The Rod of Asclepius is the older and more accurate symbol of medicine. It shows one snake wrapped around a plain staff, with no wings. Asclepius was the Greek god associated with healing, medicine, and physicians. Because of that connection, his serpent-entwined staff became a lasting symbol of medical care and the healing arts.
The caduceus, by contrast, shows two snakes wrapped around a winged staff. This was the staff of Hermes, known to the Romans as Mercury. Hermes was the messenger of the gods, but he was also associated with travelers, merchants, trade, language, diplomacy, thievery, and cunning. In other words, the caduceus originally had more to do with communication, commerce, negotiation, and trickery than with healing.
The confusion became especially common in the United States. In 1902, the U.S. Army Medical Corps adopted the caduceus as an insignia, even though the Rod of Asclepius was the more traditional medical symbol. Over time, the caduceus became widely recognized in America as a medical emblem, despite its earlier association with Hermes rather than Asclepius.
The easiest way to remember the difference is simple: one snake means medicine; two snakes and wings mean Hermes. The Rod of Asclepius symbolizes healing and physicians. The caduceus points to messengers, merchants, travel, negotiation, and clever speech.
So the next time you see a medical logo with two snakes and wings, you are not looking at the ancient symbol of medicine. You are looking at a symbol that history borrowed, confused, and never quite gave back.