I just wanted to share my experiences with feline acne. After MUCH experimentation we finally have it under control.
We have two cats. The eldest gets very bad cat acne (blackheads and deep, huge white cysts). We tried everything from homeopathics to topically applying castor oil, oregano oil, aloe gel, apple cider vinegar, colloidal silver, rubbing alcohol or hydrogen peroxide (which both seem to work great at first but then cause terrible rebounds), switching to metal and/or ceramic bowls... and I'm sure other things I can't think of right now.
This is what seems to work. For our older cat it is a management system that requires light cleaning most days (at least checking so any breakouts can be nipped in the bud). Our younger cat has started to have the same problem- at about the same age as the other one began to have issues. But the younger cat only needs a treatment if it flares up and then he'll be fine for quite a while (months). So, I think each cat will differ in terms of frequency of treatment.
I'll start with diet, which has helped but hasn't been a cure. I add 1/3 of a can of wet food (we like the organic kinds) to about two cups of dry food (Iams). I then add a heavy dash of turmeric and two capfuls of apple cider vinegar, 1/3 dropper of oregano oil, and the same of colloidal silver. I add a little water and mix it all up really well. This lasts two cats a few days. (And they love it!)
For breakouts we have a cleaning routine. I find it easiest to sit on the floor with my knees together and bent and feet on the floor. I put the cat face up so he's cradled in my legs (head at my knees) and I can easily hold him and his head (firmly). Even the younger scaredy-cat puts up with this once I get him situated. Then I clean the skin thoroughly with a Q-tip (or multiple Q-tips) saturated with colloidal copper. For some reason this has turned out to be the best cleanser. With the younger cat any little white cysts are easily removed with just the Q-tip. The older one sometimes needs cysts and/or blackheads expressed (popped) so that he can get back to healing. I clean it until all dirty looking crumbs/residue is gone. Then, if it's an acute attack, a dab of Neosporin antibiotic ointment rubbed in well to the fur/skin. And that's it. We tried so many natural treatments, but antibiotic ointment is what really stops bad outbreaks in their tracks.
I have also found that ingesting oils or petroleum products (as in hairball goo) definitely cause breakouts. Also, adding things like vitamin powder to the food does too (it collects under the chin and they can't clean it). We also tried adding sage extract, CoQ10, and MSM to their food at intervals which did not affect outbreaks one way or the other.
If anyone ever finds a true CURE, we'd love to hear about it! Until then this management system works pretty well for us. The older cat finally has full chin of healthy hair again and no current acne!