That’s left behind by Dexcom sensors, infusion sites. I have always used goo gone and it’s worked great but my wife thinks it will give me cancer
I use Unisolve, it works great!
My Medtronic Guardian transmitter gets gooy from all the tape…if you take an alcohol swab or two and “massage” the affected area, the black stuff comes off pretty easily.
I’ve never had this problem with my sensors but baby oil usually helps remove sticky stuff.
I used tacky glue for awhile but have switched to an item called grifgrips. They do an awesome job keeping my sensors in place and will last 2-4 weeks. They are a pad that fits over your sensor and leave very little sticky residue behind. They’re great
I know this sounds funny but I just use a little olive oil which seems to break down the adhesive and I can roll/rub the black goo off. Pretty gentle on skin and I always have it around!
Unisolve is medical grade. Safe, very effective, available on Amazon