any piercing creates a new hole in the skin. for that hole to be permanent, the hole cant be alloud to heal properly, thats why you use hydrogen peroxide so much on it, it gets rid of the crust the body makes when it trys to fix the hole.
ok, now the answer, scar tissue is what is formed when a cut couldn't heal right. thats why your ears feel a little different when you've had them pierced even though you dont have an earing inside.
you can usually tell when it's healed when you dont have any problems with it, no puss, no crust, but usually you want to wait a while before testing it
always better to have a ring in then to not