Now while we can see allergies, it much more common to see chronic sneezing in your kittens due to upper respiratory agents (ie herpes virus, calicivirus, etc), items caught in the nostril (less likely with the duration of her signs), and when they have nasal inflammation (if she potentially had cat flu as a very young kitten and now has scarring within the nostrils). And all of these can cause the sneezing fits we are seeing with Andy. Therefore, it is not ideal for this to be dismissed, especially if she has been sneezing for months. Therefore, you could consider videoing what she does at home for her vet to see if they are dismissing this.
Now with these potential triggers in mind, we do have a few options. First, if she came from a breeder or rescue, you can ring the organization and see if there was a cat flu outbreak when she was there. If it was and they tested, it can be of benefit to know so we can treat her effectively. Otherwise, we can have her tested by her vet.
Further to this, we can also try Andy with some supportive care. To start, if she is sneezing and congested you can take her in the bathroom while you run a hot shower. The steam will help loosen and clear some of the snot congesting her. You can also use a baby nebulizer, but often cats don’t like things held up to their faces. That said, you can alternatively make little ‘steam tents’ with her in her carrier, the nebulizer, and a bed sheet over both.
If she is building up mucus that the steam isn't shifting, use a cotton ball moistened with warm water to wipe away crust and mucus. Use saline nasal drops (like Ocean Mist) but not anything medicated. Tilt the head back and drop two to three drops in one nostril. Cats hate this, but it helps. After the drops go down, you can let the head up and wipe away any discharge that gets loosened. Then repeat with the other nostril.
If you did want to rule out allergies, you could also try her with an antihistamine. Most commonly we use Benadryl/Diphenhydramine (More Info/Dose @ http://www.petplace.com/article/drug-library/library/over-the-counter/diphenhydramine-benadryl). A low dose (ie. 0.25mg per pound of their body weight twice daily) can just be enough to reduce any allergic irritation. We like to keep the dose low, since it can cause drowsiness (just like people). And of course, this medication shouldn't be used if your wee one has any pre-existing conditions or is on any other medication without speaking to your vet first.
Finally, as herpes virus is one suspect here, you can consider supplementing her with the L-lysine. This is an OTC nutritional supplement that can reduce viral load and help them recover quicker. This is available over the counter at vets, pet stores, and even online. They come as gels, powders, and as crushable tablets that can be mixed into food. An average cat dose is 500mg a day.
Overall, her long term sneezing isn't something to be overlooked as it is not normal even if not something she shows at the vet's. Therefore, we'd have the above considerations and want to consider trying the above to help give her some relief. As well, consider speaking to your vet about testing and confirming our culprit. Also if she is very congested, they can prescribe cat safe decongestants (since human ones are toxic for kitties) and anti-inflammatories to help soothe her further and help address this for her.
All the best,
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