Heat rash?

Hello mommies. My lo is 4 weeks old and the rashes on his cheek is getting worse day by day. It all started with few little bumps initially but now spread all over chin. I googled and saw treatment for heat rash is to let the skin just like that but paed advised to apply cetaphil. What to do to prevent this heat rash? Please advise. #heatrash #newborn