"The skin rash follows a very distinctive pattern. In 3/4 of the cases, a single, isolated oval scaly patch (the "herald patch") appears on the body, particularly on the trunk, upper arms, neck, or thighs. Often, the herald patch is mistaken for ringworm (tinea corporis) or eczema. Within a week or two more pink patches will occur on the body and on the arms and legs. These patches often form a pattern over the back resembling the outline of an evergreen tree with dropping branches. Patches may also appear on the neck and, rarely, on the face. These spots usually are smaller than the "herald" patch. The rash begins to heal after 2-4 weeks and is usually gone by 6-14."
At first I didn't notice the "herald" patch until it had already started spreading. I guess it's not really caused by anything and goes away on its own, and they only treat you if you want a steroid for the itching. Mine itches, but not badly enough for me to go on a steroid. Hydrocortisone cream is good enough for me.
My entire trunk is covered now, front and back, from armpits to pelvis, and it's started on the underside of my left arm now. When I first noticed it, I had one little dry, light pink spot on my stomach. Most people probably wouldn't even notice it, but I'm so fair-skinned that everything shows up on a white backdrop.

I hope yours is just a heat rash or something that goes away relatively quickly. Maybe you should get it checked out? Hopefully it's not a poison <insert-plant-here> type thing. Good luck!
And don't scratch.....

I guess I'm having a blonde moment.