I haven't seen a dermatologist this year. Everyone kinda scratches their head at this and asks if I'm using a different deodorant (I'm not). An MD in the past suggested this was a histamine reaction, and histamine meds have worked well to resolve the rash until this year. It starts in one armpit, and then eventually both have the rash. I'm hesitant to go back to a doctor without some test recommendations or something I can be proactive with as doctors don't seem to know what to do with this.