Ingredient review
Bis-Glyoxyloyl Cystine
INCI: BIS-GLYOXYLOYL CYSTINE
A bond-repairing ingredient that helps strengthen hair from within, similar to the active in Olaplex.
In plain English
Bis-glyoxyloyl cystine is a lab-made molecule that works like a hair repair glue. It targets broken disulfide bonds inside the hair shaft—the same bonds that break from chemical treatments, heat styling, or UV damage. By reconnecting these bonds, it helps restore strength, elasticity, and smoothness without coating the hair surface.
Review score
Safety, usefulness, and evidence
Potentially useful with some tradeoffs
The evidence base is useful, but some claims depend heavily on the formula.
Risk flags are low for most users, though the finished product can still irritate.
- Source
- synthetic
- Evidence
- moderate
- Irritation
- low
- Clogging risk
- low
Quick decision guide
Useful, but context matters
Bis-Glyoxyloyl Cystine is generally a lower-concern ingredient when the full formula suits your skin.
Plain-English read
Treat this as a practical screening step before you compare products that contain this ingredient.
- Step 1Start with the score, then check the irritation and clogging risk before judging Bis-Glyoxyloyl Cystine.
- Step 2Use the "Best for" and "Use caution if" sections to match the ingredient to your skin, not just to a marketing claim.
- Step 3If a product stings, breaks you out, or worsens irritation, judge the finished formula and stop using it even if the ingredient scores well.
Score terms in plain English
Irritation risk
lowLess likely to sting, burn, or bother most users, though sensitive skin can still react.
Clogging risk
lowLess likely to feel heavy or contribute to clogged pores for most skin types.
Evidence level
moderateThere is useful support, but formula details and claim strength still matter.
What it is
A synthetic derivative of the amino acid cystine, designed to penetrate the hair cortex and reform broken disulfide bonds.
How it works
When applied to damaged hair, bis-glyoxyloyl cystine reacts with the free thiol groups left behind by broken bonds. It forms new, stable disulfide bridges inside the hair fiber, restoring structural integrity and improving tensile strength.
Pros
Targeted bond repair
Specifically reconnects broken disulfide bonds inside the hair shaft, not just a surface coating.
Improves hair resilience
Regular use can reduce breakage and make hair feel stronger and more elastic over time.
Cons and cautions
Requires correct pH
The bond-repair reaction is pH-dependent; if the product isn't formulated properly, it may not work effectively.
Not instant
Visible results typically require multiple applications; it's not a one-and-done fix for severe damage.
Best for
- People with chemically treated or heat-damaged hair
- Anyone looking to strengthen fragile or brittle hair
Use caution if
- Those with unprocessed, healthy hair who don't need bond repair
Usage tips
Safety summary
Considered safe for topical use on hair and scalp at typical concentrations. Rare reports of mild scalp irritation in sensitive individuals.
Research notes
Clinical studies and in-vitro tests show bis-glyoxyloyl cystine can significantly increase hair tensile strength and reduce breakage after repeated chemical damage. More independent peer-reviewed research is needed.
Common label clues
- Typical concentration
- 0.5% to 2% in leave-in or rinse-off formulas
- Regulatory status
- Approved for cosmetic use in the EU, US, and other major markets; no known restrictions.
- Common uses
- Hair treatments, Shampoos, Conditioners, Hair masks
- Environmental note
- Synthetically produced, so it does not rely on animal or plant harvesting. Biodegradability data is limited.
Good to know
- Bis-glyoxyloyl cystine is the key active in several popular bond-repair hair products, including Olaplex No. 3.
- It is heat-activated in some formulations, so applying heat may enhance penetration.
Common questions
What is Bis-Glyoxyloyl Cystine in beauty products?
Bis-glyoxyloyl cystine is a lab-made molecule that works like a hair repair glue. It targets broken disulfide bonds inside the hair shaft—the same bonds that break from chemical treatments, heat styling, or UV damage. By reconnecting these bonds, it helps restore strength, elasticity, and smoothness without coating the hair surface.
What does Bis-Glyoxyloyl Cystine do in a beauty product?
When applied to damaged hair, bis-glyoxyloyl cystine reacts with the free thiol groups left behind by broken bonds. It forms new, stable disulfide bridges inside the hair fiber, restoring structural integrity and improving tensile strength.
Is Bis-Glyoxyloyl Cystine safe for most people?
Considered safe for topical use on hair and scalp at typical concentrations. Rare reports of mild scalp irritation in sensitive individuals.
Who should be careful with Bis-Glyoxyloyl Cystine?
Those with unprocessed, healthy hair who don't need bond repair
Research sources
Ingredient reviews are educational and are not medical advice. Patch test new products and ask a licensed clinician about persistent irritation, allergies, pregnancy-specific questions, or diagnosed skin conditions.