How old is Marlowe? He may be reacting to the change of season, or the bad thing is they can develop allergies to specific foods over time. Yes you can use that on the raw irritated stain.
I myself have been trying the malecitic ultra, seems to be working really well on the couple of difficult stains I had going on here. You may want to just apply some desitin or anti fungal cream on the wrinkles to calm them down for a few days before using anything else, if they are red and enflamed it will soothe them very quickly.