more hydrocortisone, please

Let's play a game. It's called "What Is Rachel Allergic To?!"
I'll give you the first three for free: cat slobber, dust, penecillin.
Now you have to figure out the last one. I'll give you some hints. It made my hands break out in an itchy, red rash for three weeks this summer. It kept me awake at night. It isn't laundry detergent. It isn't chocolate. It isn't contagious. It came back last night and I, yet again, woke myself up itching my hands so bad they turned pink. So far it has only affected the spot between my middle fingers and pointer fingers.

OK, so what is it?! First one to figure it out wins a million dollars!