Garlic is a pungent plant in the allium family, known around the world for its health benefits. There is, however, one supernatural creature that is harmed, not helped, by garlic: vampires. It’s commonly said that garlic repels them, hinders their ability to feed on human blood, and can even kill them.

There are several theories about why the particular plant is said to repel the blood-sucking nightwalkers continue to circulate. The most common theory connects vampirism to a blood disorder called porphyria. A person with porphyria lacks the enzymes that turn a chemical called porphyrin into heme—part of a protein in red blood cells called hemoglobin—which causes the porphyrins to build up. This leads to physical effects including receding gums (making teeth look longer), pale skin, sensitivity to sunlight, and an intolerance to foods with a high sulfur content—including garlic. Theoretically, people with porphyria could replenish their heme supply by drinking blood, so it’s no wonder the connection was made between the disorder and vampirism.

Another theory revolves around the argument that it’s not porphyria, but rabies, that connects vampirism with an aversion to garlic. People become infected with the virus after being scratched or bitten by a rabid animal. Rabies symptoms include aggressiveness and the urge to bite; insomnia that could potentially cause night wandering; a fear of water; and hypersensitivity that leads to an adverse reaction to mirrors, light, and strong odors—including odorous plants like garlic. Some scientists have even linked the vampire legend to a 1720s rabies epidemic in Hungary.

Because vampires were thought to be created by a disease, it was believed a food known for its healing powers could potentially “cure” the infection that led to their existence. People did more than just carry garlic around as protection: To keep vampires from entering their homes, they’d also hang the plant in their windows and rub it on their keyholes and chimneys.

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This article was originally published on www.mentalfloss.com as Why Can’t Vampires Eat Garlic?.