When I shower, I break out in red “bumps” across my chest, abdomen, shoulders, and back?

When I shower, I break out in red “bumps” across my chest, abdomen, shoulders, and back. I also noticed this after I went for a run outside with no shirt. At first, it was just a small patch, and it did not itch, burn, or anything, so for a while I was not concerned; now it is spreading all over my upper body.