Cystine
A sulfur-containing amino acid. It supports hydration and joins a recovery complex. Well tolerated.
Evidence by route
Topical application
An amino acid that supports hydration. Safe.
- CIR Cosmetic Ingredient Review safety assessment
How to read tiers A–F
- BLimited evidence. One RCT or several controlled studies with limitations
Tolerability and safety
- Irritation potential
- Low
- Allergen risk
- Low
- Pregnancy
- Safe
- Suitable for
- Normal, Dry, Combination, Oily, Sensitive
About this ingredient
Cystine is an amino acid of two joined cysteine molecules, rich in sulfur. INCI: Cystine. In a formula it works as a conditioning agent: it is part of skin and hair keratin, supports the protein structure of the stratum corneum, and helps keep softness. It appears more often in hair products and strengthening care. Its standalone cosmetic activity is mild; it is a supporting component rather than a lead active with a marked clinical effect. Pregnancy safety. Topical use, low systemic absorption, no evidence of harm. It can be used during pregnancy and lactation. Tolerance. Irritation and allergen potential are low, suitable for sensitive skin.
Frequently asked questions
Is Cystine safe during pregnancy?
Cystine is considered safe during pregnancy at typical cosmetic concentrations. Systemic absorption through the skin is minimal.
What skin types is Cystine for?
Cystine suits: normal, dry, combination, oily, sensitive.
What is Cystine and what does it do in cosmetics?
A sulfur-containing amino acid.
What's the INCI name for Cystine?
The INCI name is Cystine.
See Cystine in a product composition right on the store page
The Evigrade extension adds an evidence panel to iHerb, Sephora, Druni and 12 more stores. This ingredient and every other one in the product show evidence-tier, allergen risk and pregnancy/lactation flags at a glance.
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