From D&D Wiki
 Bodily Relics
 What is a Bodily Relic
Bodily Relics are various, strange things that appear in or on a person at birth. Their physical manifestation varies anywhere from a small chunk of metal that rests just beneath the persons skin, to the persons skin itself. Bodily Relics grant their possessor strange abilities that, in all logic, they shouldn't be able to grant, but they do all the same. The powers of Bodily Relics are always under research to see how they work. Bodily Relics are incredibly resilient in their pure form, being immune to nearly all kinds of alteration. Some Relics are completely immune to being affected by arcane magic, while other will never heat up, no matter the temperature of the flame they are placed in. All Bodily Relics that are in the body of a person cannot be harmed and are considered part of the person's body. Additionally, if a Bodily Relic is affected by something it doesn't have immunities to then consider it to be an appropriate substance for the purpose of hardness and hit points.
 How Bodily Relics Work
There are those who actually have learned how Bodily Relics work. These people are exceedingly rare and difficult to find, but these people have learned the way to create, or at the very least transfer, Bodily Relics from one person to another (through the Craft(Bodily Relic) skill). These methods are the only way any living being can have more than one Bodily Relic, and the method for transferring a Bodily Relic from one person to another is usually very painful, or at least trying for both people in question, requiring extremely high fortitude or will saves to keep from passing out or dying. A Bodily Relic can be transferred from a corpse who had the Relic in life to a living recipient if the transfer is made within a certain amount of time after death, depending on the Relic in question.