Keep your baby's diaper area clean, cool and dry. Wash baby’s bottom every nappy change with water. No need for soap. I only use soap when my baby poops. No powder too for Talcum powder can get in my baby's lungs. Cornstarch may make a diaper rash caused by a yeast infection worse. Pat dry (not scrub, it can irritate your baby's sensitive skin) to dry completely before putting on another diaper. Avoid baby wipes, it’ll save your baby’s delicate skin from irritation and even your pocket.
If your baby has rashes, try applying Desitin, Drapolene or Petroleum Jelly liberally to the affected area. If diaper rash persists, change the type of wipes, diapers or soap you're using.