Olaplex was not started by a hairstylist. It began in California in 2014, when Dean Christal met two materials scientists at UC Santa Barbara, Craig Hawker and Eric Pressly, and got his first sample out of Pressly's garage. The idea was a single patented ingredient, bis-aminopropyl diglycol dimaleate, designed to reconnect broken disulfide bonds in hair, and every product the brand makes contains it. It started as a salon-only treatment that colorists passed around by word of mouth, which is why the numbers on the bottles still read like steps in a salon service. Olaplex bonding oil is number 7, a concentrated, very light oil that works as a heat protectant and cuts frizz. Two drops through damp or dry ends is enough, and more will make fine strands look greasy. The rest of the first row covers the other leave-ins. The Shine Serum is a two-in-one oil and hydrating mist, the number 9 Bond Protector is a weightless serum that also guards against heat, and the number 6 Bond Smoother is a styling cream that keeps frizz down for up to 72 hours. I went deeper on a related idea in Color Wow, the Bottles Behind the Hype. I went deeper on a related idea in What Olaplex No.3 Turned Into, and the Numbered Shelf Around It.

The second row is the system the oil was designed to finish. Number 0 is an intensive treatment that primes hair, and number 3PLUS is the pre-shampoo mask, the step most people start with. Number 4 is the shampoo, here in the version for fine hair, and number 5 is the conditioner for medium hair. Used together once a week, they are the closest thing to a salon bond treatment you can do in your bathroom. Leave the 3PLUS on for the full three minutes the brand recommends before you wash. I kept the order on a sticky note by the sink for the first few weeks, because the numbers are easy to mix up.

Olaplex is not the only brand working on bonds. K18 was founded in San Francisco by Suveen Sahib and Britta Cox, and its peptide builds on research by a Portuguese team that scanned the hair genome for a peptide to reconnect broken keratin chains. The K18 oil is the one I reach for on bleached ends. Shu Uemura, founded by a Japanese makeup artist who worked in Hollywood, makes the Essence Absolue oil with camellia for shine. L'Oréal Professionnel's dual oil is a bi-phase bond builder, and Kérastase Première is a high-shine oil that protects against heat and split ends. What I would skip is layering two of these at once. Pick one oil and use it sparingly.

Put the oil on last, after any cream or serum, and only on the lengths. On damp hair it helps with blow-drying, and on dry hair it tames flyaways. If your hair is very damaged, do the numbered steps weekly and let the oil handle the daily polish. It is a lab-born brand, so the instructions are the point.