Fashion trends are often fleeting. But some styles survive for millennia because stylish folk from ancient times had fashion statements literally engraved into their bones.

According to historical records, polished black teeth were considered a high standard of beauty in parts of Vietnam as early as 400 BCE. Archaeologists have now uncovered physical evidence that this was the case at least 2,000 years ago, reporting their findings in a recent paper published in Archaeological and Anthropological Sciences. For the study, researchers used noninvasive methods to investigate skeletons found in Dong Xa, a region in northern Vietnam.

“This research clarifies both the antiquity and the distinctive techniques of tooth blackening in Vietnam,” the team explained in its paper, adding that the practice “underscores a culturally embedded expression of identity within wider networks of interregional interaction and exchange.”

A history of black teeth

Pitch-black teeth might sound off-putting, given the modern preference for bright white teeth. Indeed, Western influences in Asia have phased out the tradition for younger generations, but tooth blackening has a rich history of cultural significance across South Asia, Oceania, and certain parts of Africa and America, according to the paper.

“The practice is still observed today, not only in Vietnam, but also more widely across parts of Southeast Asia,” Yue Zhang, the study’s lead author and an archaeologist at the Australian National University, told Live Science.

The Vietnamese in particular were known for their intricate method of tooth blackening, a multi-step process involving “sanitization, red dyeing, black dyeing, and polishing,” the paper noted. However, archaeologists studying skeletons from the region didn’t quite have a consensus on what constituted tooth blackening.

For instance, some skulls had reddish-brown teeth that may have been the product of natural staining from eating certain plants, not necessarily tooth blackening. Accordingly, researchers were divided on the exact procedures for tooth blackening in ancient Southeast Asian communities.

The original beauty standard

The new study sought to make a clear distinction between intentional blackening and natural staining. The team selected skeletons unearthed from previous excavations in the Dong Xa site, located in a region of northern Vietnam known to host a rich archaeological record of bronze artifacts from the Iron Age.

The team used X-ray fluorescence to indirectly identify the chemical composition of the skeletons’ enamel. Based on that analysis, they looked at ethnographic evidence to explore possible links between modern tooth-blackening practices and the ancient skeletons.

Perhaps unsurprisingly, the researchers found high levels of iron and sulfur in the ancient enamel samples. This points to the involvement of iron salts, Zhang told Live Science.

If true, this is consistent with the modern method of tooth blackening, a weeks-long process that uses a combination of iron salts and tannin-rich plants, such as betel nuts, to dye teeth a deep black. It would also mean the process left people with jet-black teeth for their entire lives.

Something to chew on

The implications of the new findings extend beyond ancient beauty standards, according to the paper. Historical records have noted “significant technological and social transformations during the Iron Age” in modern-day Vietnam. This led to the proliferation of iron use in this particular community, so it makes sense that prevalent beauty standards had something to do with iron use, the researchers explained.

On the other hand, biomolecular evidence for betel nut chewing—presumably a separate practice from tooth blackening—dates as early as 2,000 BCE and was observed beyond Vietnam. The potential connections between the two, therefore, could be another opportunity for investigations, the researchers noted.

But the findings highlight the sheer longevity of tooth blackening in Vietnam, regardless of its diminished influence in the region. It truly seems to be a fashion trend that lasted more than a few lifetimes—remarkably, as the new study shows, with few changes to the methods.