Nadia Boujarwah knows personally that shopping for plus-size clothes can be difficult. But it was only while she was a student at Harvard Business School that she realized something else: The lack of options presented a commercial opportunity.

A year after graduating, Boujarwah and a business school classmate, Lydia Gilbert, began testing the market by acting as personal shoppers. And they saw their opening: offering women sizes 14 and up five articles of clothing chosen by a stylist who takes into account individual preferences. In 2015, they started an online retail site, Dia & Co.

“I hadn’t intended for retailing to be a career choice,” Boujarwah said. “But when I was in business school, I realized that my formative experiences were shared with millions of women. It was a call to arms for me. This was a problem for many women that I could play a role in.”

The scarcity of larger sizes stems from a deeply rooted stigma in the fashion industry — many designers either ignore or reject requests to offer their styles above a certain size.

There are also manufacturing complications: Progressing from size 2 to 12 can be a simple matter of scale, but larger sizes often require a separate pattern to account for different proportions and entail more fabric, raising the production cost.

“I sat in on hundreds of meetings with designers, and this customer was never part of the conversation,” said Mariah Chase, an industry veteran and the chief executive of Eloquii, an e-commerce site devoted to plus sizes. “Once I understood the sheer size of the population and the dearth of merchandise, it blew my mind.”

A 2016 study in the International Journal of Fashion Design, Technology and Education found that the average American woman wore a size 16 or 18. Yet annual spending on larger-size apparel accounts for only 16 percent of the $112 billion market in the United States because the inventory was not available.

Underserved market

“We’re getting bigger, but the business hasn’t gotten bigger,” Marshal Cohen, a retail industry analyst at the NPD Group, said.

That has begun to change. Spurred by an underserved market, along with a heightened emphasis on inclusiveness in the fashion industry, new retailers are sensing an opportunity. E-commerce businesses that rent, as well as sell, larger sizes have grown. With some focusing on moderately priced clothes and others concentrating on the designer market, these sites are finding an eager audience. Social media influencers like Jordyn Woods and Tess Holliday and actresses like Rebel Wilson and Chrissy Metz have also raised the profile of this market.

Retail giants are also expanding their presence in this market. In March, for example, Walmart acquired Modcloth, an e-commerce site that sold clothing in a range of sizes. Other e-commerce sites, like Stitch Fix, have also begun to offer larger sizes. But industry experts say large retailers lack the personal touch that shoppers seek.

“While Walmart and Amazon could be formidable competitors, this customer wants a company that understands her, and isn’t just selling to everyone,” Cohen said.

So some retail startups are trying to meet those demands. Christine Hunsicker, a tech entrepreneur, and Jaswinder Pal Singh, a computer science professor at Princeton, started Gwynnie Bee, a subscription-based clothing rental service.

“We became interested in apparel because of the size of the market and the need,” Hunsicker said.

In the Gwynnie Bee model, women who wear sizes 10 to 32 receive regular shipments of clothing. Once it’s worn, no laundering is required; clients simply return the options to the company for a fresh selection. If the customer loves an item, she can buy it, Hunsicker said.

In contrast, Eloquii is a reincarnation rather than a startup. The company was originally a brick-and-mortar retailer owned by the Limited, which, despite protests from a loyal customer base, shut down the brand in 2013, Chase said.

The founder and chairman, John Auerbach, who has had a number of e-commerce positions, bought Eloquii’s assets from Sun Capital in 2013, including intellectual property and the customer list. Chase joined the same year. The company has already been through two rounds of venture capital financing, and now has backing of close to $40 million, Chase said.

Pop-ups, bricks and mortar

Most of these businesses are focused on online customers, but some are experimenting with physical stores. Eloquii has opened three, in Chicago; Columbus, Ohio; and Washington. Two of them are pop-ups.

Most of the companies do not yet offer intimate apparel, although Eloquii plans to offer lingerie in the future.

To reach that market, Deborah A. Christel, a co-author of the study on women’s sizes, left her position as an assistant professor at Washington State University to start a company that would encompass all sizes for lingerie.

Christel said her company, Kade & Vos, would begin selling next summer. “It’s my hope that one day, women’s clothes will just be women’s without referring to plus size,” she said.