work correctly. That’s the most common mistake people make with Mastisol. Here’s the right way:
First, you need to buy the non-spray bottle-- you need to drip Mastisol onto Q-tips for control, rather than spray it all over the place. When the tape has failed by about 1/8" inch, Grab 3 Q-tips. (Don’t wait any longer than 1/8" of peeling.) Dip one end of the first q-tip, and use it to roll the failing portion of the Sensor tape up and AWAY from your skin, towards the Sensor housing. This rolling-up action will pull away a bit more “nearly failed” tape at the edges of the total failure area, that’s good. (Stop pushing at it when you reach the still-attached portion.) Then, if the Q-tip is still pretty clean, use it to clean old adhesive gunk off your skin, coating your skin with Mastisol at the same time. If it’s already dirty, use a second Q-tip, freshly dripped. All of Dexcom’s “black goo” needs to be removed; extra time, rather than extra scrubbing, does the job best. (Note that using Q-Tips helps to keep the skin and adhesive pad apart while you’re working on either surface, that’s key.)
Now wait for at least 40 seconds. Just like “contact cement” wood glue, it MUST be dry before you stick the surfaces together! Using a dry Q-tip (probably the 3rd one use in the job), roll the edges of the pad back down onto your skin. Don’t press with your fingers-- the rolling action is better, because it spreads out semi-wet adhesive “lumps” without distorting the fabric. It also keeps Mastisol off your fingers, that’s nice too.
For me, that one fix-up lasts until the Sensor dies. And, back on the original STS, I usually got 17-19 days. I get a few days less with the 7+, but Mastisol seems to hold up for a lot of people-- if you do it right. YMMV, of course.
BTW, that “Skin-Prep” stuff creates much less redness on my skin than “I.V. Prep” did, and because it coats your skin, it’s also acting as a partial barrier against reactions to the Dexcom pad adhesive.