Garlic

Garlic is Allium sativum, and the chemistry behind its reputation is well characterised and slightly counter-intuitive.

Intact garlic contains almost no allicin. What it contains is alliin, an odourless sulfoxide, held separately from the enzyme alliinase. When the clove is crushed or cut, the cell compartments break, the enzyme meets the substrate, and allicin is generated within seconds. This is a chemical defence system that fires on damage. It also means that how garlic is prepared changes what it delivers: heat denatures alliinase, so garlic cooked whole and garlic crushed and rested before cooking are not pharmacologically equivalent.

Allicin has demonstrable antibacterial and antifungal activity in vitro, which was investigated seriously in the early twentieth century and again during the world wars when antibiotics were scarce or unavailable. It is unstable, breaking down rapidly into a range of sulfur compounds, which limits what it can do inside a body. Evidence for garlic supplements affecting blood pressure or cholesterol is mixed and the effects, where found, are small.

So the folk reputation as a defence against infection is not baseless, and it is also not a modern claim: it is old, widespread and independently arrived at across Europe, the Middle East and Asia. Culpeper calls it the poor man's treacle, treacle here being theriac, the classical compound antidote to poison, and assigns it to Mars on its heat and pungency. Sharpness of taste is the recurring signature of the whole Mars group in his scheme.

Garlic's protective reputation is ancient and geographically enormous. It is attested in Egypt, where it was fed to workers and placed in tombs, in Greece and Rome, across the Islamic world, in India and in China. The consistency is striking and probably has a plain cause: a substance with a violent smell and a real antiseptic action, cheap and available everywhere, is going to be read as driving something off.

The vampire association is far more recent than the rest and should not be back-projected. Southeast European vampire folklore is documented from the eighteenth century onward and does include garlic among a wide range of apotropaics, alongside iron, thorn, running water and various ritual measures. What fixed garlic as the vampire repellent in the general imagination is Bram Stoker's Dracula of 1897, where Van Helsing packs the sickroom with garlic flowers, and then twentieth-century cinema, which needed a visual shorthand. A nineteenth-century novel and a twentieth-century film industry are the proximate source of a belief usually described as ancient peasant lore.

There is also a documented tradition running the other way. Several sources report garlic being avoided by those in states of ritual purity or religious discipline, it appears among substances discouraged in some Hindu and Buddhist monastic contexts as inflaming the passions, and Islamic hadith record a prohibition on entering the mosque after eating it. A plant read as protective in one frame is read as polluting in another, on essentially the same observation about its pungency.