Heat rash looks like tiny
bumps surrounded by a zone of
red skin. Excessive perspiration damages cells
on the surface of the skin, forming a barrier and trapping sweat beneath the skin, where it builds up, causing the characteristic bumps. It usually occurs on clothed parts of the body, such as the back, shoulder, abdomen, neck, upper chest, groin, or armpits and goes away on its own within a few days.
I hope this helps. Take care and keep us posted.