When Cortes' daughter was born in 2012, she stayed at home with the baby. "I was completely dedicated to my baby," she says. "I didn't take care of my skin. I didn't take care of anything." After reading an article about the multi-step Korean beauty routine, she fell into the Asian beauty product community — a cheerful corner of the internet where people swap studies about the efficacy of snail slime on wrinkles, buy their own pH strips to ensure their cleansers are appropriately acidic, and post pictures of their latest hauls from South Korea.

Last January, she started a blog, and befriended other Asian-skincare bloggers. Late one night, she and Jude Chao of Fifty Shades of Snail talked about their dream products. There were so many products out there, Chao complained, but none were the simple, well-formulated products they craved. Why couldn't someone make a serum with niacinamide (a form of B3 demonstrated to help skin elasticity and fade discolorations), but actually include 5% of it, the amount shown by studies to be the most effective?

Cortes offered to try. She took her DIY background and her scientific training — at the time, she worked at an at an environmental lab testing water quality — and started tinkering with a formula for what she dubbed Shark Sauce, after Chao's Reddit username. After testing the product — a mixture of niacinamide, licorice root (to fade dark spots), and sea kelp bioferment (a moisturizer and acne fighter) — Chao wrote a laudatory post about her results.

"I use [a product] in isolation for a couple of weeks to see if it's doing anything. The immediate effects of it were very soothing," said Chao. "You can tell when I don't use it: my skin feels different, and it looks a little more dead." Spending her twenties tanning left her with freckles and sunspots, but, "those things were going away so fast. Nothing else I used put that much of a dent, and this stuff was doing it in the first month. I'd wake up and have patches of them gone."

Cortes also wrote a post, and included her recipe. The response, in the comments of their posts and on the Asian Beauty Reddit, was deafening. People wanted Shark Sauce, and were willing to throw money at Cortes to get it.

Eventually, she started selling the product during nights and weekends. It was an immediate hit. Since opening the store in November, Cortes, working alone from her home in Fort Smith, Arkansas, has fulfilled thousands of orders for the $30 serum for customers from Singapore to Denmark. (Somewhat ironically, it has many fans in South Korea, home of the products that got Cortes into skincare). In the beginning, Cortes posted the times she restocked Shark Sauce. Customers far away from Arkansas, desperate to make the deadline, set alarms waking them up in the middle of the night. Another customer stopped driving and pulled over to restock using her phone. These dramatic measures were necessary: in the early days, the product sold out in seconds, often multiple times a week.

Sales grew as people started posting rave reviews of Shark Sauce. Cortes was making the product for people like her, consumers who embraced chemicals, science, and had an internet-provided education in cosmetic ingredients. She captured what people wanted but companies rarely provided: simple formulations, powerful ingredients, and most of all, transparency via listing active ingredient percentages — instead of another overpriced serum with filler ingredients and a drop of retinol. Shark Sauce spread throughout Reddit and the skincare blogosphere, spawning a thriving Instagram hashtag– featuring hundreds of artfully composed product routine photos featuring Shark Sauce, and reviews that tended toward religious zeal. "I'm half-convinced that [Cortes] must make each batch in a cauldron whilst chanting PIH [post inflammatory hyperpigmentation]-banishing spells, because this stuff is magical," one fan said on Reddit. "It seriously makes my skin look like I bathed in unicorn tears, distilled fairy sweat, or kitten laughter," another said on Instagram. "This magic potion delivered me from skin sin and exalted my ass straight to skin nirvana," wrote Coco Park, an esthetician and co-author of Korean Beauty Secrets.

The raves are nice, but sometimes stress Cortes out. "I am the worst person to describe Shark Sauce because I don't want to sound gimmicky," she says. Unlike products like, say, La Mer —"In a short time… skin looks virtually ageless" — she doesn't make any bold claims about the product. The description merely says it's a hydrating serum with ingredients that should help with hyperpigmentation. For Cortes, it's simple why people love Shark Sauce: the formula is straightforward, so they know what to expect. The serum was a challenge, both to herself and skincare companies: "If I can sit here and make this in my kitchen, why the heck is there not anything like this on the market?"

After frantically trying to keep up with the demand, Cortes quit the lab and started making Shark Sauce full time. She transformed a room in her house, tearing out the flooring, replacing everything with stainless steel and bought a fridge dedicated solely to ingredients. "It's as close to a lab as I can get in my house," she says.

It wasn't an easy transition. Cortes had to teach herself everything about running a business, from designing labels to ensuring products won't deteriorate while being shipped across the world. Shark Sauce's name has also caused grief — angry customers chastise her for using shark in the product. (She doesn't, if that was still unclear.) One excited customer had a friend drizzle it on their food after leaving her bottle on the counter.

Sourcing ingredients has also been a learning experience. In her early DIY days, Cortes tried to dupe French cult favorite Biologique Recherche Lotion P50, and wanted mandelic acid in her version for a similar exfoliating effect. It was surprisingly hard to find, but she eventually found pure mandelic acid powder on Ebay. "It came in a Ziploc bag that was not labeled, that had a weird leak in it," Cortes says. She threw it out and Googled why pure mandelic acid is so difficult to source. Turns out, it's is often used to make meth.

Now that Shark Sauce is her livelihood, people would understand if Cortes stopped posting skincare DIYs or stopped responding to comments about making Shark Sauce. But she doesn't plan to. "I still put out recipes and I still want to help the DIY community because I think this is important. People are afraid," she says. "It's not that different from food. You can go to a restaurant and get a steak, but you should also know [you can] buy a steak and cook it at home."

Cortes' blog has two recipes for Shark Sauce. Neither is the version sold in her store, but both provide the niacinamide base customers love, albeit in different ways: the initial version has more impressive ingredients, while the second has fewer ingredients but is more cosmetically elegant. And for the those who want the challenge of making it at home, she has simple advice: "Be careful," she says. "You have to respect what you're doing. It's not impossible, it just requires a lot of attention."

Kelly Dobos, a cosmetic chemist, agrees. "You have to be really careful making something at home because the product doesn't go through the rigorous amounts of safety testing like something made by a cosmetic manufacturer," she warns. She praised the Shark Sauce recipe, and its inclusion of parabens: "You want to to make sure you're using a good preservative system. Parabens are a good preservative, they have a long history of safe use in the cosmetic industry." Dobos also recommends following basic lab safety procedure: wearing gloves, safety glasses and being hyper-vigilant about avoiding cross contamination.

Cortes soon moved on from Shark Sauce, coming out with small line of products, including a facial oil and lip balm. Now, she's finishing a Vitamin C serum, but since Vitamin C products often destabilize in light and heat, shipping is difficult. So Cortes puts sample bottles through a series of tests. She throws them against a wall, down the stairs, and leaves them outside in 90-degree heat. And once she solves that problem, she'll end up in her favorite spot: back in her homemade lab, joyfully tinkering on her next challenge.