Blistering Therapy

Blistering therapy, also called vesication, was the historical practice of applying an irritant substance to the skin, most often cantharidin drawn from the blister beetle or a mustard plaster, to deliberately raise a blister. The practice rested on the same humoral logic as purgative therapy and bloodletting: physicians believed that drawing fluid to the skin's surface would pull morbid matter out from beneath it and relieve the underlying disease. It was used across Western medicine from antiquity through the nineteenth century for conditions as varied as pneumonia, arthritis and nervous disorders, and it receded through the later nineteenth and early twentieth centuries as germ theory and controlled clinical evidence displaced the humoral framework that had justified it.