Personalization is central to Birchbox Inc.’s operations–for its subscription boxes and on its website.

On Birchbox.com, a consumer can sign up for a personalized, monthly subscription box that contains five sample-size cosmetic products tailored to her ‘beauty profile,’ which is where a shopper completes a questionnaire about her  skin type, hair type and other beauty preferences. After trying the product, a consumer can go to Birchbox’s website and order full-size versions of what was in her box, as well as shop for products from about 800 brands. The e-retailer declined to provide a specific SKU count.

The beauty e-retailer says it makes 65% of its revenue from monthly customer subscriptions and 35% from non-subscription products sold on Birchbox.com. The retailer’s web sales grew an Internet Retailer-estimated 21.0% in 2017 over 2016, according to Top500Guide.com. The retailer declined to give a specific sales number.

After a shopper signs up on Birchbox.com for an account, even if she hasn’t bought a subscription box, she will start seeing personalized content on the homepage, such as product recommendations and recently viewed products. But a personalized beauty profile is only available after she orders a $10 monthly subscription box, the e-retailer says. Once she subscribes, she can update her beauty profile at any time under the “Your Beauty Profile” drop-tab of her account.

“We’re changing customers’ experience with beauty and helping them shop for beauty in a way that’s more digestible with personalization,” says Meredith Schwartz, Birchbox’s vice president of product.

When a Birchbox subscriber comes to the homepage, she will see a section displaying her current Birchbox contents, which includes the products that came in that box and an explanation for why those products were selected for her. She can then go in and add more details about which products she liked and which she didn’t to further influence what Birchbox selects for her next delivery.

“In my personal Birchbox, I had this hair mousse that’s good for my fine hair, and this specific primer came in my box because I like organic products,” Schwartz says. “It’s tailored to who I am and relevant to me. It doesn’t feel like a random experience.”

As a consumer moves down the homepage, Birchbox displays carousels with the shopper’s previously browsed products, previously purchased products and products recommended around the shopper’s beauty profile. “When she browses products, that behavior will greatly influence what she sees,” Schwartz says.

Birchbox built its personalization system in house so it can continue to update and make new iterations on it, Schwartz says. An in-house operation allows the e-retailer to have unlimited flexibility in what it shows the shopper, she says.

But the challenge for Birchbox is ensuring its products remain relevant to its customers.“We have so many products and we want to give people things without them having to think about it too hard,” Schwartz says. “Even if we know a product is perfect for them, we want them to know why while being upfront about how we’re using the beauty profile information.”

As a shopper browses further into Birchbox’s site, she will see items related to what she’s previously interacted with. For example, if she looked at a lipstick, she could see a lip balm recommended to her that could be purchased with it.

On product pages, Birchbox does what Schwartz calls, “subtle personalization. When it doesn’t feel like we’re driving something at them, and it’s natural to the experience,” she says.

Customers post reviews of products—some products have hundreds or several thousand reviews—so to find the most relevant ones, Birchbox allows shoppers to sort the reviews by ‘My Profile’ to get a sense of what a shopper with a similar beauty profile might like or dislike about a product. Customers can also filter reviews written by reviewers by their skin type, skin tone, hair type, hair color and age.

“I can see reviews based on my own concerns, like sensitive skin or fine hair,” Schwartz says. “I can get a really good sense of a product from actual people who have used these things.”

Birchbox’s mobile web site operates with these same features. Its app, however, is tailored toward its most loyal, long-term shoppers, the e-retailer says. While it presents recommended products and shows the monthly subscription box details, the app also offers relevant content and articles to the shopper. The app is content-focused while the website is e-commerce focused, Schwartz says.

“We know that personalization is so important to Birchbox, and we want to make sure it’s at every touchpoint,” Schwartz says.

Viking Global Investors last week agreed to invest $15 million into the beauty retailer, CEO and co-founder of Birchbox Katia Beauchamp confirmed to Recode. “We are prioritizing product innovation, the evolution of our digital experience and scaled partnership opportunities,” Beauchamp said, regarding the investment. Birchbox’s other investors—including venture capital firms Accel Partners and First Round Capital—are getting wiped out and are expected to walk away with nothing, Recode reported. Since its 2010 founding, Birchbox had raised nearly $90 million in financing from investors.

Birchbox is No. 204 in the just-released Internet Retailer 2018 Top 1000.