A closer look today shows that the crust is almost entirely confined to Ringo's lower lip, and hardly at all on the upper lip like I had last reported. Possibly, this condition is receding. And, since now I am seeing it mainly on the lower lip, maybe after all it is cat acne, but in the form of a crust. By the way, Raven's Mother, thank you very much for your post! I will keep examining, of course, and will post Ringo's progress here. Am still very interested to hear anyone's comments about this condition.