In 1985 biochemist David Dolphin proposed that the vampires of folklore may actually have been people suffering from porphyria, a group of rare, largely hereditary blood diseases.
Porphyria is an hereditary disease caused by an anomaly of the metabolism [overproduction and accumulation of the porphyrins or the “purple pigment”].
It is practically a form of septicemia – the toxins build up in the blood and they gradually poison the muscles. As the illness progresses the color of the urine will change, taking shades of red, purple or even brown.
It will pass down from one generation to another in some cases remaining latent. The disease can this way skip a generation or two and resurface in unexpected branches of the genealogical tree.
Presently the illness is completely treatable and the number of cases seems to be dropping, but in the Middle Ages things weren`t as simple!

In those days a porphiric could be easily mistaken for a vampire because of the sensitivity to sunlight. Even mild exposure can cause severe disfigurement. Facial skin may scar, the nose and fingers may fall off, and the lips and gums may become so taut that the teeth project like fangs. It`s only natural that in the terminal stages the ill would leave their houses only at night – just like vampires.
We even find references of blood rituals.
One might argue that, since it is a blood disorder one might need to take the blood of another to replace his own ill blood. I cannot speak for what was believed back then although I do think it is possible that people were convinced that the “vampires” drank blood to sustain their live form.
Porphyria victims don’t crave blood. Drinking blood will not alleviate their symptoms, nor has there ever been a general belief that it would. The blood chemicals porphyria victims need do not survive digestion.
We even have ties between this disease and garlic.
Most of the ill are allergic cu garlic therefore cannot stand it. If you remember my ~Superstitions~ article, I mentioned the fact that priests would distribute garlic during mass to test for living vampires!
Modern medicine explains that the substances that normally make garlic such a great remedy for a healthy organic system, when combined with that of a porphiric can have poisoning effects. Ingestion of garlic first affects the stomach and they often cough it up.

Another interesting fact is that, since porphyria is hereditary, it falls into the idea that vampires returned to feed on their family.
And here I feed the need to add a couple of observations: modern ~Literature~ and ~Movies~ show that the transformation is almost instantaneous [like in “Interview with the vampire”] or that it might take up to a night [like in “True Blood” or “Vampire Diaries”], but the old legends state that sometimes the transformation can take longer. Even years!
So there was enough time for a child to grow and his porphiric gene be activated, or for another child – with an already active gene to be born.
You can therefore imagine the psychological effect a single case of porphyria could have had on a rural community in a village in the Middle Ages. Especially considering that in such a community everybody is related to… everybody.
To that, add the tension created by priests that castes fear into the peasants.

So lets recap:
– paleness
– sensitivity to sunlight
– [sometimes] allergic reactions to garlic
– skin burns if exposed to the sun
– speculations that blood drinking is required to recuperate a healthy state
– [hereditary disease] chain periodic deaths within a family