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You have a number of extremely good replies already; I’ll just highlight a few specific points they have already made. First, though, let me point out that there are two different kinds of scarring to consider here: The subcutaneous damage from the actual wire, and the surface irritation from the adhesive pad. Keep the issues separate in your head, or your thinking turns into “mush”.
1. subcutaneous damage.
From what I’ve read, here and elsewhere, hardly anyone has experienced IR issues with Dexcom’s Titanium-shelled wire. (“IR” == Immune Response, allergic reactions.) YMMV, but SC damage usually occurs from infection. If you feel something itchy or hurting at the wire location, rather than the adhesive pad, pull out the Sensor immediately – you probably didn’t clean the site properly, and an infection has taken hold.
Except for this risk of infections becoming more established, fewer “holes” is better (IMO). In all cases, you want to avoid irritation from the wire moving within your SC tissue- some people can use Dexcom’s adhesive pad all by itself; and others get pretty good results by “patching” loose edges with Mastisol, or similar products.
2. IR at the skin surface (reacting to the adhesive).
Others, like me, react quickly and strongly to Dexcom’s adhesive glue at the skin surface. (I react to most infusion set glues in the same way.) So for me, it’s necessary to prevent long-term contact with Dexcom’s glue first. And, as it happens, the “fixes” which I use keep the pad stuck in place forever, preventing any wire movement too.
I use “Skin-Prep” underneath, and a pre-injection cleaning procedure which many people find… excessive. Then I add a big piece of “FlexiFix” on top, which keeps the Dexcom pad edges from becoming loose over time. Some others use FlexiFix underneath, with a “Doughnut Hole” cut out of the middle for the wire injection area.
Don’t ever let the pad edges get “nasty” and loose by more than 1/8" before fixing them – or the wire starts to move, microscopically. That causes IR, and also wrecks Sensor accuracy.
I think that Richard157 and Helmut are exactly right about the main difference between pump infusion sets and Dexcom. Lisa-C is correct that YMMV, you could turn out to be less “lucky” than average. I would recommend that FHS try some of the ways which others are using to prevent to prevent both the itching and the scratching. I had actual BLISTERS from the Dexcom pad, after only 3 days, when I last did a Sensor change without Skin-Prep underneath. (I was on an out-of-town trip.)
Like many others, I use the Dexcom for 14 days. If I ran it all the way to the end of the reagent chemicals, when it looses accuracy, I would get somewhere between 16 and 19 days – but this way, I don’t risk suffering lost accuracy (from a dying Sensor) at a dangerous or inconvenient time.
Courtney and FHS: Search for “Flexifix” first. It costs a lot ($40, IIRC), but the roll is 33 feet long- so just one roll will last for years and years. To fully cover the Dexcom pad in the “long” direction, you’ll need to buy the harder-to-find 4" width. You cut off, then trim-to-fit in the narrow direction, using a piece slightly less than 3" tall. If the FlexiFix adhesive bothers you, then try Skin-Prep wipe on pads underneath everything. But remember: You need to dry it with a hair dryer, it WON’T WORK if it’s even slightly wet. (Air drying isn’t dry enough, no matter how long you wait.)