What Causes Blisters On The Surgical Scar Post Application Of Garlic?

I put raw garlic on a metal plate leg surgery scar which has been healing for 6 months. It was put on where there was a bump of infection. what can happen? It was left on for approx. 9 hours. and burned too much because of the sulfur in the garlic there are blisters and I thought they were there from the heat but also the infection coming out.