Hi.. Thanks for the query.. As per your complain it seems that the symptoms of sinus like problem or sinusitis after bringing a cat home seems to be due to ALLERGIC RHINITIS and it can be due to causes like allergic reaction to irritants like pollen, animal danders, dust and mites and at times even certain trees and grasses.. If it has happened after getting a new cat home, yes it can be due to cat danders.. I would suggest you to consult an Allergist and get evaluated and a thorough clinical evaluation and investigations like allergic tests like Patch test, RAST test, food challenge test etc can help in diagnosis and treatment can be done accordingly.. The tests will help in ruling out the exact cause of the allergen and once you know the cause of the allergic reaction you can avid exposure to it to prevent allergy attack.. You can also take anti allergics like Levocetrizine, Allegra etc along with steroid nasal sprays to relieve the symptoms.. Do steam inhalations.. You can also be instilled an Immunotherapy that will help in reducing the severity and frequency of allergic attack.. Hope this helps.. Thanks and regards.