Hello,
There are many possibilities for such a rash like allergic reaction, fungal rashes, shingles rash, viral rashes, heat rash, sweat dermatitis or pityriasis rosea. To confirm the diagnosis, please get an evaluation done from a dermatologist as treatment for all is entirely different.
I hope it helps. Take care and regards.
Could be a number of things. Can certainly help if you can send me some pics