I have a rash that itches like crazy on the back of my leg and it ONLY reappears when i'm in a certain house?

I have a rash that developed 4 years ago and totally went away after i moved to another state. everytime i come back to my old house to visit for short breaks and vactions, the rash comes back! it's in the exact same spot, and it ONLY happens when i'm back in my old house. i swear it isn't psychosomatic, because i never even think about it until it starts itching. could i be allergic to something in this house? also, it doesn't come back at a certain time of year. i visit my old house at all different times of year each year, and it ONLY comes back when i'm here. what's going on?