WASHINGTON • Among the few tell-tale signs of a movie villain are a sadistic laugh, a penchant towards explaining evil plans - and a skin disease.
Dermatologists are taking notice with a critical eye.
As outlined in a recently published study in Jama Dermatology, movie villains are often afflicted with skin conditions such as alopecia (hair loss), facial scars and periorbital hyperpigmentation (a condition leading to dark circles around the eyes).
Some advocacy groups have long attacked Hollywood for these portrayals. When The Da Vinci Code was released in 2006, for example, its villain was a monk-assassin with albinism named Silas.
Mr Michael McGown, executive director of the National Organisation for Albinism and Hypopigmentation, noted that it was the 68th movie since 1960 to feature an albino villain.
In the study, researchers looked at the top 10 villains from the American Film Institute's "100 greatest heroes and villains" list.
Six of the 10 villains featured visible dermatologic conditions.
Among those characters were Dr Hannibal Lecter, the cannibalistic serial killer from The Silence Of The Lambs (1991) and Regan MacNeil, a young girl possessed by the devil in The Exorcist (1973).
The most obvious is Star Wars' Darth Vader, a man so hideously deformed, he wore a mask to hide his visage.
A glance down the rest of the list found many more villains with dermatological conditions, such as Freddy Krueger's severe scarring in A Nightmare On Elm Street (1984) and Cruella de Vil's poliosis and deep rhytides in 101 Dalmatians (1996).
Using dermatological conditions to symbolise evil was even starker when the top 10 villains were contrasted with the top 10 heroes.
Of these heroes, only four showed any sort of cosmetic facial damage - Indiana Jones, Rocky Balboa, Rick Blaine (Casablanca, 1942) and Will Kane (High Noon, 1952).
The former two had small facial scars, while the latter sported lacerations inflicted while they were defending some form of "good".
The heroes' scars were different from those of the villains'.
They are much subtler and shorter in length. They are neither created with prosthetic make-up nor commented on during the narrative, unlike the scars of the villains.
In addition, each villain has multiple facial scars whereas each hero has a single facial scar.
While the study might seem anecdotal, its authors warned that "the implications... extend beyond the theatre".
"Specifically, unfairly targeting dermatologic minorities may contribute to a tendency towards prejudice in our culture and facilitate misunderstanding of particular disease entities among the general public," the study said.
Mr Vail Reese, a dermatologist, keeps an entire blog - fittingly named Skinema - dedicated to exploring skin conditions in film.
"The majority of films use skin disease to convey a character's devious motivations. Finally, very few films depict characters with skin disease sympathetically," he wrote.
"We must remember that the attitude towards skin disease in movies, to some extent, both reflects and informs the perceptions of our society. Even today, individuals with non-infectious diseases such as psoriasis and vitiligo are treated as if they have the plague."
Added Mr Reese: "Skin disease does not represent inherent evil, but rather a difficult and, at times, disabling condition."
But some recent shows portray skin disease as a disabling condition, rather than shorthand for evil.
HBO's acclaimed drama The Night Of features a kind-hearted character who suffers from psoriasis. Online magazine Slate called the show "a star vehicle for eczema". One dermatologist told Slate the show "really resonated" with one of her patients.
It is too early to know if The Night Of signals a new trend, but dermatologists will be keeping a very close watch.