The rash hurts more than it itches. It feels like a very bad sunburn and is very hot to the touch. It's really sensitive; showering was quite painful for about a week when I had it.

It did start as a small itchy area and I (stupidly) paid no attention and took another dose so that I woke up with my face a mess that kept getting worse, but honestly it is so specific looking and feeling that if you really have THE RASH I think you'd know it.

However you can get other rashes coincidentally and those still need checked out so it's good to pay attention but basically your body will tell you if you really need to worry, at least in my experience.