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Cystine

Good

Humectant

Cystine description

Cystine is an amino acid that offers potential hydration and skin barrier benefits.

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Peer-reviewed, substantiated scientific research is used to assess ingredients in this dictionary. Regulations regarding constraints, permitted concentration levels and availability vary by country and region.

Ingredient ratings

Best

Proven and supported by independent studies. Outstanding active ingredient for most skin types or concerns.

Good

Necessary to improve a formula's texture, stability, or penetration.

Average

Generally non-irritating but may have aesthetic, stability, or other issues that limit its usefulness.

Bad

There is a likelihood of irritation. Risk increases when combined with other problematic ingredients.

Worst

May cause irritation, inflammation, dryness, etc. May offer benefit in some capability but overall, proven to do more harm than good.

unknown

We couldn't find this in our ingredient dictionary. We log all missing ingredients and make continuous updates.

Not rated

We have not yet rated this ingredient because we have not had a chance to review the research on it.