"Brands have recognized that second-hand market isn't going anywhere," said Fashionphile founder Sarah Davis. "This isn't a new, fun way to sell, but this is something your grandma did."

"I felt like, 'How long can Sephora be the only player in town?' asked Skyn Iceland founder Sarah Kugelman. "There's obviously a huge market opportunity, and for me it was obvious that Ulta was the most logical business to start to nip at their heels. Luckily, I was right."

"We live in a world where 30% of American women have all of the choice in the world, and 70% have very few options," Universal Standard co-founder Alexandra Waldman said. "So it was kind of a no-brainer where to start."

Josh Kilmer-Purcell and Brent Ridge joined the Glossy Beauty Podcast to talk about starting the business with "less than zero" dollars, cold calling department stores and their interest in investment considering the very ripe beauty M&A scene.

"I don't think I'm unique as a consumer, I think I'm a really average Joe consumer. So my intuition is that a lot of the things I like and are normal to me are also normal to 90 million other millennial shoppers in the United States."

Russell joined the Glossy Beauty Podcast to talk about the product's numerous prototypes, her company's surprisingly smooth relationship with Amazon and plans to enter the U.K. in 2020.

Launched in 2012, Fleur du Mal is applying all the strategies of a small brand looking to challenge a more established industry giant that's on the ropes, creating a lot of web content and tapping social media influencers to get consumers interested in the brand. Along the way, it's avoiding...

Gargiulo joined our show to talk about how she started a single-product brand before it was the norm, her Asian market distribution strategy and the pressure to make sure her brand's second product just as much of a hit as her first.

On the Glossy Podcast, Kahn discussed her career path from Marc Jacobs to DTC fine jewelry, the company's use of crowdsourcing to steer product development and its plans for international expansion.