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Cystine

What Cystine is & what it does

Cystine is an amino acid formed from two linked cysteine molecules, used in cosmetic formulas as a conditioning and skin-supporting ingredient. In skincare and sunscreen products it is typically present at low levels to support the formula rather than as an active sunscreen filter. A notable property is that its sulfur-containing structure is also a natural building block of keratin, the protein found in hair and the outer skin.

Is Cystine safe?

Cystine is an amino acid naturally found in the body, and it is generally regarded as safe at the levels used in cosmetics. It is typically present at low concentrations as a supporting ingredient. As with any ingredient, patch testing is reasonable if you have sensitive skin.

What does Cystine do in skincare?

In skincare, Cystine acts mainly as a conditioning ingredient that supports the formula rather than as an active treatment. It is an amino acid and a natural building block of keratin, the protein in hair and the outer skin. It is usually used at low levels alongside other conditioning agents.

Is Cystine vegan?

Cystine used in cosmetics can be produced by fermentation or synthesis, but it can also be derived from animal sources, so its vegan status depends on the supplier. If vegan sourcing matters to you, look for a brand that confirms the origin of its ingredients. The finished product's vegan claim is the most reliable guide.

Sunscreens with Cystine

We rate 8 sunscreens that contain it:

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