The chemical in garlic
By: Eric Coleman, 3rd yr Chemist,
Garlic was once thought to possess magical powers against evil and was widely used in charms and spells. Egyptians swore on a clove of garlic when they took a Solemn oath. The builders of the pyramids ate garlic during the construction. Romans took it to strengthen them in battle. It was the herb of Mars, the Roman god of war.
Many legends surrounding garlic have to do with strength, speed and endurance. In the Far East, herbalists used it to treat high blood pressure and respiratory problems. In 1550, an Egyptian medical listing recommended garlic for 22 problems. The Romans said it would cure 60 ailments.
Aside from these, the more traditional folklore is that garlic can ward off vampires and werewolves. See the site about Buffy for more details!