In 2014, Sarah Lee and Christine Chang left their marketing jobs at L'Oréal to launch Glow Recipe, a modern Korean skin care brand, with just $50,000 in savings. One of two initial products, a watermelon mask, was inspired by their grandmothers, who'd rub watermelon wine on heat rashes during summer months in Korea. The mask quickly became a cult favorite, so the co-founders launched an entire line of watermelon products.

Lee and Chang say that creating a winning skin care formula comes down to texture, scent, and results. Customers respond well to novel textures--like bouncy and elastic gels--scents that resemble real fruit, and effects that appear overnight. The New York City-based company became profitable after three months of business (which allowed it to politely decline a Shark Tank investment in 2015), and its revenue has grown steadily ever since--252 percent in the past two years.

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Correction: An earlier version of this article misstated the percentage of Glow Recipe's total business that comes from its watermelon product line. It is 55 percent.