Chemical analysis of 2,000-year-old human teeth from northern Vietnam has confirmed that ancient inhabitants deliberately blackened their enamel using iron-based compounds, settling a long-running debate over whether the dark stains were intentional or simply a byproduct of betel nut chewing. The findings, published in Archaeological and Anthropological Sciences, trace the oldest confirmed evidence of the practice to the Iron Age site of Dong Xa, reframing tooth blackening not as a curiosity but as one of the most enduring beauty traditions in Southeast Asia. Versions of the custom persist in parts of Vietnam and Laos today, connecting living communities to a ritual their ancestors performed two millennia ago.
Iron Sulfate, Not Betel Stains, Behind the Black Enamel
For decades, researchers debated whether the dark residue on ancient Vietnamese teeth came from habitual betel chewing or from a separate, intentional cosmetic process. The new study on teeth from the Dong Xa burial site in northern Vietnam answers that question with hard chemistry. Using non-destructive X-ray techniques and an experimental replication of traditional blackening recipes, the research team identified iron and sulfur residues consistent with iron sulfate, a compound that does not appear naturally in betel residue. The chemical fingerprint matched what ethnographic sources describe as a deliberate lacquering process, not the reddish-brown staining that betel nut leaves behind.
Earlier studies had already established that betel chewing was widespread in the region well before the Iron Age. Gas chromatography and mass spectrometry identified Areca catechu traces on teeth from Bronze Age inhabitants of Nui Nap in northern Vietnam, confirming that the nut’s alkaloids left measurable signatures in enamel. Separate biomolecular work using LC-MS/MS detected arecoline biomarkers, an alkaloid specific to Areca catechu, in Iron Age dental enamel. But the Dong Xa results show that betel staining and deliberate blackening are analytically distinct. The iron sulfate coating found at Dong Xa could not have come from chewing alone, which means the people buried there chose to apply a separate substance to darken their teeth on purpose.
Beauty, Status, and a Challenge to Western Ideals
Why would anyone want jet-black teeth? The answer lies in a value system that predates and contradicts the modern Western preference for white enamel. Ancient poems and folk songs from the region suggest that some communities prized dark smiles, associating the look with maturity, attractiveness, and readiness for marriage. The study authors note that the practice was historically dismissed by Eurocentric observers as an “absolute dark abyss in the mouth,” a characterization that says more about colonial-era bias than about the tradition itself. Inverting contemporary dental aesthetics, blackened teeth signaled that a person had left childhood behind and embraced adult social roles.
The analysis of the Dong Xa teeth also opens questions about who had access to the practice. Researchers have noted that the blackening correlates with gender and status, suggesting it was not universal but instead marked certain individuals within their communities. If only particular people received the treatment, tooth blackening may have functioned as a visible social signal, distinguishing adults from children, women from men, or higher-status individuals from others. That reading fits a broader pattern documented across northern Vietnamese bioarchaeological datasets spanning the Bronze and Iron Ages, where dental modifications tracked closely with population health, behavior, and social organization.
More Than Cosmetic: The Case for Dental Protection
Beyond aesthetics and identity, some researchers have explored whether blackening teeth actually protected them. An ethnographic study of tooth-blackening among Kammu groups in Laos and Vietnam investigated the potential antimicrobial effects of the lacquer coating. Practitioners in those communities have long claimed that the process prevents cavities, and the study found enough evidence to take the idea seriously as a folk dental-health strategy. If iron-based coatings formed a physical barrier over enamel, they could plausibly have reduced bacterial contact and slowed decay, though no controlled clinical trial has confirmed the mechanism.
This possibility reframes the tradition as something more than vanity. In communities without access to modern dentistry, a coating that simultaneously signaled beauty and reduced tooth loss would have carried real survival value. A regional bioarchaeological overview of northern Vietnamese populations across multiple periods provides the broader oral-health baselines needed to test that hypothesis, documenting how dental conditions shifted alongside changes in diet, trade, and social complexity. When those skeletal data are read alongside the new chemical evidence from Dong Xa, they suggest that ancient Vietnamese communities may have independently developed a form of preventive dental care wrapped inside a beauty ritual, centuries before anything resembling modern oral hygiene existed.
A Fading Tradition That Refuses to Disappear
Tooth blackening did not vanish with the Iron Age. It persisted across Southeast Asia for centuries, surviving dynastic changes, colonial rule, and waves of cultural pressure. But the practice has been declining sharply in recent generations. In many places, the spread of Western-style dentistry and advertising has recast darkened teeth as a stigma rather than a mark of refinement. Younger people, exposed to global media images that equate health with a bright white smile, often abandon the custom even when their parents or grandparents still see it as beautiful. That shift has accelerated as rural communities are pulled into national and international labor markets, where appearance can be tied directly to employment opportunities.
Public health campaigns have also played an ambivalent role. On one hand, programs promoting fluoride toothpaste and regular dental checkups have improved oral health outcomes and reduced the need for any protective coating. On the other, messaging that frames naturally dark or modified teeth as a problem to be fixed can deepen the sense that traditional practices are backward. Studies of oral-health behavior in Southeast Asia show how quickly attitudes can change when school curricula, clinic posters, and television spots all valorize the same ideal of white, “modern” teeth. For elders who still remember tooth blackening as a rite of passage, this transformation can feel like a loss of cultural continuity as much as a gain in clinical care.
Reclaiming an Ancient Smile
Archaeological chemistry cannot revive a fading custom on its own, but it can change how that custom is understood. By demonstrating that Dong Xa’s Iron Age inhabitants intentionally coated their teeth with iron sulfate, the new study moves tooth blackening out of the realm of exotic anecdote and into the mainstream of Southeast Asian social history. It shows that what might look like a simple cosmetic choice today was, in fact, a complex practice that intertwined beauty, adulthood, status, and possibly health. For descendant communities, seeing this complexity recognized in scientific journals and museum exhibits can offer a counterweight to generations of dismissive or pathologizing descriptions.
The findings also invite a broader reconsideration of what counts as “advanced” dental care. If Iron Age artisans were able to engineer a durable, protective enamel coating using locally available materials, they were solving many of the same problems that modern dentistry addresses with sealants and varnishes. Rather than treating tooth blackening as a quaint relic, researchers are beginning to see it as one point on a long continuum of human experimentation with the body. As more sites like Dong Xa are analyzed with the same level of chemical precision, they may reveal a mosaic of regional recipes and meanings, reminding us that there has never been just one way to have a healthy, beautiful smile.
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*This article was researched with the help of AI, with human editors creating the final content.
