Here is a site that goes into it a bit.
www.newadvent.org...
Mystical Stigmata
To decide merely the facts without deciding whether or not they may be explained by supernatural causes, history tells us that many ecstatics bear on hands, feet, side, or brow the marks of the Passion of Christ with corresponding and intense sufferings. These are called visible stigmata. Others only have the sufferings, without any outward marks, and these phenomena are called invisible stigmata.



