This Wildly Popular Beauty Buzzword Has Everyone Confused (2025)

I had a startling realization earlier this year while standing at my bathroom vanity. I’d just washed my hair using a bond-repairing shampoo and conditioner duo, followed by a bond-repairing hair gloss. I got out of the shower and used a bond-repairing leave-in conditioner followed by a bonding hair oil. Once my hair was dry, I hit it with a few spritzes of a bond-repairing dry shampoo. Every single one of these hair products was by a different hair-care brand. And every single one promised the moon on a string. Do you want stronger, healthier hair? Want to erase all signs of heat damage? Want to return your hair to its factory settings?

Olaplex, by all accounts, started this craze back in 2014, and bonding has now become the cornerstone of new hair-care launches from drugstore brands like L’Oréal, Tresemmé, Nexxus, Clairol, and Suave and prestige brands like Living Proof, Redken, K18, Epres, and so many more. When it finally clicked that my entire hair-care routine was a mixed bag of varying bonding claims, I was hit with a hundred different questions at once. Am I over-bonding my hair? If it took years of research and iron-clad patents for Olaplex to develop bond repair, how are drugstore brands doing it with common ingredients like citric acid? What kind of hair bonds are we even talking about here?

I’ve spent over 13 years reporting on hair-care science, and navigating the growing bond-care space has proved confusing even to me. But I knew who to call for answers. Ahead, the expert guide to hair-bond repair, with insight from materials scientist and Epres brand founder Eric Pressly, who helped develop Olaplex; cosmetic chemist Javon Ford; Lavinia Popescu, chief scientist at Olaplex; and Fraser Bell, vice president of advanced research at K18 Biomimetic Hairscience.

Before continuing on, a quick science refresher: Hair is made of protein—mostly keratin—and proteins are made up of groups of tiny little things called amino acids. A chain of 23 different amino acids is called a polypeptide. Proteins are very long molecular chains. Got it? Cool!

Let’s start with the basics: Your hair is made up of more than 23 amino acids and, therefore, protein. “The amino acids have little dots that you put on top of each other, like a Lego, and that creates the keratin structure,” Popescu says. “In the keratin structure, we have three main bonds: hydrogen, ionic, and disulfide.” She stresses there are other bonds in the hair, but the following are the most important to know for hair health:

• Hydrogen Bonds: “Hydrogen bonds are broken when your hair is wet. That’s what makes your hair malleable,” Ford explains. “So, you know how you can do wet styling to the hair? That’s the hydrogen bonds at play.” Your hair is more prone to breakage too when it’s wet because the hydrogen bonds are out of sorts, says Ford. Popescu adds that hydrogen bonds are also the weakest bonds in the hair—and the most abundant. “You don’t need to do anything else than to take out the water from the hair to reform. They reform by themselves,” she says. Hydrogen bonds are also impacted by heat styling.
• Ionic (Salt) Bonds: Responsible for a sizable chunk of hair’s strength, ionic bonds “are not very weak, but not strong” and “usually reform based on the hair’s pH,” Popescu says. Ionic bonds can break from high pH exposure from water or chemical treatments and reform with ingredients like citric and malic acid, which lower the pH and seal the cuticle. But both hydrogen- and ionic-bond repair is temporary—and easily removed. “With soap and water, you can take those away,” Pressly notes. “They’re not long-lasting, so it is a really confusing thing for the public.” Popescu agrees: “Some products claim to bond-repair, but they primarily work on these weaker bonds.”
• Covalent Bonds (Disulfide, Peptide): This is where Olaplex, K18, and Pressly’s Epres brand come into play. “Disulfide bonds are the strongest and most important bonds with hair’s structure; they hold the individual polypeptide chains together and help provide strength,” Bell says. Unlike hydrogen or ionic bonds, disulfide bonds can’t be repaired easily and require specific technologies and molecules to enter the hair’s cortex and relink them. “Disulfide bonds are so important because these are the bonds that really bring the strength of the hair and determine how strong the fiber is,” Popescu says. “If you don’t reform disulfide bonds, especially after a chemical treatment like color or bleach, the hair will break when you brush it and when you apply a flat iron.”

All three of these bonds are essential for hair’s overall health, but it’s important to understand the distinction between them to choose the right bond-repair product for your specific hair.

The cuticle is your hair’s protective outer layer, and when it’s healthy, it’s smooth and flat. Damage can lift some of the overlapping cells of the cuticle, leaving your hair brittle and prone to breakage. The cortex is the middle layer of your hair, and that’s where you’ll find the hydrogen and disulfide bonds.

Bond repair or bond building, put simply, is the act of relinking bonds in the hair that have been broken to help boost hair’s overall strength and resilience. “It’s a term that we came up with, but it’s not like a clinical term,” Pressly says, referring to his time as a developer of Olaplex. “It’s not like the FDA regulates what bond repair is.” And that’s the key point here: As long as a product repairs a bond—whether it’s hydrogen, ionic, or disulfide—it can hold bonding claims on the packaging. However, relinking disulfide bonds requires near alchemy and expensive patents, while patching up damage from wonky salt or hydrogen bonds can be as simple as choosing the right conditioning product. Nourishing ingredients like silicones and oils can indirectly help hair bonds by protecting the hair’s cuticle, but they’re not responsible for bonding. Pressly likens the difference between the two types of repair to a piece of paper and some tape. When you rip a piece of paper, you can patch it up with tape—but is it really, truly repaired? Relinking disulfide bonds is like fusing the paper back together.

