It can be an allergic reaction, viral rash or heat rash. Use a mild cleanser with moisturizing properties like Cetaphil. Also use cotton clothes and change the clothes twice if there is any increased sweating. Try keeping the skin free of sweat as far as possible. If the symptoms still persist then you can apply mild steroid. For the itching antihistaminics like Benadryl or Claritin can be taken.
If the symptoms persist then please consult a dermatologist and get it examined.
I hope it helps. Take care and regards.
Sounds like an allergic reaction. Have you eaten anything out of the ordinary or used any new lotion or cream? A change in diet is usually the cause of my breakouts-- and I normally have very balanced skin as well. Usually the culprit is too many oily foods one week or taking too many oily supplements/vitamins that throw my pH off balance.
Also overwashing/scrubbing skin can take off the protective layer, exposing your pores to bacteria and causing breakouts. This is another issue I've experienced myself.
Do some brainstorming and cut back on whatever you suspect might be the cause.
You will figure it out, I promise!
All the best.