The math that explains why Y2K is back in fashion

The curious math that explains why fashion trends always come back

By KR Callaway edited by Claire Cameron

If you’ve noticed a resurgence in low-cut jeans, baby tees and velor suits among the cool kids, know that what you’re witnessing isn’t just the return of a trend—it’s math.

Fashion followers know that trends tend to re-emerge in a 20-year cycle, and a new analysis of more than 150 years’ worth of women’s clothing shows that this cycle isn’t just anecdotal: trends in hemlines, necklines and waists on dresses become really cool again about 20 years after their last turn in the spotlight.

“I’ve always been surrounded by this idea that fashion comes back and fashion is cyclical, so I started thinking: Is that actually true?” says Emma Zajdela, a postdoctoral fellow at Princeton University who conducted the new analysis. “I realized that what we had found in the data actually matched perfectly with what was being said in the industry, so that was pretty amazing to us.”

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The analysis was based on data from the Commercial Pattern Archive, a digital database that stores tens of thousands of images of dress patterns dating back to the 1840s, as well as runway images. Using these resources, the researchers were able to build an extensive fashion database, with more than 35,000 images of women’s clothing.

Zajdela and her team analyzed key features of women’s dresses throughout time. By looking along the vertical axis from head to toe, the researchers mapped how seams rose and fell in periodic curves over time and fitted their findings into a mathematical model.

“The mathematical model we use is quite simple, conceptually,” says Zajdela. “It’s based on this idea from psychology called optimal distinctiveness.”

Optimal distinctiveness basically says that people want to belong to a group and still be unique in some way at the same time. When applied to fashion, it means that for a new trend or innovation to succeed, it must be different enough – but not too different – from existing things. People tend to want clothes that feel new and unique, but they also don’t want to deviate too far from what they’ve worn in the past or what others are wearing.

Looking for styles that are both familiar and different can lead some people to gravitate towards more nostalgic designs – especially for younger generations looking for fashion inspiration, as these styles originate from a period they didn’t directly experience themselves and therefore feel more ‘new’.

“Every 20 years you have a new generation of consumers who yearn for the past,” says Shawn Grain Carter, an associate professor of fashion business management at the Fashion Institute of Technology who was not involved in the study. “We love going back to the past to figure out how to … introduce something new to the next generation of consumers.”

It is possible that the 20-year cycle may change in the future: it takes less time to produce new clothes, and social media has given people access to more ideas, which has accelerated trends. But for now, the mathematical model holds up – there’s just a lot more diversity in the latest data, Zajdela explains.

Having established that fashion trends can be described mathematically, the researchers are interested in what similar models can tell us about other areas of human innovation.

“We have this example in fashion, but it shows how human creative endeavours, or innovations, in general can happen,” says Zajdela. “Many other types of innovation have this quality that they need to be different from the past, but not too different.”

The results were presented Tuesday at the American Physical Society’s Global Physics Summit.

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