I've had this before!! I actually don't know what it is, my mom thought it was an allergic reaction to the adhesive, but we're both not entirely sure. Try not to touch it or itch it, the way I prevented this is using nasal spray around the area you plan to put the adhesive on! It worked immediately and after a while of using it, I didn't need it anymore!! Just don't itch it, trust me!!

I get this every time due to intolerance to latex and adhesives

Yeah, I had to wear medical tape on the same bits of skin for two months last fall when I got badly burned. The adhesive tugs on the skin and irritates it, so after multiple days it causes dermatitis. Definitely don't itch it and be super gentle with the skin, if it's irritated it can start weeping like an open wound. Ice packs and allergy medicine help a ton with the discomfort! Cold feels sooooo good!!! Having fans blowing on my skin helped me sleep with the itchiness. Anti-itch cream helps too but try to avoid ones with hydrocortisone. If you start getting full body hives or red streaks in your skin around the cannula site or pus that's all signs of things that need medical attention.

I'm allergic to the dye used for MRI scans. The cannula itself is not a problem. The tape causes irritation and a rash but the dye used for contrast in the scan causes a more severe reaction for me. I get swelling, itching and hives all over.