Private equity firm TPG Capital is nearing a deal to take a minority stake in skin care brand Rodan + Fields, sources familiar with the situation tell CNBC.

The business, which sells its products exclusively through a network of consultants, rather than through retailers, was founded in 2000 by Dr. Katie Rodan and Dr. Kathy Fields. It generated 2017 net revenue of more than $1.5 billion and grew at a rate of 40 percent.

Its sells skin care products under names like Redefine and Unblemish to treat skin through "dermatology-inspired skincare." Rodan and Fields are Stanford-trained dermatologists.

A valuation of the company could not be immediately determined.

The sources, who cautioned a deal could still fall apart, requested anonymity because the information is confidential. TPG declined to comment. Rodan + Fields did not immediately respond to a request for comment.

TPG's stake is one more affirmation of investors' increased confidence in direct sales business models. Today's iteration distinguishes itself from its predecessors like Avon Products, by extensive use of social media and infomercials.

Younique, a direct sales cosmetic company with a heavy social media following, was acquired by Covergirl-owner Coty in a deal reportedly valued at $1 billion.

The direct-sales model has taken a new power as skin care and cosmetic brands look for ways to sidestep the department stores they traditionally relied on, but which are losing foot traffic.

Rodan + Fields was acquired by Estée Lauder in 2003 and, at that time, its products sold in high-end department stores. In 2007, Drs. Rodan and Fields bought the company back from Estee Lauder. It relaunched as a consultant-based direct seller.

It has a network of more than 200,000 consultants and more than 2 million customers in the United States, Canada and Australia.

With TPG's investment, it expects to grow both domestically and internationally.