That's very interesting, MH, and something I would never have thought of on my own.
I've always had sensitive skin. I'm using the B&W on the areas I'm experimenting with the Black Salve (I'm sending you an e-mail later about this with some pictures.) You can tell exactly where I've put the B&W because the skin is pink, not flesh colored. I always apply from the outside in toward the center, so I know I don't get any of the black salve beyond where I want it. It is definitely a reaction to the B&W, but doesn't hurt or bother me in any way.
I will definitely try to increase my iron. Do you have any suggestions? Eat more spinach in my salads? Or could it be too much iron? How would I know?