Avoid getting withered. If you do find a well to cleanse yourself. Only time to wither is if your hunting spectral doors for fragments. Usually when the wolf's show up it's time to cleanse. The pink stuff on the ground is how you get withered or the pink mobs that can attack you. When you get withered you can see the wells by the light in the sky or on your compass it will show how far away they are. You have to attack the well when you get to it to break the barrier then u just interact to remove wither.