(Sorry to hear about the itch, but search this forum it has been discussed before, hopefully you’ll find answers, I’m not familiar with the topic).
In my case it was not the caffeine which was the issue
I thought the cafe made coffee similar to me, coffee plus water plus a bit of milk on top. Wrong. Their’s is 90% milk. It’s really a glass of milk with a bit of coffee floating about!
I did this for 4-6 weeks, no problem. I must’ve scraped it into keto land somehow but eventually it did catch up with me and throw me out of keto. I use a blood analyser and got 0.2 mM.
So I’d question not the caffeine but “what else” is in that mug?