Ms. Glick, who when it came to her age would say only that she is in her early 40s, would not say whether MUA is in the black, but high profits do not seem to be the point. “We are not saving lives, but what we are doing is noble,” she said. “We allow consumers to connect to other consumers and gain knowledge, and that’s a noble thing.”

Top MUA reviewers have hundreds, even thousands of critiques under their pseudonyms, so if someone posts a one-word review (“awesome!”), or has only a few, then users are quick to flush them out. (One can’t start a review thread on the site without having more than 20 reviews, and ones that contain advertising or profanity are rejected.) The most prized recommendation comes from a “skin twin,” MUA-speak for a woman who mirrors one’s complexion and concerns. (Members may remain virtually invisible, or disclose the color of their hair and eyes, skin tone and type, and age.)

And now, MUA itself is getting a kind of skin twin — with a commercial edge. Bloom.com, a “social beauty store” that makes its official debut in August, will allow members to fill out a profile, including data about their skin, age and concerns. A search for a specific product, like mascara, will produce six recommendations, based on the reviews of 20,000 women who participated in focus groups or who are currently members. Soon, members will be able to see who recommended the products, and click that person’s reviews, before buying.

“The best recommendations come from women like you,” said Julie Mahloch, 42, who founded Bloom.com with Nick Hudson, 39, who worked for Boots for 12 years. She added: “My friend might have my best interests at heart, but probably not the same skin type or concerns that I do. We want to take it to the next level and, using the power of thousands of women, to match you based on a number of profile data points with women who are like you.”