It goes back to Greek mythology. Here's the explanation from LiveScience (one of my favorite sites
):
The image of serpents wrapped around a staff is a familiar one in the medical field, decorating pharmaceutical packaging and
hospitals
alike. Snakes bites are generally bad news, and so the animal might seem ill-fitting as the symbol of the medical profession, but the ancient emblem actually has a quite a story behind it.
There are actually two versions of the symbol. The winged version is known as a caduceus, andthe stick is actually a staff that was carried by the Olympian god Hermes. In Greek mythology, Hermes was a messenger between the gods and humans (which explains the wings) and a guide to the underworld (which explains the staff). Hermes was also the patron of travelers, which makes his connection to medicine appropriate because, in the olden days,
doctors
had to travel great distances by foot in order to visit their patients.
In one version of Hermes' myth, he is given the staff by Apollo, the god of
healing . In another version, he receives the staff from Zeus, the king of the gods, and it is entwined with two white ribbons. The ribbons were later replaced by serpents, as one story tells that Hermes used the stick to separate
two fighting snakes , who then coiled around his staff and remained there in balanced harmony.
Another, earlier depiction of the
medical
symbol is the staff of Asclepius, thought it has no wings and only one snake. The son of Apollo and the human princess Coronis, Asclepius is the Greek demigod of
medicine . According to mythology, he was able to restore the health of the sick and bring the dead back to life.
In one telling, Zeus killed Asclepius with a thunderbolt for disrupting the natural order of the world by reviving the dead, while another version states that Zeus killed him as punishment for accepting
money
in exchange for conducting a resurrection. After he died, Zeus placed Asclepius among the stars as the constellation Ophiuchus, or "the serpent bearer."
The Greeks regarded snakes as sacred and used them in healing rituals to honor Asclepius, as snake venom was
thought to be remedial and their skin-shedding was viewed as a symbol of rebirth and renewal. Which is a good thing to keep in mind the next time you spot a medical alert bracelet featuring the seemingly sinister serpents.
