One spotty butt cheek!!

[DidgeDoolittle]

I have just discovered that I have an acne like rash under the butt cheek of my left leg, not the right leg. It's about the size of two handspans and is technically at the top of my thigh.
I never get spots,anywhere. I have really dry skin. Where the bloody hell has this come from?
I have gone into full contortionist mode with a mirror, and discovered that it looks like acne but without any heads. There are lots of purple looking, headless spots. It doesn't itch or hurt, just looks vile.
Anyone any suggestions as to what it is and what to do with it?
I don't have any knowledge of spotty skin treatments as I usually use gooey stuff for dry skin.
All suggestions gratefully received.

[CaroleService]

I suspect it is an allergic rash (cleaner on the toilet seat, maybe?), and you should leave well alone. I bet it goes quite quickly