The reason he has amassed so many followers is only partly due to his role as the head of Balmain, a 70-year-old French fashion house that seemed stuck in the past until Rousteing’s arrival. The other part is all those gym videos, celebrity snaps, and selfies.

“I’m young, I’m black, I’m a designer, I have famous friends, but I also eat hamburgers and have both feet on the ground,” Rousteing told WWD (paywall). “It’s real life and reality always excites people.”

Indeed, the key to Instagram’s attraction for businesses is that it allows a personal connection, or at least the feeling of one, between the business and those it wants to reach. The grainy, unscrubbed, behind-the-scenes images mixed in with the polished ones offer a sense of intimacy. Creating this intimacy is what Rousteing is good at—not because he’s a master marketer, though he may be, but because at 28, he’s a true millennial. Sharing details of his life in public is just what he does.

That makes him rare among the upper echelon of fashion designers (many of them much older than him). You don’t see Dries Van Noten posting shirtless photos on his Instagram page. Hedi Slimane’s account exists solely to direct people to his website. Phoebe Philo famously said the height of chic is when you “don’t exist on Google.”

These designers—who all grew up before Instagram existed—are missing a huge opportunity. In the fashion world, Instagram and influence go hand-in-hand. The platform has more than 300 million active users, and being image-based, it’s the ideal social network for the fashion industry to reach its fans. Brands seem to create their ads for Instagram now, rather than glossy magazines.

At recent fashion event filled with luminaries such as designer Jean Paul Gaultier and Vogue International editor Suzy Menkes, Instagram’s co-founder, Kevin Systrom, pointed to the Instagram success of the New York-based label Public School as evidence of the platform’s efficacy for those seeking fashion-world recognition.

Rousteing himself told the Telegraph in January that he considers Instagram “the new high-street window” for a fashion brand. “You can actually be part of the dream,” he said. “It’s not only available to 10 people on the front row.” (Back then Rousteing had only a measly 928,000 Instagram followers.)

Rousteing’s numbers are dwarfed by the likes of US reality TV star Kim Kardashian, who has 27.3 million followers and counting. In Quartz’s fashion Instagram universe, he falls right on the line between being under the radar and part of the mainstream. 

But to put Rousteing’s million followers in perspective: On a daily basis his photos connect with about as many eyes as Vogue magazine does each month. That’s influence. 

📬 Sign up for the Daily Brief

Our free, fast, and fun briefing on the global economy, delivered every weekday morning.