Traces of mercury treatment have been found in the teeth of medieval people

The study was published in the Journal of Archaeological Science. The authors analysed the dental stone of 76 people from medieval burials and compared the data with 45 soil samples from the same graves. This approach helped to test whether mercury got into the tartar during life or after burial.

Important: The work does not prove that all people with leprosy were treated with mercury. But the results do show that some of those buried with leprosy had lifetime exposure to mercury, and the most likely explanation is mercury-based medicines.

Details

Lepra, or Hansen's disease, was one of the most stigmatised diseases in the Middle Ages. People with signs of the disease could be placed in leprosariums, special institutions that were both places of isolation, care and religious guardianship.

The authors of the new paper studied burials from two leprosariums: St Leonard's in Peterborough, England, and Saint-Thomas d'Aizier in France. For comparison, they also took samples from ordinary medieval cemeteries where the burials showed no bony signs of lepra.

The main material was tartar, a hardened plaque that forms on teeth during life. It can retain microscopic traces of food, particles from the environment, substances a person has inhaled or come into regular contact with. In this study, it was used to test for traces of mercury.

Mercury was used in the Middle Ages in medicinal preparations, especially for skin diseases. Such preparations may have been included in ointments based on fats and oils that were applied to the skin. Today it is known that mercury is toxic, but in medieval medicine it may have been perceived as an effective remedy for ulcers, rashes and skin diseases.

The results showed: people buried in leprosariums had significantly higher mercury concentrations in dental calculus than people from control cemeteries. The article states that values in dental stone ranged from 0.11 to 9.7 mg/kg.

To rule out simple post-burial contamination, the researchers tested the soil from the graves. This is an important part of the work: if mercury had entered the remains from the environment, the treatment conclusion would have been weaker. But the analysis showed that the elevated mercury in the dental calculus was most likely related specifically to lifetime exposure.

A curious detail: the highest mercury levels were found in people buried in the more prestigious areas of the leprosarium, including the chapel. The authors speculate that access to treatment may have depended on status, severity of condition, or conditions in the institution. This is not a definitive conclusion, but an important clue that care in leprosariums may not have been uniform.

Why it matters

This work shows the Middle Ages not only as an era of isolation for people with leprosy, but also as a time when they were attempted to be cared for and treated using the treatments available at the time. Mercury was a dangerous substance, yet to doctors of the time it may have seemed like a cure.

The study is also important for archaeology. Usually traces of mercury are looked for in bones, teeth or hair. Here, for the first time, scientists have used dental calculus as a source of data on possible mercury treatment in ancient populations. This expands the tools with which to study the medicine of the past.

The main conclusion is a cautious one: tartar can preserve chemical traces of treatment, even if no written medical records remain. For the history of disease, this is especially valuable because everyday patient care is often less well documented than laws, religious rules, or descriptions of symptoms.

Background

Leprosories in medieval Europe were not just "places of exile." Their role was more complex: people lived there, receiving food, religious support, and probably medical care. But understanding exactly how they were treated is difficult: documents have not always survived, and archaeological traces of treatment are usually indirect.

In recent years, dental calculus has been increasingly used as a biological archive. Food particles, traces of plants, microbes, medicinal substances and other microscopic evidence of human life are found in it. In this case, it has helped to see not diet but possible medical practice.

The new work is particularly interesting because it compares tartar with soil from the same burials. This makes the conclusions more convincing: the researchers didn't just find mercury, they tried to understand when and where it got into the remains.

Source

Elena Fiorin et al, "Mercury treatment in late medieval European leprosaria? New data from human dental calculus", Journal of Archaeological Science, 2026. The study analysed dental calculus from 76 individuals from medieval burials, including the leprosaria of St Leonard's in England and Saint-Thomas d'Aizier in France, as well as 45 soil samples from the graves. The authors measured mercury concentrations and concluded that the elevated levels in people from the leprosariums probably reflect lifetime exposure to mercury, possibly related to medical treatment of leprosy.