Should your cat experience an allergy to lavender, your veterinarian may recommend shampoo or ointment that contains hydrocortisone. These will help with the swelling and skin irritation that your cat is experiencing. Antihistamines do not work to alleviate symptoms in all cats, however, they are an easy option to try in order to help your cat get relief. Corticosteroids are typically very effective in reducing the allergy symptoms, although they do cause serious side effects (particularly when used over the long term) and are usually only recommended as a treatment upon other options not being successful. Should your veterinarian recommend corticosteroids, side effects in short term treatment tend to be minimal (diarrhea, increased thirst). Long term use of corticosteroids can lead to your cat developing problems with his liver as well as diabetes. When your cat is being treated with corticosteroids, your veterinarian will likely monitor his blood chemistry levels in order to catch any problems as they develop.
Another treatment your veterinarian may consider should your cat be experiencing an allergy for an extended period of time and is not responding to antihistamines is immunotherapy. Immunotherapy takes a lot of time to develop and is costly, however it is very successful. A test will be conducted that will confirm the active allergen and then an injection will be developed specifically for your cat with altered antigens. The injection will be given weekly or monthly which will lead to your cat being desensitized to the allergen.