MILAN (Reuters Breakingviews) - At the beginning of the 2019 documentary “Chiara Ferragni: Unposted”, the Italian Instagram star enters a tattoo parlour to get her nipple pierced. The camera lingers on her picture-perfect yet grimacing face while the job gets done. Sharing such personal life details, usually mixing elegance and fun, has won the fashion influencer 21 million followers and collaborations with Dior, Lancôme and others. Now Ferragni, 33, is considering a stock market debut to monetise the clothing-to-lifestyle persona she has built over a decade, according to a September interview with an Italian newspaper. An initial public offering in Milan, where she resides, would be a publicity coup for Borsa Italiana’s boss Raffaele Jerusalmi. But it would also test the staying power of the “influencer” business model. Social media celebrities have been a key plank of fashion houses’ marketing strategy. By building a reputation, they can promote a certain look to adoring Instagram fans, at a price. Brands typically devote some 10% to 20% of their promotional budget to such marketing, for a total of $6.5 billion in 2019, a nearly fourfold increase since 2016, according to Influencer Marketing Hub. Some global icons have already built brand empires. Barbadian pop star Rihanna’s LVMH-backed Fenty Beauty cosmetics generated 500 million euros in sales a year after launch. Last year she won Bernard Arnault’s support also for her fashion label. And perfume maker Coty agreed to pay $600 million for 51% of reality-TV star Kylie Jenner’s make-up business. Ferragni’s listing wouldn’t be in that league. She hasn’t specified which of the three companies she controls would go to market, or when. Sisterhood, which manages her marketing campaigns, reported revenue of 11 million euros last year, according to Italian press reports. Bundled with fashion business Serendipity and the TBS Crew, which owns Ferragni’s blog “The Blonde Salad”, they generated some 20 million euros of 2019 sales. At the 4 times sales multiple that Prada shares fetch, Ferragni’s group could be worth 80 million euros. It would be tiny, but likely the first IPO to feature a one-person brand solely built on web self-promotion. As the pandemic forces companies to reduce marketing costs, however, some are questioning the influencer model. Investors, too, will need to be convinced that digital businesses built on pretty faces are more than skin-deep.