In some parts of Vietnam, shiny black teeth have been considered a high standard of beauty since at least the late 1800s. But now archaeologists have traced the practice back 2,000 years and discovered that ancient humans used abundant iron resources to dye pearly whites black.
In a study published January 22 in the journal Science of Archeology and Anthropology, researchers examined human remains from Dong Sa, an archaeological site in the Red River Delta in northern Vietnam. The settlement of Don Saa was occupied during the Iron Age (550 BC to 50 AD) and the cemetery contained a large number of human bones with a unique tooth color. To understand how people discolored their teeth thousands of years ago, researchers used a variety of techniques to non-destructively analyze skeletal enamel.
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“We believe that the combined presence of Fe and S signals is a strong indicator of the involvement of iron salts,” study lead author Yue Zhang, an archaeologist at the Australian National University, told Live Science via email. Plant materials are now also used as part of the teeth-blackening process, so the finding of traces of plant materials on ancient teeth likely also points to that practice, Zhang added.
One modern method of blackening teeth is to combine iron-based substances with tannin-rich plant materials such as betel nut (Areca catechu). Chewing betel nut has been popular for thousands of years among peoples of the Pacific and Southeast Asia, and long-term use of the natural irritant can stain a person’s teeth and gums red or reddish-brown. However, when tannic acid and iron salts combine and are exposed to air, it becomes a deep black color.
Based on information about modern humans blackening their teeth, researchers believe that the ancient tooth-blackening process likely involved days or weeks of applying a mixture of iron and tannins to achieve the dark shade. However, once this process was complete, a person’s teeth would remain black for the rest of their lives, requiring touch-ups every few years to keep them shiny.
“This practice is still seen today not only in Vietnam but also in a wider range of Southeast Asia,” Zhang said.
The researchers say that while the exact procedure for blackening teeth likely changed over time, the underlying mechanism responsible for the dark color – the interaction of tannic acid and iron salts – was likely the same. This means that the presence of iron salts and sulfur in ancient teeth could be considered diagnostic markers of intentional blackening, the researchers wrote.
“To our knowledge, our study of Dongsa teeth is the first to link archaeologically discovered blackened teeth to modern intentional tooth blackening,” Zhang said.
However, unanswered questions remain as to why the habit of blackening teeth arose.
One possibility, the researchers noted, is that blackening may have been developed as a less extreme version of dental mutilation, the act of removing healthy teeth as a rite of passage or group identification marker. Another possibility is that blackening was invented to enhance the visual impact of the coloration from chewing betel nut.
Regardless of the original purpose, the researchers write, “teeth blackening probably became widespread around the Iron Age, when iron instruments became more available for producing blackening dye pastes.”
Zhang, Y., Wang, Y., Nguyen, V., Iizuka Y., and Hung, H. (2026). The Kingdom of Teeth Blackening 2,000 Years Ago: Tracing the custom of teeth blackening in ancient Vietnam. Science of Archeology and Anthropology, 18(2). https://doi.org/10.1007/s12520-025-02366-5
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