With Halloween right around the corner, I wanted to learn a little more about garlic and why it is seen as vampire repellant in folklore. According to Vampires.com, many ancient societies considered it to have either healing or protective powers. Garlic contains the antibacterial, allicin, which has some potential health benefits such as decreased blood pressure. Apparently vampires have a bacteria in their blood that is killed by allicin, which offers one explanation as to why vampires must avoid garlic (http://www.gods-and-monsters.com/vampires-and-garlic.html). Unfortunately, Sandvik and Baerheim (1994) discovered that garlic may actually attract vampires after testing leeches. Since their leeches were significantly more attracted to hands with garlic on them, this study recommends that garlic not be used in trying to ward of vampires. Whether or not garlic actually repels vampires is unknown, but we do know that eating garlic can help fight diseases and contribute to overall health.
Sandvik, H. and A. Baerheim. 1994. Does garlic protect against vampires? An experimental study. Tidsskr Nor Laegeforen 114: 3583-3586.