In the Middle Ages, the toxic heavy metal mercury was considered an effective remedy against skin rashes and leprosy. Now tartar samples from dead people from two medieval leprosy infirmaries prove that the heavy metal was actually used to treat leprosy back then. However, the analyzes also show that the dose and extent of mercury therapy depended heavily on individual and social factors.
Mercury is now considered an environmental pollutant and toxic to humans. But in earlier times, mercury was used both as a dye in the form of vermilion and for medicinal purposes. The heavy metal was known for its regenerating and laxative properties and was considered extremely effective against skin diseases and other skin impurities. “In the late Middle Ages and beyond, medicines containing mercury were also used to treat infections such as venereal syphilis and leprosy,” explain Elena Fiorin from Sapienza University in Rome and her colleagues.
Records from the Italian surgeon Theoderic Borgognoni from the 13th century testify to the use of mercury against leprosy. “He describes a ‘Saracen’ ointment that was common at the time for treating leprosy, which consisted of mercury, fats and oils and was applied to the skin,” report Fiorin and her team. In the medical textbook “Liber de diversis medicinis” from the same period, two mercury-containing recipes for the cosmetic treatment of leprosy are also documented. Even later, in the 18th century, there were still doctors who tried to cure leprosy with a 30-day course of mercury, as the researchers explain.
Tartar as a contemporary witness
Fiorin and her colleagues have now searched for archaeological evidence for these historical records. To do this, they analyzed tartar samples from a total of 61 people who were treated as lepers in two leprosariums in the Middle Ages and died there. They were buried in the leprosy cemeteries of St. Leonard in Peterborough, England, and St. Thomas in Normandy. For comparison purposes, the researchers also examined tartar samples from medieval dead from two normal cemeteries as well as soil samples from the respective graves.
Tartar has long been known to be suitable as an archaeological witness, similar to bones and teeth. “It can preserve organic and inorganic remains and therefore reveals a lot about nutrition, activities and medical treatments,” explain Fiorin and her team. However, tartar has never been used to detect medical mercury treatments in earlier populations.
Increased mercury levels in leprosy victims
The analyzes of the medieval dental calculus revealed clear differences between the dead from the leper colonies and the comparison samples. “We found significantly higher mercury levels in the tartar from the leprosarium. On average, it contained 1.2 milligrams per kilogram,” report Fiorin and her team. In contrast, the tartar of the dead from normal cemeteries only contained around 0.37 milligrams of mercury per kilogram. It was also striking that the tartar of the lepers also contained significantly more mercury than the soil in the graves.
According to the researchers, these results indicate that the leprosy patients were actually treated with medicines containing mercury at the time. “There is no historical or archaeological evidence of mines in the areas studied and, to our knowledge, the inhabitants of the leprosariums did not work in mining or metallurgy,” write Fiorin and her colleagues. “Therefore, medicines containing mercury are the most obvious explanation for the presence of this heavy metal in the tartar of these lepers.”
Treatment also depended on social status
Whether someone received such therapy back then also depended on their social status and other factors within the leprosariums. This is also supported by two dead people, an adult man and a child around ten to fourteen years old, who were buried in the chapel of St. Thomas – this in itself was unusual. “Burial in the chapel indicates a higher or privileged social status,” explains the team. Both individuals also had the highest mercury levels of the dead examined in this leprosy cemetery. “One could therefore assume that these people had a greater chance of receiving an expensive medicine such as mercury than others,” state Fiorin and her colleagues.
Source: Journal of Archaeological Science, doi: 10.1016/j.jas.2025.106444