This is one therapy that should not be performed by amateurs — you should think of it as a medical procedure. It’s not appropriate for everyone, or every condition, and certified practitioners know exactly where to apply pressure for different issues as well as exactly when to stop. Without a licensed professional, you could wind up with actual bruises or tissue damage. Also by bringing blood up to the surface, you risk passing on blood-born infections so proper hygiene and safety precautions are essential.
