On Halloween, the streets will be filled with children dressed up as witches, vampires and other frightening creatures. For the past fifty years, research has speculated that the myth of one of these monsters can actually be traced back to a medical  disorder.

Vampires are typically characterized by sensitivity to sunlight, pale complexion, and a diet of human blood. Some scientists have speculated that there is a link between these traits and the symptoms of porphyria. It appears that the age-old vampire could have been no more than a victim suffering from this disease.

Porphyria is a collection of related diseases that involve pigments known as porphyrins, which accumulate in the skin, bones and teeth. One of the best-known porphyrins, and the agent of this disease, is heme—the pigment in red blood cells and a component of the oxygen transporter hemoglobin.

Essentially, all versions of porphyria result from faults in the body’s production of this pigment. Heme is made in a sequence of eight steps, each equally important and catalyzed by a separate enzyme, as in a factory assembly line. If any of these steps is disrupted due to a mutation or an environmental toxin, the entire assembly line is halted. As a result, products of earlier steps, including some porphyrin intermediates, can build up to toxic levels.

The problem occurs when these porphyrins accumulate in the skin and other organs. While porphyrins are benign in the dark, they are transformed into corrosive, flesh-eating toxins when exposed to sunlight.

Porphyrins readily absorb both visible and ultraviolet light in order to transfer energy to oxygen molecules. Through this process they form singlet oxygen. Due to its reactivity and interactions with the skin, this derivative of oxygen can cause the symptoms suffered by victims of porphyria.

Along with an acute sensitivity to sunlight, the disruption of heme production means that the body cannot produce enough heme to form normal red blood cells, eventually leading to hemolytic anemia.

The type of porphyria that some researchers believe to have inspired vampire tales is known as congenital erythropoitic porphyria. It’s one of the worst forms of the disease, and causes symptoms such as gum and skin disfigurement.

Dr. Joe Schwarcz, the director of McGill’s Office for Science and Society, examined this connection between vampires and porphyria. In his article, “The Myth of Vampires and Porphyria,” he noted that Dr. David Dolphin, one of Canada’s top chemists, suggested the porphyria victims’ sensitivity to sunlight, and the possibility that receding gum can give the appearance of fangs. He believes this could have led to the creation of the myth of vampires.

However, while there are some links between porphyria victims and the mythological vampire, many aspects of the vampire-porphyria hypothesis do not hold up to scientific scrutiny.

For instance, Dr. Schwarcz mentioned that some researchers have suggested that “[as] porphyria now is treated by injection of blood products such as hematin that will interfere with porphyrin synthesis, at one time victims may have attempted self-treatment by drinking blood.”

Unfortunately, the ingestion of blood on its own, as opposed to the infusion of the pigment and blood product of hematin, would not provide any treatment for the disease.

Nonetheless, while science has yet to come to a consensus as to whether or not the porphyria-vampire hypothesis holds true, it is not uncommon for mythology to be derived from medical causes or natural disasters of the past. People crave explanations for unknown phenomena, and most often these explanations take the form of story and myth. Whether or not porphyria is the link to the creation of vampire stories, it is not unlikely that there were some medical or other natural phenomena that caused the ancient Chaldeans in Mesopotamia—the people to whom the first vampire myth can be traced—to tell tales of such a creature.