“A lot of the more affordable brands aren’t even claiming to fix bleached hair. They do claim bond repair, but they don’t say exactly what the product’s addressing,” says Ford. “They’re not fixing hair damage by bleach or heat styling, because those are damages to disulfide bonds. They’re claiming just general bond repair, which is great for hair’s overall health.”

Olaplex holds the Bond Building Technology trademark, so you’re more likely to see words like “bond strength” and “bond repair” on competitors’ packaging. “The category started in my garage 12 years ago. We patented that technology, and then 200 companies came out quickly, none of which you’ve heard of, that all claimed to do that too,” says Pressly. “And most don’t exist now because they didn’t do it.” It’s also worth noting that Olaplex, Epres, and K18 all offer exclusive in-salon bonding treatments for more intense damage repair that can be coupled with bleaching or coloring services to help mitigate disulfide breakage.

Want to learn more about how the individual technologies work—from Olaplex, Epres, K18, and more—to hold bond-repair claims? Scroll through the gallery ahead.

“Optimal conditions for every hair-repair technology can differ, and the use of heat or application to wet hair can influence the performance. To repair at the source of damage, a technology needs to penetrate to the core of the fiber, and the penetration of some technologies can be assisted with the addition of heat or wetting of the hair,” Bell says. Some Olaplex products, like No. 0 Intensive Bond Building Treatment, can be applied on dry hair, while others, like No. 3 hair mask, should be applied on wet hair. Epres was designed to be applied on dry hair, and K18’s Molecular Repair Hair Oil is best applied on wet hair to reap the benefits of the patented peptide. Living Proof’s formula requires heat to activate the covalent cross-linking, so, essentially, read and follow your product’s instructions.

Did you know: Ford says that bonds in the hair are so small that they can’t be seen by most microscopes available today. Hair-care brands do have other ways of measuring the presence of bonds in the hair, but more times than not, the actual relinking of hair bonds can’t be witnessed by the human eye.

“Real repair should last through washes,” Pressly says. “At least five to 10 washes, depending on what you’re doing to it in between. If you’re flat-ironing your hair every time, then you’re doing new damage.” The disulfide bonds linked by the tech in Olaplex, Epres, and K18 will stay linked—until they are broken again by a chemical or color treatment. Products that rely on citric acid will need to be used more often, likely daily or at least every time you shampoo. “Citric acid is definitely rinsing out as soon as you wash it,” Ford notes. “It’s not like forming a bond-bond, because that’s just not how citric acid works.”

The cosmetic chemist notes that all these bond repairers, even the patented ones, are temporary. “You have to keep using the treatment; you just don’t have to use it as much once your hair starts to feel better,” Ford says. “But at the end of the day, it still isn’t a permanent fix. The only permanent fix is cutting your hair.”

“You can’t over-replace the disulfides—once you repair them, that’s the total amount that you have—but if you’re using other stuff that coats the hair, like proteins or peptides, then you can over-coat the hair,” Pressly says. Ford agrees and says you can overuse anything, even regular ol’ conditioner, but he’s not sold on the idea of protein overload—that is, overexposure to protein making the hair too rigid. “The whole discussion of protein overload is not fully accepted by science. Hair-care science in general is lacking. When you look on cosmetic-chemist forums, they’re like, ‘No. Protein overload doesn’t exist. Proteins are hydrating.’ But conventional wisdom, especially among stylists, is that proteins are drying.” Bell adds that K18, when used as directed, delivers only reparative benefits. “Hair that is damaged will have more available sites for the K18Peptide to provide repair to, compared to less damaged hair. Often, the impact from overuse of the product stems from overexposure to other cosmetic ingredients in products and less so around over-repair of hair," he says. The experts agree that hair products containing hydrolyzed proteins—that is, proteins that have been altered to be really tiny molecules—are generally safe to use without concern of overuse.

Popescu says the beauty of Olaplex’s bond-building technology is that it “doesn’t build up” and “can’t be overused.” You might recall some negative chatter about Olaplex’s products a few years back. There was a trend of leaving the No. 3 Hair Perfector in the hair overnight instead of for the recommended three to 10 minutes, which led to some users reporting that their hair felt damaged. Here’s the truth: “Within an hour, anything that’s gonna be absorbed by the hair is already absorbed,” says Ford. “At that point, keeping your hair wet [from the mask] and keeping the hydrogen bonds in flux, because your hair is still damp, can lead to damage.” So, again, follow the directions and see how your hair feels when you incorporate bond-building into your routine.

“It is absolutely safe to assume that most people have some level of broken bonds, especially those who regularly color or treat their hair with heat,” Bell says. “Whether it’s from frequent coloring, bleaching, or heat styling, these activities all contribute to the breakdown of the bonds and interactions that keep hair strong and healthy—which is why damage repair is key.” Unless you frequently change your hair color, Ford says most of us can probably get away with seeing nice reparative results from a citric-acid-based bonding product or standard deep conditioner. “But at the end of the day, a lot of hair stuff is purely aesthetic. It’s about how your hair feels to you, right?” he says. “So you can have a really good hair mask that makes your hair feel great. And then I know some people have used some of the bond-repair things and didn’t notice a difference because it didn’t feel conditioning enough."

Popescu says to do some research to find the right bond builder for your hair. “If consumers are looking for treatments, they should look to brands with proprietary technologies and brands that show testing for efficacy and safety,” she says. “My other advice is, if you like a brand and like the benefits and the end results, stay with that brand. You don’t have to change.” Ultimately, it’s about what makes your hair feel and look soft, manageable, shiny, and healthy—regardless of the price or patents. You can start your bonding journey here by shopping some of Bazaar editors’ favorite bond-repair products: