I spent the entire fall and early winter trying to cure what I thought was DH. Tried low iodine, went crazy trying to locate hidden gluten in my life... turns out the "rash" was bedbug bites! Just sharing this because they are apparently epidemic, and the bites really looked and felt much like all the descriptions of DH that I have read, so if anyone thinks they have DH when you never have before - it might be worth looking into. Disgusting and embarrassing, but at least treatable.
And you can have them even if your house is very clean (mine is!). They don't like filth - not like roaches - what they like is blood, so if you have blood, you can have bedbugs.