Diaper Rash Extreme?

My friends baby is suffering from some extreme diaper rash, and it’s complicated by the fact that he’s been pooping excessively from something that he might have eaten while out with his less than savory father. So one is exacerbating the other. Any suggested remedies? If it feels anything like the abscess I had in that near region the pain he is feeling must be unbearable. I was over there tonight and this normally gleeful child is in agony. Any parents that have gone through this have any suggestions? Thanks, J.