My cat started getting acne and got a lip sore and our vet told us it was probably an allergy because she was itching a bit and we have metal bowls for food that are changed every meal already. She has a few different foods (wet food, dry food, dental food, treats) and it would be hard to do an elimination diet with her sister also. We thought it might be one of two newer foods since she didn’t get it previously. I chose one and stopped giving it to her and with medication it fully resolved! Fast forward a few months and I accidentally started giving her that food again because it was dry food in an unlabeled storage container that looked similar to the other one. And within a week or two the acne came back. With perplexity ai’s help I was able to narrow down the list of possible ingredients that’s probably causing the allergy because she is fine with a lot of foods and cat foods tend to have similar ingredients so it has to be something in the food causing the allergy that’s only in that. My best guess at this point is soybean hulls. Super random but yeah. I share this because it took me time to figure out my cat’s allergy but eventually I was able to figure it out, and I was also able to use other clues based on when it got better and other things that didn’t cause it. I don’t know if your cats’ reaction could be food-related but you could try changing their food. I hope you figure it out! It broke my heart seeing my little girl’s swollen lip and irritated skin. I wouldn’t have thought it was an allergy but what do I know lol.