According to Frances White of History Answers, the reason behind the plague doctor mask’s peculiar appearance was as sound by the medical science of the era as it is misguided by today’s standards. Back in the day, science believed that plagues such as the Black Death were spread by a vapor known as miasma, which was basically air that had gone very, very wrong. The mask was an attempt to combat the disease by stuffing the beak with nice smells, like spices, herbs and dry flowers. In reality, of course, the concept of miasma was completely imaginary, so the mask was basically just an elaborate air freshener. 

Oddly enough, while the plague doctor has become something of a symbol of the Black Death, it’s very unlikely that the outfit was ever worn during this 14th century plague. In fact, historians tend to attribute the costume to Charles de Lorme, a French doctor who invented it in 1619 as a sort of “doctor version” of a head-to-toe armor. Doctors used it during the Plague of 1656, which tore through Italy and killed an estimated 300,000 people in Naples and 145,000 in Rome.