I've had the same thing for about 10 years now, when i exercise or when i'm exposed to extreme heat and a lot of sweat i get a rash, pimples concentrated in an area. Mine is on my chest, neck, back, chin. it normally starts on my chest and i can see red bumps when it's really hot and if i don't take quick showers it grows to my neck and back and it keeps going up the longer i stay in the sun and sweating. I've been to the doctor a few times and the only thing that has helped is to take quick showers every few minutes. I know it's not easy to do sometimes but for example when i go to the beach i go to the public shower and just rinse the sweat off, same thing when i'm playing sports, every hour or so i go and take a quick shower. It always works. What sucks is when i'm at places when i cannot take showers like last week, I went to the football game and it was hot as hell outside but I couldn't take showers and now i'm paying for it, my chest and neck is all broken out.
I have had the same problem with breaking out with a rash. It started about 10 years ago in my first trimester when I was pregnant.
I find the only thing that works is baby sunblock. The spray type but this only helps keep the rash at bay on my hands and arms. Also when I wear tight jeans then I notice a break out.
Try to wear loose cottony clothing that allows the skin to breath. Using a special type soap also helps that is for sensitive skin.
You are so full of c**p.
I wish we could figure out how to stop this, I am tired of looking like I don't bathe for half the year.