your question is answered on this forum; scroll down and you will find it. bottom line, it's not a good idea.
What would happen if i gave my fiancee oral sex whilst having a cold sore ???
Ed:
Recurrent cold sores are always outside the mouth, at the lip margin. Canker sores, pssibly viral but not herpes, are inside the mouth but sore. They're not contagious. I'm not sure if the white spot in your wife's mouth is even a canker, but it almost surely isn't herpes. A doctor seeing it when it's there would know for sure.
Best.
Dr. R