cfavale

Intense itch on left upper arm. No rash but after scratching little red marks appear and could bleed due to scratching. Arm becomes very hot and red. I use Benadryl - oral and gel - to relieve the itch. Takes a while for the itch to subside and as long as I don't touch my arm or move it tends to stop. However, it does come back maybe the same day or the next day. It seems to be ongoing.
I don't understand why one part of the arm itches and what causes it. I have been to a dermatologist and she didn't seem to know what causes this. She gave me medication - topical cream - which seems to work. I would like to know what causes this.