These are great photos, thanks. Two possibilities come to mind. First, some people are just more susceptible to skin bends for reasons that aren't clear. Second, the rash (at least from what I can see on the photos) could also be consistent with cold-induced urticaria. If that's what it is, you can duplicate it by placing an bag of ice on your abdomen for about 5 minutes. If you try that and the rash doesn't appear, I'd recommend you seek out a UKDMC diving medical referee for an opinion if you haven't already done so.See attached two pictures.
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This was taken in October 2023, around 3 hours after the last dive. I noticed itching probably after 2 hours or so but completely disregarded it initially. It responded well to 100% oxygen and almost disappeared the next day. Irresponsibly, I did a shallow dive (15m) after around 24 hours on Nitrox 28%. It got a bit more colour again but then it completely vanished over the next 5 days and never got that bad again during those 5 days, even though I did a few more shallow dives on Nitrox in the next few days before the trip ended.
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This one was taken last Saturday at A&E. I noticed the itching an hour after the dive and immediately realised what it was, got 100% oxygen right away. I arrived at the A&E in the next 30-40 minutes when this was taken by my doctor.
Best regards,
DDM