I have No Science or education to back this up, but well before I became involved with iodine, I felt that the white pus that was a result of these initial 'red Acne bumps' were a result of white blood cells reacting to some kind of infection response. It was pure summation, but one that goes back years.
So, I find this thread really cool. To bring together ideas and expertise on this kind of topical skin response, which I have wondered about since I was a teenager.