Bull's Eye Rash of Lyme Disease

[n1person]

Recently I had Lyme disease and had perhaps the most stereotypical bull's eye rash ever. All medical people I met wanted to see it, and called their friends/coworkers over, took pictures, etc.

But the rash still has me confused about the biology of it. The shape itself doesn't seem to make biological sense to me; why is there a white ring that is unaffected by whatever bacteria is there? Why does the rash occur at a different place than the tick bite?

Thanks for your help!

[AyazM]

This is erythema chronicum migrans. I knew of the reason for that bulls-eye appearance but now that I have forgotten, I can't seem to find on internet where I read it.

Can some dermatologist, or microbiologist help us here find the reason?