Hi I hope my reply can help you and your cat. My persian had the same swollen lip it took me month of vet visits and costs just to be referred to a dermatologist who want nearly $700 to find the "allergy" that was causing the swelling aka (eosiniphilic granuloma). My cat was placed on steroids which would temporarily help with the swelling but then it would return. I spent so many hours trying to get to the bottom of this and I came across a study where ZYRTEC was used at 5mg dosages daily to control this condition. It has worked wonders on my cat and I hope it does the same for yours. ZYRTEC is used on humans as an allergy suppressant and works safely on cats as well.