There's lots of dirty sex in this play. We're talking prostitution, infidelity, and STDs. Well, we're not really talking about it, and that's the problem. The characters in Ghosts treat sex like you treat sex between your parents: they pretend it doesn't exist. But, the great irony is that it does exist. Big time. With no room for sex in this upstanding, moralistic society, the overwhelming natural force has to go somewhere. The only place left for it is somewhere dirty. Like Engstrand's Sailor's Home (a brothel).
In the life-denying ethic of this Norwegian society, sex is pushed to the side and twisted into something diseased or dishonorable.
With his drink and women, Captain Alving represents the Dionysian element that continues to rears it head in Mrs. Alving's world, despite her attempts at banishment.