A friend of mine’s cat does a less aggressive but similar thing. They now have a ritual every morning and every night, where she gets out a paper towel, the cat jumps into her lap, and she rubs/scrubs away at her ears for a few minutes. My assumption is that my friend’s cat has a mild allergy of some kind.

Assuming that it is an allergy: My personal philosophy on this sort of thing is that I’d rather prevent / minimize the allergen from reaching the cat, rather than letting the allergen reach the car and then treat the symptoms: allergic reactions cause inflammation, which can increase your risk of other health issues later on.

My personal suggestions, in the order I’d make them, due to the effort or side effects involved:

1. I’d try gently rubbing the inside of your cat’s ears once or twice a day, maybe with a tissue or paper towel. Hopefully this will help reduce her desire to scratch while you’re working on diagnosis.

2. Cats can be allergic to their litter, particularly the dust, clumping agents, or fragrances. Don’t switch to a corn-litter, as that’s a common-ish food allergy in cats, plus if you have one allergy, you’re likely to have others. There are litters marketed as hypoallergenic, but I’m not sure how truthful those claims are. You’re looking for one with no fragrances, no clumping agents (an older-style fragrance-free clay litter might work), and minimal dust. Note that some cats get annoyed at litter changes, so you may need to mix old and new litter in increasing percentages over like a week for her to accept the new litter. Once it’s full switched, give that a couple weeks and see what happens.

3. If the litter-change doesn’t work, try transitioning your cat (transition over a week or so to avoid stomach upset) to a hypoallergenic cat food. Give it a couple weeks and see if things are better. If it is, then it’s likely some kind of food allergy; you can look over the ingredients between the hypoallergenic food and her regular food, to try to determine what she’s allergic to so that you can switch her to a less expensive or more readily available food. [You’ll want to check wet food, dry food, and all treats.]

4. If it’s not a food allergy, it could be an environmental allergy (the litter is an environmental allergy, but it’s also the easiest thing to change). Does the problem get better and worse at different times of year? In that case, it might be something like a pollen allergy (indoor cars can also have pollen allergies). You can get the cat tested for those, not I’m not sure it’s worth it because I’m not sure what the allergist would recommend. My suggestion would be to vacuum and dust the house thoroughly, especially the areas where the cat spends much of her time to get rid of any allergens currently present. This does include things like cat trees, cat beds (wash it if possible), etc. Once that’s done, I’d put pillowcases or similar small pieces of cloth in her favorite nesting places, and wash those weekly using a fragrance-free laundry soap. I’d install HEPA filters on your HVAC system, and consider one of those room-purifying air circulator units if needed. Doing one thorough cleaning, putting down a washable barrier layer that gets washed regularly, and limiting pollens getting into the house should significantly reduce environmental exposure, particularly if she’s an indoor cat.

I agree that Benadryl is an option, but I’m leaning against it being your first option because it doesn’t work in all cats and, like I said, I prefer addressing the cause and not the symptom. But if it is an allergen and you can’t figure out the root cause, then Benadryl may be your best option. If you go the Benadryl route, check with your vet for dosing, frequency, safety and side effects (or they may have a recommendation for another allergy medication as well).

Good luck, and please let us know how you get on!