H-drol isnt "pretty darn close" to P-mag. I researched Pmag pretty heavily before I ran a cycle of it, and I dont remember anyone saying anything about a rash.
Rashes can be environmental. It could be a new dishwashing detergent or a new fragrance being used in the bathrooms at your workplace to a new kind of cleaner being used on the equipment at your gym. Everything can cause a rash. I wouldn't worry too much.
I am running am m1/4add P-mag stack and I had a rash for like three days. Found out it was coming from the new grips on my motorcycle. Something must have got on them, cause when I switched back to the old one, the rash disappeared!