I hear woods and well demarcated, spreading, pruritic rash and I think poison ivy
Another way to get there: here's no fever but he is v v itchy, so think type IV HSR
Abrupt, sharp line of demarcation, no systemic signs, and mention of environmental exposure should make you think less of strep skin infections
So we're thinking some contact in the forest and we're back at poison ivy or some other allergen
Can treat with antihistamine, but what about prevention? Avoid the woods.
Google bullous poison ivy