Why Was Cauterization Done Causing Pain And Stinging?

I am 64 yr old female with a pessary for prolapse and an estrogen ring . During a routine removal, Refill of the ring and cleansing of pessary, after all was done, the DR, ( not my regular) as I am away from home, said I had an irritation , or cut externally and a minute later cauterized it. WHY? I was caught off guard and don't know why. It hurt, and stung. What was this for?