What Causes Painful Splits On Foreskin Of A Diabetic After Having Sex?

Hi, my husband is a diabetic with celiac and suffers from psoriasis. He is also uncircumcised. After sex he sometimes gets tiny splits or paper cuts in his foreskin which are quite painful. What could this be caused from, how can it be treated so it does not return...and getting circumcised at 46 isn't an option for him he said. Thanks