There are certain bacterias in the anus hole that dont belong in the cunthole. Some of those bacterias may cause the pH balance in the crotch hole to go awol, and/or form a yeast infection, even a bacteria infection such as bacteria vaginosis. There are multiple possibilities.

Your mouth hole and cunt hole are similar pH than the brown cave and the cooter. Just think of it as oil and water. They dont friggin mix.

Suckage I know.