I had so much happening that it was quite impossible to figure it out before and now, as a fading remnant for me, it might be possible. Keep a daily diary of skin, other symptoms that come and go. What other symptoms show up the days before or few days after. It may be very subtle. If you can find what sets it off, ie if it happens with other symptoms, it could be another induced deficiency. I have speculated that it is replacing damaged deeper tissue that didn't form correctly at the time. I would get all the deadlock quartet going, get rid of as many symptoms as possible and see what emerges at low tide as it were, keeping a daily diary of all the details. That is how I have gone about tracking down all sorts of things. I have called it "high resolution symptom tracking" to separate it from the hyper attentive to changes for which docs will kick you out of the practice or give zero credibility. I have tracked down half a dozen things that happened; each 2 weeks, each 10 days, each week, each 24 hours. It turned out that they were the intervals between certain things. It's a lot of tedious work but it is the only way to see the subtle patterns that are solvable but nobody can do it for somebody else. Or for a familiar quote "Insufficient Data" to solve the problem.