It is more likely to occur on the neck and upper chest, in the groin, under the breasts, and in elbow creases. Adults usually develop heat rash
in skin folds and wherever clothing causes friction. Heat rash
looks like a red cluster of pimples or small blisters that maybe associated with itching. Most often, heat rash goes away on its own. Severe forms of heat rash may need medical care, but the best way to relieve symptoms is to cool and dry your skin and prevent sweating.
I hope this helps.