Here’s a look at the medical conditions and deformative diseases that are really behind the folklore and legends of those things that go bump in the night.

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Vampires- Porphyria Cutanea Tarda (PCT)

Characteristic features: Skin pallor, protruding fang-like teeth, avoidance of daytime light, drinks blood, orders pasta without garlic.

The title character of Bram Stoker’s Dracula established the modern conceptualisation of the vampire. But, perhaps Stoker’s novel, countless films, and traditional folklore have all misunderstood the wretched vampire. Many scholars have suggested that the vampire legend may have its roots in the dermatologic condition known as porphyria. In porphyria cutanea tarda (PCT), the most common subtype of porphyria, the exposed skin of patients blisters in sunlight. This photosensitivity may lead to avoidance of daylight and subsequent skin pallor—a hallmark characteristic of the dark-dwelling vampire.

“Moreover, the skin around the patient’s mouth might retract, as if tightening from sun damage. This skin retraction may consequently reveal the teeth and cause them to appear more prominent,” wrote authors in JAMA Dermatology. “It is ironic, however, that vampires were thought to prey on humans and survive by drinking their blood, because repeated phlebotomy is a modern antidote for PCT.”

In addition, the urine of PCT patients appears red to brown. Old-world folk may have suspected that the reason why a vampire-like person’s urine is the color of blood was because that person was indeed drinking blood.

And the garlic? Garlic contains a chemical that is believed to exacerbate porphyria symptoms; people suffering from PCT would naturally avoid it.

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Werewolves- Lycanthropy & Hypertrichosis

Characteristic features: Full-body hair growth, elongated cuspids, claw-like fingernails, symptoms triggered by full moon, highly susceptible to silver bullets.

Werewolves have been around a long time. The ancient Roman poet Ovid told the tale of King Lycaon, who tried to trick the Greek god Zeus into eating slaughtered human meat. As payback, Zeus turned Lycaon into a savage wolf to match his inner brutishness.

Two notable medical conditions are associated with the history and folklore of werewolves.

The first is clinical lycanthropy, which is still diagnosed today—although very rarely. Clinical lycanthropy is a psychotic illness in which a patient has delusions or hallucinations of becoming a wolf or other animal, accompanied by animal-like behaviors, such as howling, snarling, and walking on all fours. Diagnosis is typically attributed to psychiatric disorders, such as bipolar disorder, psychotic depression, schizophrenia, or personality disorder.

Even in ancient times, many medical practitioners believed lycanthropy to be a delusional disorder. The Greek physician Marcellus of Side described lycanthropy sufferers as melancholics who “roam out at night and mimic the ways of the wolves or dogs and mostly loiter by the grave monuments until daybreak.”

In none of these cases does the patient physically transform into a wolf, which brings us to the second medical condition associated with werewolves: hypertrichosis, or an abnormal amount of hair growth over the entire body or in localized areas. (Hypertrichosis is not to be confused with hirsutism, which is male-pattern hair growth in women or children.)

Hypertrichosis, also called werewolf syndrome, can be congenital or acquired. The triggers that initiate the mechanisms of this excess hair growth are largely unknown.

In a subtype of hypertrichosis, congenital hypertrichosis terminalis (also called congenital hypertrichosis universalis), patients develop thick pigmented terminal hair all over the face and body, giving them a werewolf-like appearance. Individuals have been described as “dog-men,” “hair-men,” “ape-men,” and, of course, “werewolves.” Cases are extremely rare, occurring in only 1 in 1 billion to 1 in 10 billion. Fewer than 50 cases have been documented.

So, where did the moon-activated shapeshifting and the mortal silver bullets come from? They were largely invented by Hollywood in early werewolf movies.

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Witches- Ergotism

Characteristic features: filiform warts, cackling laughter, often accompanied by nigrum cattus, wood splinters in “sensitive areas” resulting from broomstick riding.

The town of Salem, MA, is synonymous with witchcraft. In 1692, several young girls in Salem developed an unexplained illness that manifested with convulsions, hallucinations, screaming outbursts, temporary blindness, and skin lesions. The local doctor’s diagnosis? Bewitchment. The girls accused three women in the town of bewitching them. Hysteria spread. By the time things settled down, 20 people had been executed for witchcraft.

One proposed explanation for the girls’ unexplained illness: ergot poisoning due to a fungus (Claviceps purpurea) found in rye and other grains.

“Outbreaks of ergotism are more likely to occur in the spring after a cold and wet winter in rural regions where rye is a common source of nutrients,” wrote researchers in JAMA Dermatology. “The weather conditions preceding the epidemic in Salem, where cultivation of rye was commonplace, were ideal for just such an outbreak.”

Several of the accused reportedly had discoloration and edema of the skin, described as a “witch’s mark.” This could be explained by vasoconstrictive effects of the ergotamine toxin, the researchers pointed out, because it results in desquamation and necrosis of tissue, edema, and loss of peripheral sensation.

“Victims of ergotism describe feeling delirious, lethargic, and manic, and even report hallucinations or changes in vision,” the JAMA authors wrote. Court records of the Salem witch trials reveal ergotism-like symptoms, including “temporary blindness, deafness, burning sensations, and visions like a ‘ball of fire’ or ‘multitudes in white glittering robes’.” (Indeed, the hallucinogen LSD is a derivative of ergot.)

But what about riding a broomstick? It has to do with “anointing” of the genitals, more hallucinogens, and other things one wouldn’t associate with the magical broomstick-riding world of Harry Potter. 

This  story is part of our Global Content Initiative, where we feature selected stories from our Global network that we feel would be most useful and informative to our Doctor members.

This article was originall published on November 9, 2017.