They say 25% of people are not affected by it, 25% are very sensitive (me), and 50% are in between. One year I cleared my 350 foot stone wall of brush, wore gloves and long pants and a long sleeves shirt and still blew up like a balloon.
I used to always get them at my old house under the south facing shutters. You could them scratching if you were inside the rooms with shutters. Plus I saw their poop on the ground.