Olaplex: What It Is, How It Works & Which Numbers to Use

What Is Olaplex?

Olaplex is a professional and consumer hair care brand built around a single patented active compound: bis-aminopropyl diglycol dimaleate (BADGD). Launched in 2014, it was the first product to commercially demonstrate that a small molecule could enter the hair shaft during a bleach service and reconnect the disulfide bonds that bleach breaks. It created the now-crowded bond-builder category.

The system is organized around numbered products. The number does not indicate potency or a recommended sequence for daily use — it reflects the product's intended step in the salon or at-home repair protocol.

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The Active Ingredient: Bis-Aminopropyl Diglycol Dimaleate

BADGD is a bifunctional molecule — meaning it has two reactive ends. Each end contains a maleate group that can react with a free thiol group (–SH), which is what remains on a cysteine amino acid residue when bleach has broken its disulfide bond.

The reaction:

When bleach (hydrogen peroxide at high pH) cleaves a cystine disulfide bond (–S–S–), it leaves two free thiols (–SH). BADGD diffuses into the cortex and each of its two maleate ends reacts with one free thiol, forming a new cross-link:

–SH + maleate–(spacer)–maleate + HS– → –S–maleate–(spacer)–maleate–S–

The result is a new bridge between two previously separated protein chains. This is not the same as restoring the original cystine disulfide bond (the bridge is now longer and chemically different), but it restores cross-linking density and, with it, tensile strength.

What makes BADGD special compared to earlier conditioning agents is its molecular size and solubility — it is small enough to diffuse through the cuticle and into the cortex, and its bifunctionality means a single molecule does the bridging work of reconnecting two protein chains.

A 2025 study published in Pharmaceuticals (Basel) characterizing novel hair repair agents found that a research compound (APA) formed more efficient bis-adducts than BADGD, showing the ingredient space is still evolving — but also confirming the fundamental maleate chemistry is independently validated.

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The Olaplex Product Range: Which Numbers Do What

Professional Steps (Salon Only)

No. 1 — Bond Multiplier Applied in the salon directly to dry hair before or mixed with the bleach or color formula. Contains the highest concentration of BADGD. The molecule works during the bleach service itself, cross-linking bonds as they are broken. This in-process application is the most evidence-backed use case.

No. 2 — Bond Perfector Applied after rinsing the bleach or color in the salon, before shampoo. Continues the bond restoration process and helps stabilize newly formed cross-links.

At-Home Treatment

No. 3 — Hair Perfector The consumer star product. A pre-shampoo treatment containing BADGD at a lower concentration than the professional steps. Applied to damp hair, left on for 10 minutes minimum (up to overnight for severely damaged hair), then shampooed and conditioned out. It is the entry point for most consumers and the most widely reviewed Olaplex product.

Protocol for No. 3:

1. Shampoo hair, towel-dry to damp (not soaking).
2. Apply No. 3 generously from mid-length to ends; roots if needed.
3. Leave on 10–90 minutes (longer for more damage).
4. Rinse thoroughly.
5. Shampoo with No. 4, condition with No. 5.

Daily Care Range (No. 4–8)

These products contain lower levels of BADGD as a background ingredient alongside conventional haircare actives. They function primarily as a high-quality shampoo, conditioner, moisture mask, bond smoother, and hair oil — with the bond-maintaining chemistry as an ongoing benefit rather than the primary repair mechanism.

No. 0 — Intensive Bond Building Treatment

Newer addition; applied before No. 3 for an amplified repair session. Targets severely damaged hair that needs more than No. 3 alone.

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What Olaplex Does and Doesn't Do

Does:

• Reconnects broken disulfide bonds inside the cortex
• Improves tensile strength and elasticity of chemically damaged hair
• Reduces mechanical breakage in over-processed hair with consistent use
• Works cumulatively — improvement compounds over multiple applications

Doesn't:

• Condition, smooth, or add shine on its own (pair with No. 5 for conditioning)
• Reverse severe structural damage from catastrophic over-processing
• Eliminate the need for heat protectant
• Work as a surface treatment — it does not coat the hair

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The Evidence: How Strong Is It?

The honest evidence picture:

Mechanistically strong: The maleate-thiol reaction chemistry is well-established organic chemistry. BADGD's ability to form adducts with cysteine has been confirmed in independent peer-reviewed research (including the 2025 Pharmaceuticals study).

In-house / brand-funded tensile data: Most published efficacy data for BADGD specifically comes from Olaplex-funded studies. Independent tensile testing from hair scientists (see Lab Muffin Beauty Science, published analyses) broadly confirms the bond-building mechanism is real.

No large independent RCTs: There are no independent large-scale randomized controlled trials comparing Olaplex to a placebo or competitor in human participants over time. The evidence base is mechanistic + in vitro + brand-funded clinical testing. This is common in cosmeceutical hair science — the research pipeline lags the commercial market.

Bottom line: The mechanism is scientifically credible and the product category is validated by independent research on the chemistry class. It is not a marketing-only claim.

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Who Should Use Olaplex

Most beneficial for:

• Hair that undergoes regular bleaching (highlights, full bleach)
• Chemically relaxed or permed hair
• Heavily color-treated hair with noticeable brittleness or porosity
• Anyone recovering from an over-processed chemical service

Still useful for:

• Regular heat tool users (flat iron, curling wand daily)
• Color-treated hair that is not bleached

Least benefit:

• Healthy virgin hair with no chemical or thermal history — there are fewer broken bonds to reconnect, so the impact is subtle

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How Olaplex Compares to K18 and Other Bond Builders

Full comparison including Wellaplex: Olaplex vs. K18 vs. Wellaplex: Which Bond Builder Wins?

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Common Questions and Myths

"Olaplex contains formaldehyde." Olaplex does not contain formaldehyde or formaldehyde-releasing ingredients. The brand published full ingredient lists and safety assessments confirming this. Formaldehyde concerns in hair products relate to certain keratin smoothing treatments — not bond builders.

"You need to use all nine steps." No. The numbers are not a routine to follow sequentially at home. Most home users need only No. 3 (repair treatment), plus No. 4 and No. 5 (shampoo and conditioner) if they like the format. The professional steps (No. 1 and 2) are used in salons during services.

"It won't work on natural / unprocessed hair." It is safe for all hair types and textures. For healthy unprocessed hair, the observable benefit is lower — but it is not harmful.

See also: Bond Builders Explained: How They Repair Damaged Hair