My son has had a terrible rash around his anus off and on for months. He has had a strep test, which was negative, treated for yeast with Nystatin with no improvement, been treated with hydrocortisone and also silver sulfanide. The silver helps temporarily, but after a week or so, it blossoms in to another rash. He has also had a blood test for allergies, which was negative. I don t know what else it could be.