Barrier creams are used as a preventative measure, so once nappy rash hits, you need to look to other solutions. One of the best options is exposing baby's bottom to the air, frequent nappy changes and generally keeping the skin dry. However there are products available to buy from all good retailers and pharmacies that treat this condition, one of which is Metanium.
Metanium Nappy Rash Ointment is a medicine. Always read the label.