There could be a couple trains of thought on this. I personally wonder if it's because it speeds up the healing process to such a degree that it causes a "molting" effect on the surface where being painted.
Our new skin does grow beneath this.
I had that problem on a lesion on my arm. I kept painting the same area because of the lesion, but the entire part of my arm got very scaly and dry.
Over the course of time, what "popped" through looked
exactly, and I mean
exactly like a picture of a melanoma someone posted here. No, I never had it officially diagnosed. (I didn't want that on my medical record, and I wouldn't go with whatever the doctor would want me to do, anyway).
So, I kept painting daily and "dealt" with the scaliness. When it started to itch, I decided to use a washcloth to "drybrush" the skin before my shower, and "wetscrub" it with same washcloth in the shower. After my shower I applied vitamin E oil.
It did take 3 or 4 months total time, but you can't even
see there was
ever a lesion on my arm! I only know where this lesion was, because I treated it over the spring and summer and the skin there is not tanned as much as the rest of my arm.
Now, I know your knee doesn't have a lesion, but I felt it necessary to post my story in full. For you, the drybrushing and/or the wetbrushing and vitamin E aspect of this post may be helpful to you.
I also broke my baby toe, TWICE, this year. Nothing can be done for that. The pain was horrible - especially the second time, when I bashed my bare foot into a stool leg. I don't cry over physical pain, but I did this time.
I got the idea to paint the whole toe in iodine. (I used
this stuff). I was amazed in that the pain was literally gone within five or ten minutes.
The toe healed quite quickly. I was totally amazed!