Your symptoms sound exactly like mine when I had an allergic reaction to Alleve, the pain killer. My boyfriend can take handfulls of it but not me. Skin became tight and leathery all over and, at one point, I couldn't bend my fingers. Bottom line, I'm guessing its not that Simple Green is caustic, per se, but that you're allergic to something in it or, perhaps, some thing new you may have taken. Hope it goes away quickly!!