M.D.
Yes, diaper rashes can be caused by yeast, regardless of whether or not the baby has oral thrush. My baby's worse diaper rash was caused by yeast and went away quickly when treated for it. His most persistent diaper rash was caused by a cow's milk intolerance and only went away when I cut dairy from my diet (I was nursing) - something to keep in mind if an antifungal for the yeast doesn't help.