Apart from being the title of an obscure early 1980s B-side by The Cure, heroin face is an obscure medical condition similar to rosacea, which afflicts alcoholics and makes their faces turn red, and their noses turn into giant fruitlike golf balls.
Heavy heroin users develop contorted facial features and facial emaciation, as well as (generally) gum disease and just plain ol' unattractiveness. Two of the most well-known heroin faced men are Iggy Pop, who wilted flowers on the cover of his 1977 album Lust for Life, and Brett Anderson, the lead singer for Suede. Not too many women get heroin faces, though a few I can think of are Marianne Faithful in the early 70s, Nancy Spungeon, and mid-90s Courtney Love. Other possibilities are Chrissie Hynde of The Pretenders, and, if you squint your eyes enough, maybe Debbie Harry of Blondie.
Anderson (like Iggy Pop before him) was quite attractive prior to his discovery of heroin; now in the inevitable Suede music videos, the camera is always jammed practically up his now pointed nose and shows the viewer the premature wrinkles, excess cartilage, and cheekbones that protrude too far from his face. A few years of regular heroin use, and he's starting to resemble Michael Jackson, who has achieved heroin face on his own, without heroin, through plastic surgery.
Heroin face usually afflicts those who were skinny to begin with the most; for example, longtime junkie Steve Earle, who has always been somewhat portly despite his addiction, has kept a modest physical appearance because of his build. Megadeth's Dave Mustaine, in the late 80s and early 90s, had a heroin face but managed to hide it fairly well due to his excessive indulgence in just about every other drug available to him when he wasn't strung out on heroin. Other users of heroin, like the mid-70s David Bowie, and late-80s Nikki Sixx of Motley Crue, completely avoided heroin face somehow. Perhaps it has to do with genetics. Some get the short end of the stick, as always, and former Guns N' Roses drummer Steven Adler (a junkie for 10+ years) turned out to be uglier than Iggy Pop by several orders of magnitude.
Perhaps the greatest example of a man with heroin face is the legendary Keith Richards. Iggy Pop and Steven Adler pale in comparison to the ugliness that the venerable Rolling Stones guitarist has done to himself over the years.
While it's not actually a disease (anymore than drug addiction is a disease), it's difficult to classify. I was unable to find any literature or medical whitepapers on the subject, so I would venture a guess that the hard lines, rapidly-appearing wrinkles, and pointed noses are caused by the repeated grimaces of the users as they inject, or because of the stress their bodies undergo when they are unable to procure any heroin to satiate their addictions.
The aforementioned cover of Lust for Life by Iggy Pop can be found at the following URL:
http://www.terzon.com/musicfs/ip_lfl.jpg (Thanks to panamaus for providing a better-quality cover of the album. I had been using one from amazon.com that was kind of small.)
It's truly a smile that could, uh... sink a thousand ships. At least it's a good album, though.