What can I do about drool rash?

Bibs+Cortisone cream. Since you can't stop a baby from drooling, keeping the skin dry with frequent bib changes is the best prevention. The rash is a form of contact dermatitis and can be safely and easily treated with twice a day cortisone cream for 1 week. If this does not help, please have the rash checked by your pediatrician.
Aquaphor or Vasoline. Drool rash is very common in children. It may worsen during teething (when your baby tends to drool more) or during feeding. Typically using a barrier lotion/cream such as aquaphor or vasoline will protect the skin from the drool and the irritation will decrease. If your baby's rash begins to look more yellow and crusty see a pediatrician as your baby may have developed a secondary infection.