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A 2,000-year-old skull shows a layer of black pigment on the teeth of an individual from Dong Xa, Vietnam. | Credit: © 2026 Zhang et al., Archaeological and Anthropological Sciences
Shiny black teeth have been considered a high standard of beauty in parts of Vietnam since at least the late 1800s. But now archaeologists have traced the practice back 2,000 years, discovering that ancient people used its abundant iron resources to paint themselves. pearly white black.
In a study published Jan. 22 in the journal Archaeological and Anthropological Sciencesresearchers investigated skeletons from Dong Xa, an archaeological site in the Red River Delta of northern Vietnam. The settlement at Dong Xa was occupied during the Iron Age (550 BC to AD 50), and the cemetery held numerous skeletons with unique tooth colors. To find out how humans discolored their teeth thousands of years ago, researchers non-destructively analyzed the enamel of the skeleton using a variety of techniques.
When they targeted the colored areas of tooth enamel using X-ray fluorescencethat measure the X-rays emitted by a sample to characterize its chemical composition, found a high concentration of iron oxide, the researchers wrote in the study. Next, they used scanning electron microscopy with energy dispersive spectrometry (SEM-EDS). This technique involves bombarding a sample with electrons, which produces characteristic X-rays chemical elements in evidence. The researchers found that the discolored ancient enamel samples from Dong Xa were positive for iron (Fe) and sulfur (S).
“We believe that the combined presence of Fe and S signals is a strong indicator of the involvement of iron salts,” lead author of the study. Yue Zhangan archaeologist at the Australian National University told Live Science in an email. Nowadays, botanical materials are also used as part of the tooth-blackening process, so finding traces of them on ancient teeth is likely to signify the practice as well, Zhang added.
A modern method of blackening teeth involves combining an iron-based substance with tannin-rich plant material such as betel nuts (Areca catechu). Betel nut chewing has been popular for thousands of years among the peoples of the Pacific and Southeast Asia, and prolonged use of the natural stimulant can stain a person’s teeth and gums red or reddish-brown. But when tannic acids and iron salts are combined and exposed to air, they create a dark black color.
Based on information from modern populations that blacken their teeth, researchers suspect that the ancient blackening process probably involved several days or weeks of applying an iron-tannin mixture to achieve the intensely dark shade. But once the process was complete, the person’s teeth remained black for life, requiring touch-ups every few years to keep their shine.
“The practice is still observed today, not only in Vietnam, but also more widely in parts of Southeast Asia,” Zhang said.
A Vietnamese woman carries her grandson on her back. | Credit: Getty Images
While the precise procedures for darkening teeth have likely changed over time, the underlying mechanism responsible for the dark staining—the interaction between tannic acid and iron salt—was likely the same, according to the researchers. This means that the presence of iron salt and sulfur on ancient teeth can be considered a diagnostic marker of intentional blackening, they wrote.
“To our knowledge, our research on the Dong Xa teeth is the first to connect blackened teeth discovered archaeologically with modern practices of intentional tooth blackening,” Zhang said.
But there are still unresolved questions as to why the practice of blackening teeth arose.
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One possibility is that blackening was developed as a less extreme version of tooth ablation, a practice that involves removing otherwise healthy teeth as a rite of passage or as a marker of group identification, the researchers noted. Another possibility is that blackening was invented to enhance the visual impact of the coloring that resulted from chewing betel nuts.
Regardless of the original purpose, the researchers wrote, “tooth blackening plausibly spread around the Iron Age, when iron tools became more accessible for the production of blackening dye paste.”