From what I understand (I haven't used the hair dryer method yet - but probably will try it next round of rash), you just run the blow dryer on a hot setting over the rash. The principle is similar to taking very hot showers. You're putting heat on the rash to induce a reaction. From what I've read, it's pretty effective at stopping the itch at least for a few hours (or more - realize everyone is different and the reaction to these treatments tends to vary).
