Birchbox co-founder Hayley Barna has stepped down as co-CEO. 

Barna launched the beauty subscription service in 2010 with her former classmate at Harvard Business School, Katia Beauchamp. Beauchamp's LinkedIn page has been changed to say "CEO" instead of "co-CEO."

"While we very much miss having her in the office each day, she will always remain an integral part of the company and will continue to be actively involved as an advisor and member of the Board of Directors," chief communications officer Claire Paull said in an emailed statement.

It's unclear what prompted Barna to step down. Reached by phone, Birchbox's director of PR and partnerships Jenna Hilzenrath declined to comment beyond the emailed statement.

In a previous interview with Inc., Barna said she and Beauchamp agreed to a set of terms early on about what would happen if one of their roles at the company were to change. 

"[It's] questions like 'What happens to your equity if you are no longer working full time at the business?'" Barna said. "It's almost like having a prenup before you get married."

At Birchbox, Barna was responsible for internal functions like technology, product development, and operations, while Beauchamp focused on external functions like PR and business development.

"We knew that to scale, we would have to divide and conquer," Barna said in the interview.  

Birchbox opened its first brick-and-mortar store in Manhattan's SoHo neighborhood roughly a year ago. The company's current subscriber base stands at more than 1 million, up from 400,000 in 2013. 

"[A]s we begin this next chapter, we're more focused than ever on growing quickly and strategically and reaching the 44 million U.S. consumers who are currently underserved by the $465 billion dollar global beauty industry," Paull wrote.

Birchbox has raised a total of $72 million from investors include Accel Partners, First Round Capital, and Viking Global Investors.