Halloween season wouldn’t be what it is without the undead. This week on Reactions, we unpack the chemistry that may have inspired one of our favorites: the vampire. When you think “vampire” some of today’s most popular vampires might come to mind. Attractive bloodsuckers with pale, sometimes sparkling skin. But in the 18th and 19th centuries, when European vampire lore first really took off, they were a bit more…morose and, instead of that crystal-clear skin, they appeared kind of sickly with a reddish complexion. Vampires were often depicted as men from poor, rural areas, who, after dying–often from diseases like the plague–would emerge from their coffins to wreak havoc on a nearby town, sucking the blood of humans, turning them into vampires as well. So how did this folklore come about? Possibly…disease.