There are many variations of the folkloric tale of the 4 Thieves oil, which is an ancient essential oil blend.
The oils used, has traditionally been valued as antiviral and antibacterial remedies. One version of the tale is, that 4 men, who were originally working as perfume and spice merchants, became thieves during the time of The Black Death in France.
They robbed sick peoples homes without getting sick. When captured and ready to receive their (death) sentence, they were asked by the judge to reveal their secret remedy, and, according to the tale, they made a special blend of essential oils and applied it to their temples, hands and feet, and that they wore masks. From then on, doctors who treated the Black Death Patients started wearing beaky masks with that essential oil blend while treating patients.