Last Updated on May 17, 2026 by Staff
A new archaeological study has uncovered evidence suggesting that mercury may have been used as a medical treatment for leprosy during the late medieval period. The research, published in the Journal of Archaeological Science, was led by Dr. Elena Fiorin and her colleagues.
For centuries, mercury was considered an important medicinal substance despite its highly toxic nature. Medieval doctors often used it to treat diseases such as syphilis, skin infections and leprosy. However, proving that ancient patients actually received mercury-based treatments has remained difficult for researchers.
Traditionally, scientists examined bones, hair or teeth to trace mercury exposure in ancient human remains. This new study is the first to investigate mercury concentrations in dental calculus, also known as hardened plaque, to identify possible medical treatments in medieval populations.
The findings provide fresh insight into how people suffering from leprosy may have been treated hundreds of years ago.
Toxic Element
Mercury, also called quicksilver, is a toxic metal known for remaining liquid at room temperature. People can absorb it through inhalation, food, water or skin contact.
During medieval times, mercury was believed to help cure various skin diseases and infections. Doctors often mixed it into ointments containing fats or oils and rubbed the mixture onto the skin.
Because leprosy caused severe skin damage and deformities, mercury became one of the substances commonly associated with treatment. However, historical medical records from many medieval hospitals and leprosaria are incomplete or missing entirely.
This is where dental calculus became important for the research team. According to Dr. Fiorin, hardened plaque forms during a person’s lifetime and can trap tiny particles from food, air and substances entering the mouth.
Unlike bones, which may reflect long-term chemical exposure, dental calculus can preserve evidence of more direct and repeated contact with medicines. Researchers believed it could therefore reveal whether mercury-based treatments had been administered to patients.
Cemetery Study
To test their idea, scientists examined skeletons from two medieval leprosaria: St Leonard’s in Peterborough, England, and St Thomas d’Aizier in France. The remains were then compared with skeletons from two ordinary cemeteries without links to leprosy.
Researchers collected dental calculus samples from 76 individuals and compared them with 45 soil samples taken from the graves. The goal was to determine whether mercury entered the remains during life or after burial through environmental contamination.
The results were striking. Individuals buried in leprosaria showed significantly higher mercury levels than people buried in regular cemeteries.
Scientists also found little evidence that surrounding soil caused the mercury buildup. In many cases, the mercury concentrations inside the dental calculus were far higher than those in the nearby soil.
One especially important case involved two individuals buried side by side. A woman showed mercury levels of 3.8 mg/kg in her dental calculus, while a man buried next to her had only 0.4 mg/kg. Both displayed signs of mercury exposure, but the much higher concentration in the woman strongly suggested medicinal treatment rather than environmental contamination.
Signs of Status
Researchers believe social differences may also have influenced access to treatment. The individuals with the highest mercury levels were buried inside the chapel areas of the leprosaria, locations often associated with higher social standing or privileged care.
This suggests that wealthier or more respected patients may have received more extensive medical treatment than others.
The study also showed that mercury found in surrounding soil at the leprosaria likely came from the decomposition of mercury-treated bodies over time rather than from natural environmental sources such as mining activity.
These findings help researchers better understand how medieval hospitals may have operated and how treatments varied among patients.
Although mercury was dangerous, it was considered valuable medicine during the medieval era because physicians lacked modern knowledge about toxicity and disease transmission.
Future Discoveries
The study highlights the growing importance of dental calculus in archaeology and medical history research.
Scientists say hardened plaque can preserve detailed chemical evidence that helps reconstruct ancient diets, occupations and treatments. It may now become an important tool for studying historical diseases and healthcare practices.
Future research will focus on identifying when mercury treatments first became common and whether all leprosy patients received similar care.
Researchers also plan to compare skeletons with and without signs of leprosy to better understand how medieval doctors approached the disease.
The discovery demonstrates how even tiny traces preserved on teeth can reveal major details about medicine, illness and social life hundreds of years ago.
By combining archaeology with modern chemical analysis, scientists are uncovering new evidence about how people struggled to fight disease long before the arrival of modern medicine.
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