Best For Skin Types
All
Addresses
Usage Frequency
Daily
What Is Cystine?
Cystine is a non-essential amino acid formed when two cysteine molecules bond together. It occurs naturally in the body and is found in protein-rich foods. In skincare and cosmetic formulations, cystine functions primarily as a conditioning agent and antistatic, helping to improve texture and feel.
The ingredient has gained interest in skincare research partly because the body converts cystine into glutathione, a potent antioxidant involved in cellular defence and pigmentation processes. However, topical application differs significantly from oral supplementation in terms of bioavailability and mechanism.
How It Works
Cystine contains a disulfide bond that absorbs ultraviolet radiation, which can help protect other actives (such as retinol) from UV degradation when incorporated into advanced formulations. This protective mechanism is particularly relevant in hydrogel delivery systems designed to minimise irritation and instability of sensitive ingredients.
When consumed as an oral supplement, cystine is metabolised into glutathione, which influences melanin synthesis and may skew production toward lighter pheomelanin rather than darker eumelanin. Topically, evidence for this mechanism is more limited, and the ingredient functions primarily as a conditioning and structural support agent.
Clinical Evidence & References
Oral supplementation studies suggest potential benefits for skin pigmentation and hair health. A 12-week clinical trial in Asian female subjects found that L-cystine combined with reduced glutathione may contribute to skin-lightening effects and reduced dark spots, though the research involved a supplement formulation rather than topical application alone.
Research into cystine-based hydrogel systems shows promise for stabilising and delivering sensitive actives like retinol, with studies demonstrating retained antioxidant activity after UV exposure. However, evidence for topical cystine as a standalone skincare ingredient remains limited, and most clinical benefits have been observed in oral or advanced delivery formulations rather than simple skincare products.
Published Research
How to Use
Cystine appears in relatively few skincare products (approximately 0.2% of formulations surveyed). If seeking cystine for skin health, oral supplementation may offer more substantiated benefits than topical application alone. When present in skincare, it typically supports overall formula stability and texture rather than delivering a primary active benefit. Follow product instructions for frequency and application.
Safety & Precautions
Frequently Asked Questions
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