Mask

Masks where used in rapture during the celebration of the New year of 1959. during and after the civil war masks where worn to hide the cosmetically side effect of splicing. The most iconical one is the Bunny Mask

BioShock
Masks are worn by the Splicers to hide there facial deformities.

BioShock 2
8 Years after the events of BioShock. masks are still worn by splicers to hide there even more deformed faces. some of the masks have taken some damage under the time.

BioShock 2 Multiplater
Masks are also used in BioShock 2 Multiplayer by the playable splicers. you start of with a few masks, by ranking up you earn more masks. there is 15 different masks