Hi there - the first question I have is this: is your cat indoor or outdoor? The reason I ask is because chronic sneezing may be caused by a herpes virus that your cat may have acquired at birth from his mom, or he may have acquired it more recently if he is outdoor. This virus is one that never will leave him, it may become latent and he will be totally normal, and then out of the blue it can flare up into a sneezing mess. Times of stress especially can cause flare-ups, but I have seen it happen for no reason at all. This is what I think is potentially going on with your cat. Is he the only cat in the household? I would recommend you try some over-the-counter L-lysine for him. The problem is that it comes in pill form and you will need to crush it into his food. You can try 500mg twice daily for a few weeks and see if it helps. If it does not help and he is deteriorating, you will need to bring him to see your vet - sometimes secondary bacterial infections can set up shop while a viral infection decreases the body's immune system. Also, you can get palatable L-lysine in a powdered form from your veterinarian. Best of luck, hope this helps!