Cysteine

Cysteine is a semi-essential amino acid found naturally in the body and in protein-rich foods. In skincare, it's typically derived from yeast extracts or synthesised in laboratories. The ingredient functions primarily as an antioxidant, helping to neutralise free radicals that can damage skin cells.Cysteine is notable for being a building block of glutathione, one of the body's most important antioxidant molecules. When applied topically or consumed orally, cysteine may support the skin's capacity to defend itself against oxidative stress, though research on direct topical application remai…

Cysteine works by supporting the body's glutathione synthesis. Glutathione is a tripeptide antioxidant that neutralises reactive oxygen species (free radicals) before they can damage skin cells and collagen. This protective mechanism helps reduce oxidative stress, which is implicated in photodamage and premature ageing.When consumed orally, cysteine peptides may also support systemic antioxidant defences that protect skin from within. The evidence for topical application is less established, though the ingredient may contribute to formulation stability and skin conditioning.

If using cysteine as part of an oral supplement or functional food, consistency matters more than occasional use; the research suggests regular intake over weeks builds protective benefit. In topical formulations, cysteine is typically used at modest concentrations and works best as part of a broader antioxidant strategy that may include vitamin C, niacinamide, or other protective ingredients. Store products in cool conditions to preserve antioxidant integrity.

Cysteine is generally well-tolerated both orally and topically. Very high oral doses may cause nausea or gastrointestinal discomfort, but cosmetic concentrations are safe for typical use. Those with cystinuria (a rare metabolic disorder) should avoid high-dose cysteine supplementation.