Barbe had chronic cat acne for years, and I tried various treatments over time, including my vets recommendations and many suggestions from this site (incl the apple cidar vinegar, Vetericyn and colloidal copper, just to name a few). She always had a porcelain bowl, and I got into a habit of cleaning the edge with a water & bleach solution, in addition to various treatments, with no significant or lasting improvement. She hated the daily cleansings and different treatments rubbed into her chin, altho we tried doing it different ways and I always rewarded her afterwards. I had also tried adding calming ingredients, like valerian, because I associated her acne with her anxiety & fearfulness. But then I gave up because it was like torturing her, and for no benefit! I was doing absolutely nothing for a few months since nothing seemed to help.
For a separate reason involving my elder dog's health, I then began supplementing my dog & cats meals with a meat & veggie mix which I made myself. I settled on using a canned pumpkin base then processed in fresh baby spinach. I often add a very small portion of other things (from my meals) like a couple slices of raw zucchini, or a few pieces of the soft insides of broccoli stalks, and cooked green beans or carrots. I process that together, sometimes adding low sodium chicken broth to make it easy to spoon, then stir in either canned chicken or canned salmon.
I give them each a spoonful with meals for 4-5 days out of the week, along with their dry food mixes of Instinct & Iams. They all love it! Before that, Barbe usually refused anything but dry food and select meats, often even turning up her nose at things like canned cat foods and Instinct's frozen raw mix. She has always been the pickiest of eaters, but she liked the veggie mix, altho often waits until I put the dry food on top first to get her started.
After about 6-8 weeks of supplementing, I was surprised to see -- for the first time -- her chin was clear, without any signs of the usual acne. It has remained clear for weeks, and I've noticed that her personality is noticeably less timid, she doesn't want to isolate in a separate room as much as she used to, and she's clearly happier and more playful with the other cats! I am thrilled that I found an easy cure that doesn't involve touching her chin -- all I do differently is feed her something she loves.