I had got a small dark patch on my lower back quite a while back. It used to itch a lot and now because of my itchin it has become a big dark patch and the outer layer is swollen and itches all the while. What is it?

I had got a small dark patch on my lower back quite a while back. It used to itch alot and now because of my itchin it has become a big dark patch and the outer layer is swollen and itches all the while. What is it?

It could be a fungus , could be allergies, have you seen a doctor?