K18 and Olaplex Are Both Top-Tier Bond Builders—Here's How to Pick the Right One for You

Woman in blue T-shirt holds long black ponytail

Aneta Holehesh / Stocksy

In today's world of bond-building hair treatments, there is no shortage of products to help you achieve stronger, smoother, and shinier hair. But that wealth of options means it can be harder to suss out which ones will help you achieve your hair goals.

So we decided to dive into the benefits of two of the most popular bond-builders on the market: K18 and Olaplex. We tapped cosmetic scientist Xi Huang, Ph.D., board-certified dermatologist Kunal Malik, MD, Olaplex chief scientist Lavinia Popescu, and K18's Casey Yee and Cassondra Kaeding to learn more about each brand and its products. Keep reading for everything you need to know.

Meet the Expert

What Are Bond Builders?

Bond builders are formulated to repair hair that's been damaged through heating, bleaching, coloring, and other potentially harmful processes. They repair and strengthen hair from the inside out, Malik says.

There are many different restoring formulations for dry and damaged hair on the market, and most of the patented technologies claim to repair hair by reconstructing and repairing disulfide bridges or bonds within keratin, Huang tells us. Keratin is a fibrous protein in the hair that contains disulfide bonds that make hair strong and flexible.

"When hair is damaged by chemical treatments such as coloring or perming, the disulfide bridges in the keratin proteins become damaged or broken, which can lead to breakage, split ends, and other forms of damage," says Huang.

What Is Olaplex?

Olaplex uses an ingredient called bis-aminopropyl diglycol dimaleate to repair damaged disulfide bonds and restore the hair's strength and elasticity. "This helps reduce breakage and improves the overall health of the hair," Huang says.

Olaplex is designed to work on all hair types, but since curly hair has more hair bonds, Popescu says it's even more important for people with curly hair types to use bond-building products. "People can use Olaplex daily as part of their everyday hair routine, in accordance with the directions on each product," says Popescu.

What Is K18?

K18 uses a patented technology called bioactive peptides, which penetrate the hair shaft, attach themselves to damaged proteins, and form a protective layer around them. "This helps to strengthen the hair and prevent further damage," Huang explains. "These peptides are short chains of amino acids that can penetrate the hair shaft. Bioactive peptides bind to the damaged keratin proteins and repair them from the inside out."

K18 works on all hair types. "Everybody experiences hair damage to some degree—from color, chemical services, bleach, etc.," Kaeding says. "And it's not just in the salon—damage is ongoing and happens every day from simple actions like washing, styling, and UV and environmental exposure."

Kaeding points out that consistently treating hair and repairing damage leads to healthier, stronger hair over time. "We recommend using the K18 Leave-in Molecular Repair Mask for the first four to six consecutive washes and then as needed," she says.

How They Compare

The Science

Both K18 and Olaplex work by repairing the internal structure of the hair. "K18's bioactive peptides bind to damaged keratin proteins, while Olaplex's bis-aminopropyl diglycol dimaleate forms new bonds with damaged disulfide bonds," Huang says. "These treatments can help to improve the strength, elasticity, and overall health of the hair, but it's important to note that they are not a permanent fix for damaged hair."

According to Malik, both treatments can be effective at treating and preventing hair damage. "The K18 Leave-in Hair Mask contains peptides that can be very beneficial for hair and penetrate the hair shaft deeply to reverse damage and support growth," he says. "The peptide in the K18 is very similar in structure to the natural proteins found in hair—keratin—so it is an easily recognized peptide by the hair and can boost moisture and promote thicker hair."

Meanwhile, "Olaplex contains a proprietary ingredient that finds and repairs broken disulfide bonds in the hair shaft," he says. "Both will repair and restore hair health over time."

In-Salon Treatments

K18: In the salon, "the K18 Molecular Repair Service consists of the K18 Pro Mask and Pro Mist—both powered by the K18PEPTIDE," Kaeding says. The Pro Mist is designed to strengthen your hair's defenses before any potentially damaging chemical services, while the Pro Mask is on cleanup duty, repairing any damage that occurs during those services. "You can use them before and after color or chemical services, or they can also be used together as a stand-alone treatment," Kaeding says.

Olaplex: In a salon, Olaplex offers the Olaplex Stand-Alone Treatment, which is performed by a licensed professional and uses the brand's bond-building technology to repair and protect hair of all types and textures. It does this by relinking damaged disulfide bonds. "The Olaplex Stand-Alone Treatment can be used independently of a service and works on hair even if it has not been chemically treated," Popescu says. The process involves two steps: First, the Olaplex No.1 Bond Multiplier is applied, which reinforces the hair's strength and structure and can also mitigate some of the breakage that normally occurs during chemical services. The next step is the Olaplex No.2 Bond Perfector, which repairs damaged disulfide bonds. It can also be used by itself to strengthen the hair.

At-Home Use

K18: "The K18 Leave-in Molecular Repair Hair Mask ($75) is available in a smaller size for an at-home treatment," Kaeding says. "With hair damage happening at all times, it is important to ensure my clients are reversing this damage at home before any service."

Olaplex: Olaplex offers 11 products designed for at-home use, all of which utilize the company's bond-building technology to protect and care for hair. These include:

Picking the One for You

Part of the reason why K18 and Olaplex are so popular is that the products work for people with all different hair types and textures. The main requirement is that you're looking to strengthen and repair damaged hair.

"K18 is for everyone with hair damage—and everyone has some level of damage, whether it be from chemical services, styling, washing, or the environment," Kaeding says. And the same goes for Olaplex: "Disulfide bonds are broken by everyday stresses all the time, resulting in damage, even in virgin, low-maintenance hair," Popescu says.

To figure out which treatment is best for you, it's a good idea to speak with a hair expert, such as a board-certified dermatologist. Keep an eye out for adverse reactions, too. "Watch out for signs of scalp irritation, itching, or rashes as that may signify allergic reactions to one of the ingredients in either treatment," Malik says.

The Final Takeaway

If you're looking to repair damaged hair, both K18 and Olaplex are worth a try. The products work a bit differently from one another on a scientific level but accomplish the same goal: Repairing hair that has been damaged through everyday stressors like washing, coloring, bleaching, and styling.

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