Lycanthropy

Lycanthropy is a magical curse, which causes it's victim to slowly take on features of a beast. Which beast depends on the type of lycanthropy the victim is cursed with. A lycanthrope can turn into their beast form at-will, but are forced to do so when hit with the light of a full moon.   Lycanthropes are immune against non-magical damage, and damage applied by non-silver weapons.  

Silver

Contrary to popular belief, a lycanthrope can touch silver without any issues. However, when the silver comes in contact with any of the muccous membranes (mouth, eyes, inside of the nose, etc.) or get's through their skin, it will do them harm.   Blunt-force trauma applied by a silver weapon is also harmful to a lycanthrope. The exact mechanism is unknown, but if a weapon would harm the lycanthrope, and there is silver within 1 inch of the location of that harmfull effect, the harm is indeed applied.