Some roles with a lot of cinematic history behind them are: the disfigured victim; the scarred and vengeful villainess; and the heroine who is almost miraculously transformed into a beauty (often with disturbing side-effects). And, of course, the more beautiful the actress behind the makeup the more shocking the transformation.
Skinema is an unusual and interesting website by a dermatologist interested in both the portrayal of skin disorders in the movies and in the real-life skin conditions of actors. It includes a useful (but not comprehensive) listing of realistic depictations of skin disorders in the movies.