i'd recommend california baby calendula cream. very good for rashes and eczema! works wonders. you can give it a try. once, my 2nd born had very bad eczema on the cheeks. the meds and cream doctor gave didn't work. doc wanted to give steroid cream but i denied. i tried california baby calendula cream and it was gone within a week and didn't came back. same goes for my current newborn now, im using that cream. i always apply under the neck after shower, his folds, body and face! whenever he has rash or heat rash, it will clear very fast.
Actually if you read up, powder clogs their pores so I wouldn’t advise using powder. Also, when you apply powder and they sweat, it sorts of “cake” up the area just like flour + water. Keep the area cool and apply lotion after shower/wipe downs. I have been using cetaphil baby lotion since birth, baby have no rash issue. You can also try to stop lotion for a few days and use Sudocrem (apply thinly) to see if the rash and redness will go away. After the redness gets better then use lotion again.
Lucas' Papaw cream worked like a miracle for my baby.